Information for Health Professionals
Blood clotting following COVID-19 vaccination
1. What is the condition that has
been reported following COVID-19
vaccination?
Since March 2021 there have been reports from
the UK and internationally of an extremely rare
condition characterised by thromboembolic
events (blood clots) accompanied by
thrombocytopenia (low platelets) following the
rst dose of the AstraZeneca (AZ) COVID-19
vaccination. This includes cerebral venous sinus
thromboses (CVST) where blood clots develop
in the cerebral veins occurring together with low
platelet counts. These cases are particularly
unusual because despite low platelets, there is
progressive thrombosis (formation of blood clots
which block blood vessels).
The cases of venous thromboses that have been
reported include CVST and portal vein thrombosis,
as well as the more usual presentations of deep
vein thrombosis and pulmonary embolism.
Whilst the cases reported to date have primarily
been venous clots, arterial clots have also been
reported. Up to 28 April, 242 suspected cases
have been reported across the UK through the
MHRA Yellow Card scheme following the rst dose
to date, and only a small number of cases have
occurred after the second dose of AZ vaccine.
For the latest information please see the weekly
summary from the MHRA.
Typical laboratory features include a low platelet
count, very raised D Dimer levels – above the
level expected for venous thromboembolism (VTE)
and inappropriately low brinogen. Antibodies
to platelet factor 4 (PF4) have been identied
and so this has similarities to heparin-induced
thrombocytopenia (HIT), but it is occurring without
the patient receiving any heparin treatment.
Further information on the investigation and
treatment of suspected cases has been published
by the Expert Haematology Panel of the British
Society of Haematology and is available here.
2. What are the risk factors for
developing this condition?
This condition is known to occur naturally although
the underlying risk factors have not yet been fully
established. A detailed review of suspected cases
of this condition following COVID vaccination is
ongoing by the MHRA, supported by PHE and
other professional groups. This will help us to
understand the risk factors for developing this
condition. The data reported in the MHRA weekly
report up to the 28 April 2021 estimates an overall
incidence of around 10.5 per million rst doses
of the AZ vaccine administered in the UK. These
data are regularly updated based on the reports
received through the Yellow Card reporting
scheme. For the latest information please see the
weekly summary from the MHRA. Although cases
have been reported in all ages and genders, there
appears to be a trend for increasing incidence with
decreasing age amongst adults, with the highest
incidence reported in the younger adult age groups.
3. Is this condition only associated
with the AZ vaccine?
All suspected cases following vaccination with any
of the COVID-19 vaccines being used in the UK are
undergoing a detailed review by the MHRA.
Up to 28 April 2021, the MHRA received 242
reports of thrombosis events with low platelets of
which 93 were cerebral venous sinus thrombosis
(CVST), out of a total of 22.6 million rst doses of
COVID-19 AZ vaccine given by that date in the UK.
For the latest information please see the weekly
summary from the MHRA.
As with all COVID-19 programme resources, this publication is subject to extensive and
regular revisions and we recommend linking to the latest version to ensure that you are
giving the most up-to-date clinical advice and guidance.
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Blood Clotting following COVID-19 Vaccination
There has also been a small number of reports of a
similar syndrome following receipt of the Johnson
& Johnson/Janssen COVID-19 vaccine (also
an adenovirus vector vaccine, although using a
different vector) in the USA. Following a detailed
investigation and temporary pause in the use of the
vaccine in the USA, the CDC and FDA announced
the resumption of the use of the vaccine for all
age groups on 23 April 2021. This vaccine is not
currently approved for use in the UK. There is
currently no evidence to suggest these rare events
occur following administration of either the Pzer/
BioNTech or Moderna vaccines which are available
in the UK.
Although these extremely rare events have been
associated with the AZ vaccine and Johnson &
Johnson/Janssen vaccines, further investigations
are underway to understand the biological
mechanisms and whether the association is
related to the vaccine platform (the way in which
the vaccine delivers antigen) or some other
immunological mechanism.
