A World Health Organization vaccine advisory group updated guidance on use of the AstraZeneca Covid-19 vaccine Thursday to include the risk of rare but severe blood clots that have been reported in people who received the vaccine.
WHO said it still believes that the benefits of the vaccine outweigh the risks.
The Strategic Advisory Group of Experts on Immunization noted in its guidance that the rare blood-clotting event known as thrombosis with thrombocytopenia syndrome (TTS) has been reported around four to 20 days following vaccination with the vaccine.
The group noted that there has been some geographic variation in reports of the blood clots.
“An estimation of the risk outside Europe needs further data collection and analysis,” the guidance states.
More details: It’s unclear whether pregnancy is linked to a higher risk of TTS, and recommendations may be updated while more data is being collected, the advisory group notes. WHO recommends the use of the vaccine in pregnant women only if the benefits to each woman outweigh the potential risks.
The guidance also included more robust data on the AstraZeneca vaccine in older adults. The advisory group cited a phase 3 trial of the vaccine in the US, which showed an efficacy of 85% in people ages 65 and older.