Rates of the very rare clotting disorder following a second dose of AstraZeneca vaccine are comparable to the background rate in an unvaccinated population, the research noted
Oxford-AstraZeneca covid-19 vaccine also known as covishield in India showed a small risk of very rare blood clotting disorder after the first dose and no increased incidence after second dose, indicated a study published in The Lancet on Wednesday.
The analysis was conducted using AstraZeneca’s global safety database, which captures all spontaneously reported adverse events from real-world use of its medicines and vaccines worldwide.
Rates of the very rare clotting disorder, thrombosis with thrombocytopenia syndrome (TTS), following a second dose of AstraZeneca vaccine are comparable to the background rate in an unvaccinated population, the research noted.
Reported cases of TTS globally were included up to the cut-off date of April 30 occurring within 14 days of administration of the first or second dose of Oxford-AstraZeneca vaccine.
The data demonstrated the estimated rate of TTS following a second dose of Oxford-AstraZeneca vaccine was 2.3 per million vaccinees, comparable to the background rate observed in an unvaccinated population. It was 8.1 per million vaccinees after the first dose. The rate after the second dose is comparable to background rates observed in unvaccinated populations.
“Oxford-AstraZeneca vaccine is effective against all severities of covid-19 and it plays a critical role in combatting the pandemic. Unless TTS was identified after the first dose, these results support the administration of the two-dose schedule of Oxford-AstraZeneca vaccine, as indicated, to help provide protection against covid-19 including against rising variants of concern," said Mene Pangalos, Executive Vice President, BioPharmaceuticals R&D.
The results are in line with recent reports in the Medicines and Healthcare products Regulatory Agency (MHRA) Yellow Card Report, the UK system for collecting and monitoring information on safety concerns, which also show low rates of TTS after a second dose, the British-Swedish drugmaker said.
“No specific risk factors or definitive cause for TTS following covid-19 vaccination have been identified and AstraZeneca continues to perform and support ongoing investigations of potential mechanisms. Furthermore, these very rare events can be avoided when symptoms are identified and treated appropriately," the company said in a statement.