AstraZeneca COVID-19 vaccine US trial: 79% effective with no extra blood clot risk

AstraZeneca's COVID-19 vaccine is effective at preventing coronavirus, a new US study has concluded, with 100-percent efficacy against severe or critical cases, or hospitalization. The study of the AZD1222 vaccine candidate, which is not currently authorized in the US for immunizations, showed 79-percent efficacy at preventing symptomatic COVID-19.

The Phase 3 study included 32,449 participants, and used a 2:1 randomization of vaccine to placebo. Overall, there were 141 symptomatic cases of COVID-19 recorded across the participants in the trial.

Like the Moderna and Pfizer vaccines already in deployment in the US, the AstraZeneca drug – co-developed by the University of Oxford and Vaccitech – consists of two doses. They're administered at a four week interval, though previous trials have indicated there's the potential for even greater results if that interval is extended, to up to 12 weeks apart. "This evidence suggests administration of the second dose with an interval longer than four weeks could further increase efficacy and accelerates the number of people who can receive their first dose," AstraZeneca pointed out today.

As for storage and transportation, the vaccine can be shipped and handled at normal refrigerated conditions, typically 2-8 degrees Celsius or 36-46 degrees Fahrenheit, for "at least six months," the company says. There's no unusual preparation required which could make it tricky to administer within existing healthcare settings, AstraZeneca adds.

"Vaccine efficacy was consistent across ethnicity and age," the drug company points out. "Notably, in participants aged 65 years and over, vaccine efficacy was 80%."

For side-effects, there was no sign of increased thrombosis risk, or events characterized by thrombosis, among the 21,583 participants who received at least one dose of AZD1222. It follows concerns in Europe around the vaccine, which had been linked earlier this month to a reported uptick in blood clot incidents. This study, meanwhile, also found no incidents of cerebral venous sinus thrombosis (CVST) among trial participants.

"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," Mene Pangalos, Executive Vice President, BioPharmaceuticals R&D, said today of the findings. "We are confident this vaccine can play an important role in protecting millions of people worldwide against this lethal virus. We are preparing to submit these findings to the US Food and Drug Administration and for the rollout of millions of doses across America should the vaccine be granted US Emergency Use Authorization."

That submission should take place "in the coming weeks," AstraZeneca says. At the same time, it's also preparing the results of the study for publication in a peer-reviewed journal. AZD1222 is already being used in 70+ countries worldwide. It was granted Emergency Use Listing by the World Health Organization.