Rates of the very rare clotting disorder, thrombosis with thrombocytopenia syndrome (TTS), following a second dose of AstraZeneca’s COVID-19 Vaccine are comparable to the background rate in an unvaccinated population.
The data, published in The Lancet on July 28, demonstrated the estimated rate of TTS following a second dose of AstraZeneca’s COVID-19 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.
Sir Mene Pangalos, Executive Vice President, BioPharmaceuticals R&D, said: “AstraZeneca’s COVID-19 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 AstraZeneca’s COVID-19 Vaccine, as indicated, to help provide protection against COVID-19 including against rising variants of concern.”
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. 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 AstraZeneca’s COVID-19 Vaccine.
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.
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.3
COVID-19 Vaccine (ChAdOx1-S [recombinant])
COVID-19 Vaccine (ChAdOx1-S [recombinant]) was co-invented by the University of Oxford and its spin-out company, Vaccitech. It uses a replication-deficient chimpanzee viral vector based on a weakened version of a common cold virus (adenovirus) that causes infections in chimpanzees and contains the genetic material of the SARS-CoV-2 virus spike protein. After vaccination, the surface spike protein is produced, priming the immune system to attack the SARS-CoV-2 virus if it later infects the body.
The vaccine has been granted a conditional marketing authorisation or emergency use in more than 80 countries across six continents. More than 800 million doses of COVID-19 Vaccine AstraZeneca have been supplied to more than 170 countries worldwide, including more than 100 countries through the COVAX Facility.
The WHO EUL was based on pooled analysis for efficacy from 11,636 participants aged 18 years and older, accruing 131 symptomatic COVID-19 infections from the UK and Brazil Phase III trials conducted by Oxford University. 5
Overall safety was based on an interim analysis of pooled data from four clinical trials conducted in the UK, Brazil and South Africa which included 23,745 participants aged 18 years or older. COVID-19 Vaccine (ChAdOx1-S [recombinant]) was well tolerated and there were no serious safety events confirmed related to the vaccine. The participants were from diverse ethnic and geographic groups who were healthy or had stable underlying medical conditions.
In the Philippines, the COVID-19 Vaccine (ChAdOx1-S [recombinant]) COVAX Supply has been given ‘emergency use listing’ by the World Health Organization. Similarly, the direct supply has been granted Emergency Use Authorization (EUA) by the Philippine Food and Drug Administration (FDA). This means that there is more evidence to come about this medicine. The World Health Organization and the Philippine FDA will review new information on this medicine as it becomes available and the leaflet will be updated as necessary. Please also note that the vaccine cannot be marketed or sold, advertised, and promoted.