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expert reaction to CDC and FDA statement recommending a pause in the use of J&J COVID-19 vaccine in the US, and J&J deciding to proactively delay the rollout of the vaccine in Europe

The Centres for Disease Control and Prevention (CDC) and US Food & Drug Administration (FDA) have released a joint statement recommending a pause in the use of the Johnson & Johnson COVID-19 vaccine as it investigates 6 cases of cerebral venous sinus thrombosis (CVST) in combination with low levels of blood platelets (thrombocytopenia) after having received the vaccine. Meanwhile Johnson & Johnson have released a statement saying they have decided to proactively delay the rollout of their vaccine in Europe.


Prof Saad Shakir, Director of the Drug Safety Research Unit (DSRU), said:

“The FDA recommends pausing vaccination with the Johnson and Johnson vaccine in the US.  J&J (Janssen) halts the introduction of their vaccine in the EU.

“The reason is six cases of very rare events of thrombosis, one was with a fatal outcome.  J&J (Janssen) halts the use of this vaccine in the EU.

“Very rare events of thrombosis with thrombocytopenia are consistent with a causal association with the AstraZeneca vaccine, as we heard last week.

“Based on limited information there appears to be clinical similarities between the thrombosis with thrombocytopenia events reported last week with the AZ vaccine, and these six cases after the J&J vaccine.  Taken with the fact these vaccines use the same platform (adenovirus as a vehicle), it seems the mechanism that causes these events may be an issue with DNA adenovirus vector vaccines – the biology of which is yet to be fully understood.

“Pharmacovigilance signals and issues tend to progress over time both biologically and epidemiologically.  We will know more about the biological and epidemiological aspects of these events for the adenovirus vector COVID-19 vaccines.”


Prof Eleanor Riley, Professor of Immunology and Infectious Disease, University of Edinburgh, said:

“Whilst a causal link between certain COVID-19 vaccinations, platelet abnormalities and blood clots has not, so far, been confirmed, the index of suspicion is rising that these rare cases may be triggered by the adenovirus component of the AstraZeneca and J&J vaccines.  Whilst more data need to be collected, and the implications carefully considered, it remains the case that for the vast majority of adults in Europe and the USA the risks associated with contracting COVID-19 far, far outweigh any risk of being vaccinated.  Moreover, increasing awareness of the possibility of such side effects means that they should be diagnosed more quickly and treated more successfully.”


Commenting on the US situation:

Prof Anthony Harnden, Deputy Chair Joint Committee on Vaccination and Immunisation, said:

“Although the UK has ordered 30 million doses of the Jansen vaccine it has not yet been approved by our regulator the MHRA.  The Jansen vaccine uses the same technology platform as the Oxford Astra Zeneca vaccine, albeit a different adenovirus vector.  So although the most recent data about this rare adverse event in the US still has many uncertainties it clearly requires both the MHRA and JCVI to scrutinise any new data related to both vaccines as it emerges.  The observation of cases of thrombosis and thrombocytopenia in those receiving the Jansen vaccine in the US will need to be carefully reviewed – depending on outcomes of any review there may be implications for the recommendation of the Janssen vaccine in the younger age groups in the UK where the risk from severe Covid is much less than in older age groups and in those with underlying illnesses.”


Commenting on the US situation:

Prof Ian Douglas, Professor of Pharmacoepidemiology, London School of Hygiene & Tropical Medicine, said:

“From the limited information available right now, these 6 cases with the J&J vaccine appear to be similar to those seen with the AZ vaccine.  Given the heightened awareness of this issue with COVID vaccines, it’s not surprising that we see more cases being reported as this snowball effect is a well known feature of safety reporting with any medicine.  Whilst it’s too early to conclude whether they are causally related to the vaccine, this type of stimulated reporting is likely to help regulators better determine what’s related to the vaccine and what isn’t.  If a causal link is established, it’s also possible the reports will help us establish possible risk factors for experiencing this outcome, and ultimately help find ways to minimise any risk.

“As we’ve seen, each country makes its own decision about COVID vaccines based on their known risks and benefits, but also other factors such as the availability of other vaccines, circulating virus levels, local vaccine confidence and political pressures.