4. How many people have developed
the condition?
This condition is known to occur naturally and is
thought to be extremely rare. The background
rate of cerebral venous sinus thromboses (CVSTs)
is estimated to be around 5 to 16 per million
annually, although there is currently limited data
on the background rate of CVSTs occurring with
thrombocytopenia.
Based on reports to 28 April 2021, the overall
incidence following the AZ vaccine is around 10.5
per million rst doses administered. For the latest
information please see the weekly summary from
the MHRA.
It is also important to note that thromboses (blood
clots) have been reported with natural COVID-19
infection and more than a fth of hospitalised
patients with COVID-19 have evidence of blood
clots. A recent preprint of a study based on
analysis of US data showed that CVST was
a complication of COVID-19 infection, with a
higher incidence (42.8 per million) compared
to a matched cohort of patients with inuenza
(RR=3.83, 95% CI 1.56–9.41, P<0.001) and
people who had received an mRNA vaccine
((RR=6.67, 95% CI 1.98–22.43, P<0.001).
5. How many of those affected die?
A detailed review of all suspected cases is
ongoing and based on the reports received by the
MHRA as of 28 April, there were 49 fatal cases
from the 242 events reviewed with an estimated
overall case fatality rate of 20%. This compares
with the clear demonstrable benets from the
COVID vaccination programme. For the latest
information please see the weekly summary from
the MHRA. Since 4 January to 28 April 2021 22.6
million rst doses and 5.9 million second doses of
the AZ vaccine have been administered across
the UK. It has been estimated that the vaccine
programme has prevented 10,400 deaths in adults
aged 60 years and older up to the end of March
with a vaccine effectiveness of a single dose
against hospitalisation estimated at 80% for both
the Pzer/BioNTech and the AZ vaccines.
6. What is the UK’s current advice on
the use of the AZ vaccine?
Based on a review of cases reported to the Yellow
Card Scheme and the evidence of effectiveness
of the COVID vaccines used in the UK to prevent
serious complications and deaths from COVID-19
infection, the current MHRA advice remains that
the overall benets of the use of the AZ vaccine
in the UK vaccine programme outweighs the
extremely rare adverse events reported to date.
The Joint Committee on Vaccination and
Immunisation (JCVI) has carefully assessed the
overall risk benet of the use of the AZ vaccine in
the UK population and continues to keep this under
active review. After considering the relative balance
of benets (in terms of deaths, ICU and hospital
admissions averted estimated by Public Health
England) and risks (based on data presented by
the MHRA on reported adverse events through the
Yellow Card Scheme), on 7 April 2021, JCVI advised
that, for adults aged <30 years without underlying
health conditions that put them at higher risk of severe
COVID-19 disease, there should be a preference
for an alternative to the AZ vaccine, if available.
The MHRA has continued to review cases of
these extremely rare adverse events, including
those reported retrospectively, and data on the
frequency of these events by age are now more
precise. The available data continues to suggest a
trend of increasing incidence of this condition with
decreasing age amongst adults, with the highest
incidence reported in the younger adult age
groups. In contrast, the risks of serious disease
associated with COVID-19 increases steeply with
age, with the younger adults at the lowest risk of
serious disease. Amongst healthy adults under 50
years, there continues to be an age-related risk of
severe complications from COVID-19.
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Blood Clotting following COVID-19 Vaccination
For example, the risk of dying in an individual
aged 40-49 years is 3 times higher than someone
aged 30-39 years and 12 times higher than
someone aged 20-29 years.
JCVI have continued to review the available data
on the current epidemiology, benet-risk prole
by age, modelling predictions on future disease
trends and the current forecast on vaccine supply.
Given the risk (albeit extremely rare) of these
adverse events associated with the AZ vaccine,
the current control of COVID-19 in the UK, model
predictions of the potential scale and timing of
a future wave, and promising forecasts for the
availability of vaccines in the UK, JCVI has issued
updated advice on 7 May 2021.
