Recent news of the possible complications of blood clots – or Thrombosis with Thrombocytopenia Syndrome – following the AstraZeneca/Oxford and Johnson & Johnson/Janssen COVID-19 vaccines have raised public concerns and questions about vaccine safety, a topic with which The Task Force is deeply involved.
On April 13, the U.S. Centers for Disease Control and Prevention (CDC) and Federal Drug Administration (FDA) initiated a pause on J&J/Janssen’s vaccine in the U.S. to gather more information and provide recommendations on further use of the vaccine. Similar action was taken by other national health authorities earlier with the AstraZeneca/Oxford vaccine.
“Their decision to pause administration of the two new vaccines until they have gathered more data despite the apparent rarity of Thrombosis with Thrombocytopenia Syndrome is understandable, given the severity of the illness and that the standard treatment actually worsens the illness, along with the fact that alternative COVID-19 vaccines are available in most of these countries,” said Dr. Robert Chen, Scientific Director for the Brighton Collaboration, a Task Force program that oversees a global network of 1,000 vaccine safety experts.
The Brighton Collaboration, through the Safety Platform for Emergency vACcines project funded by the Coalition for Epidemic Preparedness Innovation, helped to harmonize the safety protocols during the development and testing of many COVID-19 vaccines. However, as is always the case with new vaccines, very rare adverse events can only be detected once vaccines are used in large numbers.
Once Thrombosis with Thrombocytopenia Syndrome emerged as a safety concern, the Brighton Collaboration was invited by the European Medicines Agency to rapidly develop a standard case definition. Case definitions are the clinical criteria and diagnostic guides that standardize the diagnosis of an adverse health event if there is a report of a person falling ill post-vaccination. These definitions are used by the World Health Organization, public health agencies, and health professionals to identify cases of a new illness and to avoid misdiagnosis.
The usual case definition takes months to develop, however, Thrombosis with Thrombocytopenia Syndrome’s definition was developed in approximately two weeks. This was possible because Brighton had previously developed case definitions for both Thrombocytopenia and Thrombosis. As next steps, Brighton is organizing a process to collect and share information on the possible cases that meet the case finding definition. This will provide evidence for the investigation into whether or not the illness could be linked to the vaccination, and if so, the mechanism for adapting the approach.
Most countries with strong health systems have a reporting system in place for adverse events following immunization to which any individual can report an incident. In the U.S., this is the CDC’s Vaccine Adverse Event Reporting System. Reporting an incident does not prove that a vaccine is the cause but can trigger investigations if new adverse events are identified.
“Serious adverse health responses to vaccines are very rare, but it’s important that we have these monitoring systems in place around the world,” said Chen.
As of April 12, more than 6.8 million doses of the J&J/Janssen vaccine had been administered in the U.S., with six reported U.S. cases of Thrombosis with Thrombocytopenia Syndrome. These cases have been similar to those identified in Australia and Europe after the AstraZeneca vaccine, which has not been approved for use in the U.S. by the FDA yet, but vaccine experts say that more data needs to be collected from low- and middle-income countries where reporting is not as robust.
Pfizer and Moderna’s COVID-19 vaccines have not had similar reports but safety monitoring continues on these vaccines with regulatory health authorities like the CDC looking closely at all incidents reported.
“People who received the J&J/Janssen or AstraZeneca vaccine might be worried that this vaccine could harm them, but to put it in perspective, a person is twice as likely to become an Olympian than to suffer this rare reaction,” said Karen Ernst, Director of The Task Force’s Voices for Vaccines program, which provides parents with clear, science-based information about vaccines and vaccine-preventable disease.
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