AstraZeneca COVID-19 Vaccine Woes Continue as Questions are Raised over US Trial Data

Published on: 

After releasing US Phase III trial data for AZD1222, more questions have been raised with AstraZeneca concerning potentially outdated information that could provide an incomplete view of efficacy.

On March 22, 2021, AstraZeneca released US Phase III trial data for its COVID-19 vaccine, AZD1222, that the independent data safety monitoring board (DSMB) found to have potentially included outdated information from the trial, providing an incomplete view of the efficacy data.

The data showed a 79% vaccine efficacy at preventing symptomatic COVID-19, a 100% efficacy against severe or critical disease and hospitalization, comparable efficacy across ethnicity and age, with 80% efficacy in participants aged 65 years and over, and favorable reactogenicity and overall safety profile, AstraZeneca said in the March 22, 2021 press release. The trial included 32,449 participants, 141 of which had symptomatic cases of COVID-19.

Following the DSMB’s findings, AstraZeneca released a statement on March 23, 2021 that clarified the data released were based on a pre-specified interim analysis with a data cut-off of Feb. 17, 2021.

“We have reviewed the preliminary assessment of the primary analysis and the results were consistent with the interim analysis,” AstraZeneca said in a company press release. “We are now completing the validation of the statistical analysis.”

According to the statement, the company plans to share its primary analysis with the most up to date efficacy data with the DSMB within 48 hours.


The findings of the DSMB in the US add to the current woes for AstraZeneca, which is also dealing with rising belief among European populations that the vaccine is unsafe due to recent reports about blood clots in some recipients of the vaccine. According to the latest figures from YouGov, more people in Germany, France, Spain, and Italy now believe the AstraZeneca vaccine to be unsafe compared with those who believe it to be safe.

However, regulatory authorities in the United Kingdom and Europe have confirmed that the benefits of the AstraZeneca vaccine continue to outweigh the risk of side effects, with no causal link between the vaccine and thromboembolic events established.

Source: AstraZeneca (March 22, March 23), NIH, YouGov