• in addition to those aged under 30, unvaccinated
adults aged 30–39 years who are not in a clinical
priority group at higher risk of severe COVID-19
disease, should be preferentially offered an
alternative to the AZ vaccine, where possible
and only where no substantial delay or barrier in
access to vaccination would arise.
• for those within this age group who are of older
age, male, obese (BMI >30), from certain ethnic
minority backgrounds or experiencing socio-
economic deprivation, the risks of acquiring
and/ or suffering complications of COVID-19 are
higher. Every effort should be made to remove
barriers to accessing vaccination in those
individuals. These individuals can choose to
have the AZ vaccine if they have been provided
with information on the risks and benets of the
vaccine.
• for those aged 18-29 years the precautionary
advice for a vaccine preference is stronger,
reecting a gradient in the benet-risk balance
with age.
This new advice is specic to the current UK
context and is based on all of the following
remaining favourable: the current low incidence
of disease, the availability of alternatives to the AZ
vaccine, and the strength of the whole vaccine
programme in terms of maintaining speed and
uptake. Should there be a deterioration in any of
the above factors, JCVI advises that vaccination
of adults aged 30-39 years with any of the UK
authorised vaccines is always better than no
vaccination, except where there are specic
contraindications.
Healthy adults aged 40-50 years who are offered
vaccine are recommended to receive any of the
available COVID-19 vaccines. Those who have
received their rst dose of AZ vaccine without
suffering this rare side effect, should continue
to be offered the second dose to complete
the course (see the Green Book for further
information).
The AZ vaccine should also continue to be offered
to those in the priority groups (which includes
older adults, those with underlying conditions,
health and social care workers over 40 years
old) who have not yet been offered the vaccine.
Those who have received their rst dose of AZ
vaccine without suffering this rare side effect,
should continue to be offered the second dose
to complete the course. This includes individuals
aged 18 to 39 years who have received their rst
dose of AZ vaccine in the initial priority groups,
which includes those who are health and social
care workers, unpaid carers and family members
of those who are immunosuppressed.
Due to its storage and transport requirements,
the AZ vaccine is much more easily delivered
in some settings, and in these settings may be
the only vaccine it is practical to offer. In such
circumstances JCVI advises that the benets of
receiving the AZ vaccine outweigh the risks, and
individuals in this event should be offered the AZ
vaccine.
JCVI considers that there continues to be no
safety concerns for this extremely rare adverse
event following receipt of a second dose of AZ
vaccine. All those who have received a rst dose
of the AZ vaccine should continue to be offered a
second dose of AZ vaccine, irrespective of age.
The second dose will be important for longer
lasting protection against COVID-19.
7. Can COVID-19 infection cause the
same problem?
Thrombotic events are known to occur in
individuals with natural COVID-19 infection
and more than a fth of hospitalised patients
with COVID-19 have evidence of blood clots.
A preprint of a study based on analysis of US
data showed that CVST was a complication of
COVID-19 infection, with a higher incidence (42.8
per million) compared to a matched cohort of
patients with inuenza (RR=3.83, 95% CI 1.56–
9.41, P<0.001) and people who had received an
mRNA vaccine ((RR=6.67, 95% CI 1.98–22.43,
P<0.001). However, this particular combination
of thrombotic events and thrombocytopenia is
extremely rare and not known to be a common
feature of COVID-19 infection. Based on cases
reported to MHRA as of 28 April 2021, the overall
incidence following the AZ vaccine is estimated at
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Information for Health Professionals
Blood Clotting following COVID-19 Vaccination
10.5 per million rst doses administered. For the
latest information please see the weekly summary
from the MHRA.
8. Has this condition been reported
after both the 1st and 2nd dose of
COVID-19 vaccine?
