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A news article in Nature describes a study led by the Carlos III Health Institute in Madrid that explored the benefits of combining different coronavirus vaccines. Preliminary results show that vaccinating people with both the Oxford–AstraZeneca and Pfizer–BioNTech COVID-19 vaccines produces a potent immune response against the virus SARS-CoV-2. The trial of more than 600 people — announced in an online presentation on 18 May — is the first to show the benefits of combining different coronavirus vaccines.
Because of safety concerns, several European countries are already recommending that some or all people who were given a first dose of the Oxford–AstraZeneca vaccine get another vaccine for their second dose. Researchers hope that such mix-and-match COVID-19 vaccination regimens will trigger stronger, more robust immune responses than will two doses of a single vaccine, while simplifying immunization efforts for countries facing fluctuating supplies of the various vaccines.
Arterial events, venous thromboembolism, thrombocytopenia, and bleeding after vaccination with Oxford-AstraZeneca in Denmark and Norway
A recent article in the BMJ describes a population based cohort study that assessed rates of cardiovascular and haemostatic events in the first 28 days after vaccination with the Oxford-AstraZeneca vaccine ChAdOx1-S in Denmark and Norway, and compared them with rates observed in the general populations.
The researchers observed increased rates of venous thromboembolic events, including cerebral venous thrombosis, among recipients of ChAdOx1-S. For the remaining safety outcomes, the researchers observed slightly higher rates of thrombocytopenia/coagulation disorders and bleeding, which could be influenced by increased surveillance of vaccine recipients. The absolute risks of venous thromboembolic events were, however, small, and the findings should be interpreted in the light of the proven beneficial effects of the vaccine, the context of any given country, and the limitations to the generalisability of the study findings.
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.