Rochester, NY—Emergency-use authorization is likely to be sought late this month or in early April for another COVID-19 vaccine. But, because of some unproven safety concerns raised about the AstraZeneca vaccine in Europe and elsewhere and because the supply of product from three other manufacturers is rapidly increasing in the United States, having a fourth vaccine online might not make that much difference to the nation’s immunization efforts.

The U.S. phase III trial of AstraZeneca’s vaccine, AZD1222, which was developed with the University of Oxford in the United Kingdom, demonstrated vaccine efficacy at preventing symptomatic COVID-19 of 76% (confidence interval [CI], 68%-82%) occurring 15 days or more after receiving two doses given 4 weeks apart. AstraZeneca also emphasizes that results were comparable across age groups, with vaccine efficacy of 85% (CI, 58%-95%) in adults aged 65 years and older. The vaccine was found to be 100% effective in meeting an important secondary endpoint, preventing severe or critical disease and hospitalization. All eight cases of severe COVID-19 observed in the primary analysis occurred in the placebo group, according to a press release

This primary efficacy analysis included the accrual of 190 symptomatic cases of COVID-19 from the 32,449 trial participants, an addition of 49 cases to the interim analysis that had been announced several days before and had been questioned by the National Institute of Allergy and Infectious Disease. The National Institutes of Health Agency raised concerns that the information was outdated.

“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. 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,” said colead principal investigator Ann Falsey, MD, of the University of Rochester School of Medicine.

After questions were raised about whether the data was outdated, AstraZeneca said, “Positive high-level results from the primary analysis of the Phase III trial of AZD1222 in the U.S. have confirmed vaccine efficacy consistent with the pre-specified interim analysis announced on Monday March 22, 2021.”

Most of the participants in the interim analysis, 79%, were white/Caucasian, 8% black/African American, 4% native American, 4% Asian, and 22% of participants were Hispanic. About 20% of participants were aged 65 years and older, and approximately 60% had comorbidities associated with an increased risk for progression of severe COVID-19, such as diabetes, severe obesity, or cardiac disease.

Safety results were closely watched. AstraZeneca reports that the vaccine was well tolerated, and the independent data safety monitoring board identified no safety concerns related to the vaccine. A specific review of thrombotic events, as well as cerebral venous sinus thrombosis, was conducted with the assistance of an independent neurologist, according to the report, but no increased risk of thrombosis or events characterized by thrombosis was found among the 21,583 participants receiving at least one dose of the vaccine.

A statement from the European Medicines Agency (EMA) last week stated, “the [AstraZeneca] vaccine is not associated with an increase in the overall risk of blood clots.” But that finding came after more than a dozen countries had halted vaccinations with the products because of reports of rare clotting problems linked to low blood platelets in recipients.

On the other hand, the EMA pointed out that around 20 million people had received the vaccine as of mid-March, and only about 30 cases of blood clotting issues were reported. It added that the number of reports of those rare clotting problems “exceeds those expected, and causality although not confirmed, cannot therefore be excluded,” according to the statement, which noted that labeling on the vaccine will be updated to include more information about the events.

As for the U.S., which is using other vaccines, AstraZeneca has agreements with the U.S. government to deliver 300 million doses, according to what the company told Congress in February. Earlier in March, the White House COVID-19 coordinator said the U.S. would have more than enough vaccine doses with supply from Pfizer, Moderna, and Johnson & Johnson to vaccinate every American adult by the end of May.

This AstraZeneca–led U.S. phase III trial included two doses administered at a 4-week interval. The vaccine can be stored, transported. and handled at normal refrigerated conditions (2-8 degrees Celsius or 36-46 degrees Fahrenheit) for at least 6 months and administered without the need for preparation within existing healthcare settings.

Company officials said they are preparing to file for the EUA from the FDA.

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