As of 28 April 2021, of the 242 suspected cases
reported to the MHRA following the AZ vaccine,
only a very small number of cases have been
reported after the second dose. The JCVI
concluded that there continues to be no safety
concerns following the second dose of vaccine.
Whilst currently there is no evidence to suggest
whether these rare events are dose specic it is
important to note that most vaccines in the UK
COVID-19 programme have been administered as
rst doses.
The JCVI advises that those who have received
their rst dose of AZ vaccine should continue to
be offered the second dose unless they have
developed this specic syndrome of thrombosis
and thrombocytopenia following the rst dose or
have had an anaphylactic reaction. The Green
Book has further information on contraindications
to COVID-19 vaccines.
9. Is it affecting both men and women?
Suspected cases have been reported in patients
of all ages in men and women. Whilst reports from
some countries have suggested a substantially
higher number of cases amongst females, based
on the events reported to the MHRA in the UK,
such a distinctive gender difference has not
been observed. Although, the reported incidence
rate is higher in females compared to males,
this is not seen across all age groups and the
difference remains small.
It is worth noting that more females have been
vaccinated which may partly explain the slight
excess of cases reported amongst females.
10. Is it affecting any particular
community?
Suspected cases have been reported in patients
of all ages and genders and currently, no specic
predisposing factors have been identied. There
appears to be a trend of increasing incidence
of this condition with decreasing age amongst
adults, with the highest incidence reported in the
younger adult age groups.
11. What are the signs and symptoms?
While the detailed case review is ongoing, it is
important to ensure all health professionals are
alert to relevant symptoms which require further
clinical review and investigation. Advise patients
to seek urgent medical advice if they experience
any of the following symptoms more than 4 days
and within 28 days of coronavirus vaccination:
• new onset of severe headache, which is
getting worse and does not respond to simple
painkillers
• an unusual headache which seems worse
when lying down or bending over, or may be
accompanied by blurred vision, nausea and
vomiting, difculty with speech, weakness,
drowsiness or seizures
• new unexplained pinprick bruising or bleeding
• shortness of breath, chest pain, leg swelling or
persistent abdominal pain
If you have clinical concern, patients should be
urgently referred to hospital and to appropriate
specialist services for further assessment,
particularly if the symptoms are unexplained and
present in combination with thrombocytopaenia.
Further guidance for secondary care are available
here with specic guidance produced for
Emergency Departments and Acute Medical Units
and primary care.
Mild u-like symptoms, including headache, chills
and fever remain one of the most common side
effects of any COVID-19 vaccine. These generally
appear within a few hours and resolve within a day
or two.
12. What should I do if I suspect a case?
If a patient presents with symptoms suggestive
of a blood clot in this time period please take the
following actions:
Immediately refer patients to their local Emergency
Department to have a Full Blood Count and further
investigations carried out.
Report this case via the MHRA Yellow Card System
(https://coronavirus-yellowcard.mhra.gov.uk).
At Emergency Departments, the standard Royal
College of Emergency Medicine pathway should
be followed and supportive guidance is available
through local haematology teams for cases
with conrmed thrombocytopenia <150 x 10
9
/l.
Further guidance for secondary care is available
here, with specic guidance for Emergency
Departments and Acute Medical Units.
In the UK, the MHRA are reviewing all reported
cases to the COVID-19 Yellow Card scheme.
In order to support the case reporting, clinical
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Information for Health Professionals
Blood Clotting following COVID-19 Vaccination
review and investigation, PHE has established
an electronic clinical reporting scheme collecting
patient identiable information on all suspected
cases.
All health professionals are also
encouraged to report any suspected case at
https://snapsurvey.phe.org.uk/
snapwebhost/s.asp?k=161706705032 with details
of the clinical presentation, dates of vaccination,
vaccine product received and any underlying
conditions.
