The COVID-19 Sub-committee of the World Health Organization (WHO) Global Advisory Committee on Vaccine Safety (GACVS) has released its interim statement after reviewing cases of blood clots in people who had received the AstraZeneca COVID-19 vaccine.

It says, “Based on current information, a causal relationship between the vaccine and the occurrence of blood clots with low platelets is considered plausible but is not confirmed. Specialised studies are needed to fully understand the potential relationship between vaccination and possible risk factors.” It said that the cases were rare and, “Active surveillance, including sentinel site / hospital case-based investigations should be considered, to further characterise these rare events.”

“In extensive vaccination campaigns, it is normal for countries to identify potential adverse events following immunization. This does not necessarily mean that the events are linked to vaccination itself, but they must be investigated to ensure that any safety concerns are addressed quickly,” said the statement.

The European Medicines Agency (EMA) safety committee (PRAC) too released a statement saying that they had “concluded today that unusual blood clots with low blood platelets should be listed as very rare side effects of Vaxzevria (formerly COVID-19 Vaccine AstraZeneca).”

It said, “So far, most of the cases reported have occurred in women under 60 years of age within 2 weeks of vaccination. Based on the currently available evidence, specific risk factors have not been confirmed.”

Reports of blood clots emerged starting the middle of March. At least 30 cases of blood clots were reported from the UK alone. These include 22 cases of Cerebral Venous Sinus Thrombosis (CVST), a condition where a blood clot forms in the brain. Cases of blood clots after receiving the vaccine were also reported from Spain, and Germany that had suspended administration of the vaccine following the complaints in March. Concerns were amplified after one person developed blood clots and died in Denmark. Subsequently several countries had decided to halt administering the AstraZeneca vaccine. These include, Denmark, Iceland, Norway, Austria, Bulgaria and many others, but they are now expected to resume using the vaccine to inoculate their citizens.

Both WHO and EMA had made initial reviews of blood clot cases in March itself and concluded that the vaccine’s benefits outweighed risks.

*Feature image courtesy AstraZeneca COVID-19 Visual Resources.