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The critical role of background rates of possible adverse events in the assessment of COVID-19 vaccine safety
An article in the March edition of Vaccine explains why it is necessary to know the background rates of possible Adverse Events of Special Interest (AESI) when monitoring the safety of COVID-19 vaccines. The article provides examples to illustrate the use of background rates and discusses tools available from the Brighton Collaboration that facilitate case evaluation and understanding of AESI.
The UK Expert Haematology Panel (EHP) has produced guidance on the syndrome of Thrombosis and Thrombocytopenia occurring after coronavirus vaccination
The Expert Haematology Panel is comprised of UK blood clotting experts, who are meeting daily to collect information on possible cases and are in regular communication with the regulators and other haematology groups studying this potential problem in other European countries. Their guidance includes a link to a living document and the contact details for advice from the Expert Haematology Panel. They state that it is important that correct management is applied to prevent the progression of thrombosis. Of critical note, platelet transfusions should be avoided.
A news item in Nature by Ariana Remmel explains how challenging it is to prove that a medical problem following immunization was caused by the vaccine itself and describes the kinds of studies that are needed to understand the causes of rare adverse events. These include targeted clinical trials and active surveillance systems that collect adverse event data, both background rates and rates after vaccination, from electronic health records.
Protocol template for cohort event monitoring (CEM) for safety signal detection after vaccination with COVID-19 vaccines
The WHO has published the COVID-19 vaccines: safety surveillance manual to guide the processes for collecting, analysing and sharing safety data and information on COVID-19 vaccines within and across countries. To accompany this manual and facilitate the conduct of active safety surveillance studies using harmonized tools and methods, a protocol template for cohort event monitoring (CEM) studies has been developed. Read more about development of the protocol template, the cohort event monitoring (CEM) study design, and how it can identify previously unrecognised and unsuspected adverse reactions to the vaccine. The CEM protocol was commissioned by World Health Organization (WHO), coordinated by Dr. Christine Guillard with the support of Dr. Noha Iessa, in the Pharmacovigilance (PVG) team, within the Regulation and Prequalification department at WHO Headquarters.
COVID-19 Vaccine AstraZeneca: benefits still outweigh the risks despite possible link to rare blood clots with low blood platelets
The European Medicines Agency’s safety committee, the Pharmacovigilance Risk Assessment Committee, concluded its preliminary review of a signal of blood clots in people vaccinated with COVID-19 Vaccine AstraZeneca at its extraordinary meeting of 18 March 2021. The Committee confirmed that:
- the benefits of the vaccine in combating the still widespread threat of COVID-19 (which itself results in clotting problems and may be fatal) continue to outweigh the risk of side effects;
- the vaccine is not associated with an increase in the overall risk of blood clots (thromboembolic events) in those who receive it;
- there is no evidence of a problem related to specific batches of the vaccine or to particular manufacturing sites;
- however, the vaccine may be associated with very rare cases of blood clots associated with thrombocytopenia, i.e. low levels of blood platelets (elements in the blood that help it to clot) with or without bleeding, including rare cases of clots in the vessels draining blood from the brain (CVST).
The Vaccine Safety Technical Subgroup of the US CDC’s Advisory Committee on Immunization Practices (ACIP) met on March 1, 2021 to share vaccine safety experience updates and to discuss three sources of vaccine safety monitoring information: Digital apps, Passive surveillance, and the Vaccine Safety Datalink. A video of the one hour long meeting has been posted on YouTube. The updates will be published in the CDC’s Morbidity and Mortality Weekly Report (MMWR) but there’s a great summary of the three sources of vaccine safety monitoring information on the Skeptical Raptor blog, which regularly comments on the science of vaccines.
Work is under way at the Department of General Practice and Primary Health Care within the University of Auckland to gather baseline data on medical events that have potential to be associated with COVID-19 vaccines. Defining these potential Adverse Events of Special Interest (AESI) and calculating the rate at which they have occurred in New Zealand in the past are prerequisites for monitoring the safety of COVID-19 vaccines. If these adverse events occur after a vaccine is introduced to the population, New Zealand will have a frame of reference with which to compare the rates of these events to assess if there is a safety concern or not. The Brighton Collaboration has already defined 22 AESI and Assoc. Prof. Helen Petousis-Harris and her team are currently gathering data to calculate the background rates of these events, with funding provided by the New Zealand Ministry of Health.
While there may have been a lot of attention on developing COVID vaccines, there has been less interest in investing in the vaccine safety monitoring mechanisms required under these extraordinary conditions. There is an urgency to get these systems in place both nationally and globally. An article in the New York Times explains how the much-touted system the government designed to monitor any dangerous reactions won’t be capable of analyzing safety data for weeks or months, according to numerous federal health officials.
The vaccines from Pfizer and Moderna both use tiny snippets of genetic code called messenger RNA, or mRNA, to prompt the immune system into producing antibodies to the coronavirus, without using bits of the virus itself. For more information, read the USA CDC article entitled ‘Understanding mRNA COVID-19 Vaccines’.
Mario Christodoulou* recently spoke with vaccine safety expert, Dr Robert Chen, Science Director of The Brighton Collaboration — the largest global organisation of scientific experts on vaccine safety — about how vaccine safety is assessed in clinical trials and how regulators and vaccine developers are ensuring the safety of COVID-19 vaccines whilst also moving at great speed.
Dr Chen answers questions such as ‘How can we be sure safety isn’t being compromised?’ and ‘What should we be focused on once COVID-19 vaccines are introduced?’ Dr Chen is also working with CEPI, as part of the Safety Platform for Emergency vACcines (SPEAC) Project, to examine the safety profiles of the COVID-19 vaccines CEPI is funding.
*Mario Christodoulou is Communications and Advocacy Manager at the Coalition for Epidemic Preparedness Innovations (CEPI), a global partnership launched in 2017 to develop vaccines to stop future epidemics.