13. How should I report suspected cases?
It is very important that all suspected cases are
reported to both the MHRA on the COVID-19
Yellow Card scheme and to PHE’s clinical
reporting scheme at https://snapsurvey.phe.org.
uk/snapwebhost/s.asp?k=161706705032.
The PHE clinical reporting scheme collects patient
identiable information with details of the clinical
presentation, dates of vaccination, vaccine
product received and any underlying conditions.
In order to minimise burden on reporters, for
cases reported on the PHE clinical reporting
scheme rst, the last page of the survey allows all
the inputted answers to be copied, and relevant
information can then be directly pasted into the
COVID-19 Yellow Card form.
14. Are there any contraindications or
cautions to receiving the AZ vaccine?
The contraindications to vaccination with the AZ
vaccine include individuals who have a history
of heparin induced thrombocytopaenia and
thrombosis (HITT or HIT type 2). These individuals
may be offered vaccination with an alternative
COVID-19 vaccine. A history of thromboses on
its own is not a contraindication to the vaccine.
Individuals who experience thrombosis with
thrombocytopenia following the rst dose of
the AZ vaccine should be properly assessed
and if they are considered to have the reported
condition, vaccination should be delayed until
their clotting has completely stabilised and they
should be considered for a second dose of an
alternative COVID-19 vaccine. The Green Book
has further information on contraindications and
cautions to receiving the AZ vaccine.
Individuals aged 40 years or older with past
clotting episodes and those diagnosed with
thrombophilia, whether or not they are on long
term anti-coagulation, remain at risk of COVID-19
disease and should be vaccinated with any of the
available vaccines (provided they are not otherwise
contraindicated). The same consideration applies
to those who experience common clotting
episodes, without concomitant thrombocytopaenia,
after the rst dose of AZ vaccine.
The Expert Haematology Panel advise that
there is no evidence that individuals with a
prior history of thrombosis or known risk factors
for thrombosis are more at risk of developing
the immune complication reported after the
AZ vaccine. Furthermore, for the majority of
individuals, the risk of recurrent thrombosis due
to COVID-19 infection is far greater than the risk
of this syndrome.
15. Should we still give people their
second dose?
Yes, because of the high risk of complications and
death from COVID, the MHRA, the World Health
Organization and the European Medicines
Agency have concluded that the balance is very
much in favour of vaccination. There are currently
no safety concerns following receipt of the second
dose of vaccine. There are no known risk factors
for this extremely rare condition, which appears
to be an idiosyncratic reaction on rst exposure
to the AZ vaccine. The JCVI advises that those
who have received their rst dose of AZ vaccine
without suffering this rare side-effect they should
continue to be offered the second dose to complete
the course.
16. Can my patient receive the AZ
vaccine if they have previously had a
blood clot?
Importantly, a history of thromboses on its own
is not a contraindication to the vaccine and
individuals should be reassured that they can still
receive the AZ vaccine when offered.
The contraindications to vaccination with the
AZ vaccine include individuals who have a
history of heparin induced thrombocytopaenia
and thrombosis (HITT or HIT type 2). These
individuals may be offered vaccination with an
alternative COVID-19 vaccine. Individuals who
experience thrombosis with thrombocytopenia
following the rst dose of the AZ vaccine
should be properly assessed and if they are
considered to have the reported condition,
vaccination should be delayed until their clotting
has completely stabilised and they should be
considered for a second dose of an alternative
COVID-19 vaccine. The Green Book has further
information on contraindications and cautions to
receiving the AZ vaccine.
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Information for Health Professionals
Blood Clotting following COVID-19 Vaccination
Individuals over 40 years or older with past clotting
episodes and those diagnosed with thrombophilia,
whether or not they are on long term anti-
coagulation, remain at risk of COVID-19 disease
and should be vaccinated with any of the available
vaccines (provided they are not otherwise
contraindicated). The same consideration applies
to those who experience common clotting
episodes, without concomitant thrombocytopaenia,
after the rst dose of AZ vaccine.
