A person’s risk of blood clots doesn’t increase after the second Oxford/AstraZeneca coronavirus vaccine shot, according to a new study from AstraZeneca.
The company is trying to boost confidence in its jab, which has taken a beating after reports of rare but serious blood clotting events after vaccination. The study, published this week in the Lancet, could boost people’s confidence in receiving their second dose.
However, the study also confirmed previous reports from regulators that the majority of blood clotting incidents occurred two weeks after the first dose of the viral vector vaccine.
For every million people who received a first shot, there were 8.1 reports of thrombosis with thrombocytopenia syndrome (TTS) — blood clots with low blood platelets. The study looked at a total of 49.23 million people who received the vaccine in the EU, the European Economic Area and the U.K. by the end of April.
After the second dose, there were 2.3 cases out of every million people that reported blood clotting issues. That sample covers 5.62 million who received their second shot within the same time frame.
The company said there were “no specific risk factors or [a] definitive cause” for blood clotting issues associated with its vaccine, developed in partnership with the University of Oxford, and noted it’s continuing to investigate possible causes.
Countries have raised concerns over the vaccine, especially in the EU, where many are only using the vaccine in older populations or donating doses abroad. AstraZeneca claimed this trend could have affected reports of adverse events, writing in the study said that “heightened media attention might have led to event misclassification.”
The vaccine “plays a critical role in combating the pandemic,” Mene Pangalos, AstraZeneca’s executive vice president for biopharmaceuticals R&D, wrote in a statement.
“Unless TTS was identified after the first dose, these results support the administration of the two-dose schedule of [the vaccine] as indicated, to help provide protection against COVID-19 including against rising variants of concern,” Pangalos said.