“It’s vital to stress all indications are that this is incredibly rare, in this instance around a 1 in a million chance based on what we know to date about the J&J vaccine.  To put this into perspective, it’s similar to the chance of being struck by lightning in any given year in the UK.  On the other hand, the risks from COVID-19 are substantial.  If all 6.8 million people who’ve received the J&J vaccine in the US were infected with the virus, several thousand would likely die and many more, including younger adults, would experience serious and long-lasting after effects.”


Commenting on the US situation:

Prof Adam Finn, Professor of Paediatrics, University of Bristol, said:

“The announcement of the recommended suspension of the one dose Janssen COVID vaccine by the authorities in the USA following 6 cases of cerebral venous sinus thrombosis with low platelets among nearly 7 million people given the vaccine echoes recent events in Europe around the Oxford-AstraZeneca vaccine.  These two vaccines are similar in the way they work, using two different adenovirus vectors to carry the coronavirus spike protein gene into the recipient’s arm.  The numbers of cases are, once again, very small but the combination of severe thrombosis with thrombocytopenia is characteristic of the cases that have been reported previously.  Although it’s too soon to draw any firm conclusions, this development does raise the possibility that at least some adenovirus vectors either of themselves or in combination with the SARS CoV2 S protein gene can cause this idiosyncratic reaction in a very small proportion of individuals.  This may help give us a clue towards understanding the mechanism or a way to prevent this problem from occurring.  Given the importance of these vaccines for the timely control of the pandemic, investigation of this phenomenon is now an extremely urgent international priority.”


Commenting on the US situation:

Dr Peter English, Retired Consultant in Communicable Disease Control, Former Editor of Vaccines in Practice Magazine, Immediate past Chair of the BMA Public Health Medicine Committee, said:

“This would appear to be a highly precautionary move by the US’ agencies.

“According to reports to date, there appear to have been six cases of central venous sinus thrombosis (CVST), in over 6.8 million doses of vaccine given.

“The alert related to the AstraZeneca vaccine, where a similar association is considered possible, will have raised awareness of a possible association with other vaccines.  Nevertheless, the fact that such a small possible risk has been identified is very reassuring – it shows that pharmacovigilance systems are working.

“The regulators will be trying to estimate how many such cases would have been expected by chance, and thus what the risk (if any) of vaccination would be.

“Even if all of the cases were caused by the vaccine, the risk of less than one in a million would have to be set against the benefits of protection from Covid-19 disease; a disease which, in itself, causes clotting in many cases.

“The call for a pause may dent confidence in vaccination.  We must hope that, if it does, this will be temporary; and that the rapid action and openness will inspire confidence that vaccine safety is taken extremely seriously.”



Joint CDC and FDA statement:

FDA Twitter feed:

FDA and CDC press conference:

Johnson & Johnson statement:



All our previous output on this subject can be seen at this weblink:



Declared interests

Prof Saad Shakir: “Saad Shakir is an employee of the Drug Safety Research Unit (DSRU), an independent charity (No. 327206), which works in association with the University of Portsmouth.  It receives unconditional donations from pharmaceutical companies.  The DSRU is conducting a safety study of the AstraZeneca vaccine, proactively questioning 10,000 vaccinees about possible side effects. The study is in its early stages and the DSRU will independently publish any findings.  Prof Shakir is a member of the Data Safety Monitoring Boards for Diurnal and Biogen.”

Prof Eleanor Riley: “No COIs to declare.”

Prof Anthony Harnden: “No conflicts.”

Prof Ian Douglas: “I’ve got grants from and shares in GSK, and I sit on the MHRA’s Pharmacovigilance Expert Advisory Group.”

Prof Adam Finn: “AF is an investigator in trials and studies of several COVID19 vaccines including Oxford-AZ, Pfizer, Janssen and Valneva and advises the UK government and the WHO on COVID19 and other vaccines.  He receives no personal income for this work and is remunerated solely through his employment by the University of Bristol.”

Dr Peter English: “No conflict of interest.”


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