The Expert Haematology Panel advise that
there is no evidence that individuals with a
prior history of thrombosis or known risk factors
for thrombosis are more at risk of developing
the immune complication reported after the
AZ vaccine. Furthermore, for the majority of
individuals, the risk of recurrent thrombosis due
to COVID-19 infection is far greater than the risk
of this syndrome.
If a patient has a history of, for example, a deep
venous thrombosis (DVT) or pulmonary embolus
(PE) without concurrent thrombocytopenia, then
they can receive the AZ vaccine. Likewise, if they
have had an arterial thrombosis e.g. myocardial
infarction without thrombocytopenia then they
can receive the AZ vaccine.
Many patients who have had a history of blood
clots may be concerned as to whether they also
had low platelets at the same time. This is likely to
have been communicated at the time of diagnosis
of the blood clot and be recorded in the patient’s
medical records. In the absence of this being
recorded in the patient’s medical records, such
individuals can be offered the AZ vaccine.
A revision to the COVID-19 Green book chapter
is available with updated information on cautions
and contraindications for the AZ vaccine.
17. Can my patient receive the AZ
vaccine if they have been or are
currently thrombocytopenic?
Thrombocytopaenia on its own is not a
contraindication to receiving the AZ vaccine.
The contraindications to vaccination with the AZ
vaccine include individuals who have a history
of heparin induced thrombocytopaenia and
thrombosis (HITT or HIT type 2). These individuals
may be offered vaccination with an alternative
COVID-19 vaccine. Individuals who experience
thrombosis with thrombocytopenia following the
rst dose of the AZ vaccine should be properly
assessed and if they are considered to have the
reported condition, vaccination should be delayed
until their clotting has completely stabilised and
they should be considered for a second dose of
an alternative COVID-19 vaccine. The Green Book
has further information on contraindications and
cautions to receiving the AZ vaccine. Individuals
with bleeding disorders can still be vaccinated and
further information is available in the Green Book.
18. What if someone has had a cerebral
or major blood clot with low levels of
platelets following the rst dose of AZ
vaccine?
Individuals who experience thrombosis with
thrombocytopenia following the rst dose of the AZ
vaccine should be properly assessed and if they
are considered to have the reported condition,
vaccination should be delayed until their clotting
has completely stabilised and they should be
considered for a second dose of an alternative
COVID-19 vaccine (see the Green Book).
19. Can my patient still have a second
dose of AZ vaccine if they had a blood
clot after the rst dose?
Importantly, a history of thromboses on its own
(without thrombocytopaenia) following the rst
dose of AZ vaccine is not a contraindication
to receiving their second dose and individuals
should be reassured that they can still receive the
AZ vaccine when offered.
The contraindications to vaccination with the AZ
vaccine include individuals who have a history
of heparin induced thrombocytopaenia and
thrombosis (HITT or HIT type 2). These individuals
may be offered vaccination with an alternative
COVID-19 vaccine.
A history of thromboses on its own is not a
contraindication to the vaccine. Individuals who
experience thrombosis with thrombocytopenia
following the rst dose of the AZ vaccine should
be properly assessed and if they are considered
to have the reported condition, vaccination should
be delayed until their clotting has completely
stabilised and they should be considered for a
second dose of an alternative COVID-19 vaccine.
The Green book has further information on
contraindications and cautions to receiving the AZ
vaccine.
The Expert Haematology Panel advise that there
is no evidence that individuals with a prior history
of thrombosis or known risk factors for thrombosis
are more at risk of developing the immune
complication reported after the AZ vaccine.
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Blood Clotting following COVID-19 Vaccination
Furthermore, for the majority of individuals, the risk
of recurrent thrombosis due to COVID-19 infection
is far greater than the risk of this syndrome.
Individuals who experience a clotting episode
WITH concomitant thrombocytopenia following
the rst dose of AZ vaccine should be properly
assessed; if they are considered to have the
reported condition, further vaccination should
be deferred until their clotting has completely
stabilised and should then be boosted with an
alternative product.
