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March 22, 2021

AstraZeneca's COVID-19 vaccine found to be safe and 79% effective in U.S. trial

Several European countries recently suspended its use, but the study found it does not increase the risk of blood clots

Prevention Vaccines
AstraZeneca COVID-19 vaccine Yin-Shan Chiang/SOPA Images/Sipa USA

AstraZeneca's coronavirus vaccine was found in Phase 3 trials to be 79% effective at preventing symptomatic illnesses and 100% effective at stopping severe complications and hospitalizations caused.

AstraZeneca will submit its coronavirus vaccine to the U.S. Food and Drug Administration for an emergency use authorization in the coming weeks after a clinical trial found it to be effective and well-tolerated across all adult age groups and ethnicities. 

Data from the company's Phase 3 trials in the U.S. found the two-dose vaccine to be 79% effective at symptomatic illness and 100% effective against severe complications and hospitalizations. It also is 80% effective among seniors ages 65 and older.

"These findings reconfirm previous results observed in AZD1222 trials across all adult populations but it's exciting to see similar efficacy results in people over 65 for the first time," co-lead Principal Investigator Ann Falsey said. "This analysis validates the AstraZeneca COVID-19 vaccine as a much-needed additional vaccination option, offering confidence that adults of all ages can benefit from protection against the virus.”

An independent data safety monitoring board found no safety concerns in its review of the vaccine, including no increased risk of blood clots or thrombotic events among the 21,000-plus participants who received at least one dose.

Some Europeans who have received the vaccine developed blood clots, prompting several countries to suspend distribution. An emergency investigation by European regulators found the vaccine to be "safe and effective" and "not associated" with the blood clots. Regulators have urged countries to continue administering the vaccine.

Of the over 32,4000 people who participated in the U.S. trial, 141 symptomatic COVID-19 cases were discovered. Two-thirds of the participants received the vaccine, the others received a placebo. 

Senior citizens made up about 20% of the study's participants. Roughly 60% of participants had underlying health conditions associated with an increased risk for severe COVID-19 symptoms. 

"These results add to the growing body of evidence that shows this vaccine is well tolerated and highly effective against all severities of COVID-19 and across all age groups," AstraZeneca Executive Vice President Mene Pangalos said. "We are confident this vaccine can play an important role in protecting millions of people worldwide against this lethal virus."

AstraZeneca's COVID-19 vaccine was administered in two doses to participants over a four-week period.

However, previous clinical trials have found the company's vaccine to be more effective against COVID-19 when the doses are administered over an extended interval of up to 12 weeks. This timeline would allow for more people to receive their first COVID-19 shots sooner.

Research also suggests that AstraZeneca's vaccine has the ability to reduce transmission of the coronavirus.

AstraZeneca's COVID-19 vaccine, which was developed alongside the University of Oxford, can be stored at normal refrigerated conditions for at least six months and administered without needing to be prepared within an existing health care setting.

If authorized, AstraZeneca would join Pfizer, Moderna and Johnson & Johnson as the COVID-19 vaccines currently available in the U.S. The U.S. has agreed to buy 300 million doses of AstraZeneca's COVID-19 vaccine once it is authorized. 


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