In the UK about 1 in 1,000 people are affected
by venous thrombosis each year. This compares
with reports up to 28 April to the MHRA of 242
thrombosis events with low platelets out of a total
of 22.6 million rst doses of AZ vaccine given by
that date.
Therefore, by chance a lot of people will have
blood clots after vaccination which are not due to
this syndrome.
20. What if somebody under 40 years
has had AZ for their rst dose – should
they have the second?
The AZ vaccine should continue to be offered
to those in priority groups who have not yet
been offered the vaccine. This includes older
adults, those with underlying conditions, health
and social care workers 40 years or older.
There are currently no known risk factors for this
extremely rare condition, which appears to be an
idiosyncratic reaction on rst exposure to the AZ
vaccine.
Those who have received their rst dose of AZ
vaccine and have not suffered this rare side-
effect should continue to be offered the second
dose to complete the course. Individuals aged
18 to 39 years who have received their rst
dose of AZ vaccine, without suffering this rare
side effect, should complete their course with
the same vaccine. This will include those who
are eligible as part of the initial priority groups,
such as health and social care workers, unpaid
carers and family members of those who are
immunosuppressed.
There is currently no evidence on the
interchangeability of the COVID-19 vaccines
although studies are underway. Therefore,
every effort should be made to determine which
vaccine the individual received and to complete
with the same vaccine.
Please see the Green Book for further advice on
vaccination.
21. Will taking aspirin before vaccination
with the AZ vaccine reduce the clotting
risk for my patients’?
It is NOT recommended to take aspirin before
vaccination with AZ, unless this is already part of
your patient’s regular medications.
Investigations are underway to understand the
biological mechanisms behind this extremely
rare condition of thromboembolic events with
thrombocytopenia and whether the association
is related to the vaccine platform (the way in
which the vaccine delivers antigen) or some other
immunological mechanism. Whilst aspirin may be
used to reduce clotting risk in other conditions, it
is not currently thought to have the same effect in
this condition and may in fact worsen the outcome
by increasing the risk of bleeding. Therefore no
one should self-medicate with aspirin to cover the
period around and after the vaccination.
22. How can I communicate the
potential benets and risks of the AZ
vaccine to my patients?
Resources, such as patient information leaets,
have been produced which explain the benets
and risks of the AZ vaccination by different age
bands. Older age groups, such as those aged
50 or older or with underlying medical problems,
have a higher risk of hospitalisation, intensive care
admission or death from COVID-19 infection than
younger age groups:
• for those aged 50 and older or with underlying
medical problems, the risk of this very rare side
effect is around 1 in every 100,000 rst doses
and the benet of one dose of the vaccine is
an 80% reduction in deaths, hospitalisation and
intensive care
• for people aged 40–49, the risk of this very
rare side effect is around 1 in every 100,000
rst doses and the benet of one dose of the
vaccine is 60 – 70% reduction in catching and
passing on the infection
• for people aged 18–39, the risk of this very
rare side effect is around 1 in every 50,000
rst doses and the benet of one dose of the
vaccine is 60%–70% reduction in catching and
passing on the infection
Someone who is vaccinated will continue to
accrue benets from the vaccination in the longer
term by being protected against COVID-19, whilst
the risk of vaccination occurs only in the few
weeks after vaccination.
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Blood Clotting following COVID-19 Vaccination
23. What if my patient refuses the AZ
vaccine?
To make an informed decision it is important that all
individuals are provided with the relevant information,
including the benets and risks, and that they have
the opportunity to discuss this with their healthcare
provider if they wish. If the patient is under 40 years,
an alternative vaccine will become available, but
they may need to go to a different vaccination site.
Resources, including patient leaets, are available to
support decision making.
24. What if my patient under 40 years old
wants to have the AZ vaccine?
Patients under 40 who decide to go ahead after
they have considered all the risks and benets can
be vaccinated with the AZ vaccine. You should
document that you have had a full conversation
with the patient and that you have provided them
with sufcient information for them to give informed
consent to vaccination. Resources, including patient
leaets, are available to support decision making.
25. Can patients taking the combined
oral contraceptive pill have the AZ
vaccine?
Yes, patients taking the combined oral
contraceptive pill can have the AZ vaccine, if
they do not have any of the contraindications or
cautions to its use (see the Green Book for further
information).
The JCVI has concluded that for adults under 40
years of age who are not in a clinical risk group, it is
preferable to offer an alternative to the AZ vaccine
if available. Healthy adults aged 40-50 years are
recommended to receive any of the available
COVID-19 vaccines. Those who have received their
rst dose of AZ vaccine without suffering this rare
side-effect should continue to be offered the second
dose to complete the course.
Patients who are taking the combined oral
contraceptive pill may be concerned that they have
an increased risk of thrombosis and should not have
the AZ vaccine. The Expert Haematology Panel
advise that there is no evidence that individuals with
a prior history of thrombosis or known risk factors
for thrombosis are more at risk of developing the
immune complication reported after the AZ vaccine.
Furthermore, for the majority of individuals, the risk
of recurrent thrombosis due to COVID-19 infection
is far greater than the risk of this syndrome. The
Faculty of Sexual and Reproductive Healthcare
have published a statement on this topic FSRH
CEU statement: Cerebral venous sinus thrombosis
AstraZeneca COVID-19 vaccination and CHC –
Faculty of Sexual and Reproductive Healthcare
26. What is the current advice for
pregnant women?
There have been no conrmed cases of this
syndrome in pregnant women to date, and
prothrombotic states such as pregnancy and
contraception are not likely to confer a higher risk.
The Expert Haematology Panel advise that there is
no evidence that individuals with a prior history of
thrombosis or known risk factors for thrombosis are
more at risk of developing the immune complication
reported after the AZ vaccine. However, because
of more extensive experience and available safety
data for Pzer and Moderna vaccines from the USA,
these vaccines are preferred in pregnancy. Further
information is available in the Green Book.
27. What investigations do I need to
organise for cases?
If a patient presents with symptoms suggestive
of a blood clot in this time period please take the
following actions:
Immediately refer patients to their local Emergency
Department to have a Full Blood Count and further
investigations carried out.
Report this case via the MHRA Yellow Card System
(https://coronavirus-yellowcard.mhra.gov.uk).
At Emergency Departments, the standard Royal
College of Emergency Medicine pathway should
be followed and supportive guidance is available
through local haematology teams for cases with
conrmed thrombocytopenia <150 x 10
9
/l. Further
guidance for secondary care is available here, with
specic guidance for Emergency Departments and
Acute Medical Units.
In the UK, the MHRA are reviewing all reported
cases to the COVID-19 Yellow Card scheme.
In order to support the case reporting, clinical
review and investigation, PHE has established
an electronic clinical reporting scheme collecting
patient identiable information on all suspected
cases.
All health professionals are also
encouraged to report any suspected case at
https://snapsurvey.phe.org.uk/
snapwebhost/s.asp?k=161706705032 with details
of the clinical presentation, dates of vaccination,
vaccine product received and any underlying
conditions.
Information correct at time of publication. For the latest version of this factsheet,
visit the PHA website www.publichealth.hscni.net/publications
© Crown copyright 2021. This information was originally developed by Public Health
England and is used under the Open Government Licence v3.0
Vaccination, helping to protect those most vulnerable.
07/21
Sources
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Coronavirus Yellow Card reporting site Ofcial MHRA side effect and adverse incident reporting site for
coronavirus treatments and vaccines | Coronavirus (COVID-19)
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JCVI nal statement on phase 2 of the COVID-19 vaccination programme: 13 April 2021: www.gov.uk/
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