With the U.S. vaccinating millions of people per day and racing against new COVID-19 variants, a fourth shot looks to be on its way.
In a phase 3 trial in the U.S., Peru and Chile, AstraZeneca’s vaccine—which is authorized in Europe and many other countries but not yet in the U.S.—posted 79% overall efficacy against symptomatic COVID-19. The shot also showed 100% protection against severe disease, hospitalization and death. In participants over 65, its efficacy rang in at 80%, even better than the overall figure.
The data win is no doubt welcome at AZ, which has been scrambling to fill vaccine orders in Europe and working to tamp down fears of a link between its vaccine and dangerous blood clots in a small number of recipients. The U.S. study could provide some help there—it found no evidence of an increased risk of blood clots among trial participants.
The newly reported trial enrolled 32,449 participants, and investigators randomized twice as many participants to receive vaccines as placebo. The trial used a four-week interval for the vaccine’s two doses, but other trials have showed better results at longer dosing intervals, such as 12 weeks.
The results show the vaccine is “highly effective and safe,” meaning it will play a growing role in fighting the pandemic, AstraZeneca's biopharmaceuticals executive vice president Ruud Dobber, Ph.D., said during a Monday press briefing. The company expects to submit its vaccine to the FDA in the first half of April, he said, and expects to roll out 30 million doses quickly if it's authorized.
Further, within the first month after authorization, the company would deliver another 20 million doses, Dobber said. AZ and its partners would then follow with an average of 15 million to 20 million doses per month after that. U.S. supply will be produced in the U.S., Dobber said—insulating it from the supply shortfalls elsewhere.
In Europe, where AZ had planned to depend on regional manufacturing, trouble at one plant has hamstrung supply and forced big cutbacks in its delivery goals. The supply constraints have caused an uproar in the EU, including moves to stop exports from regional plants to countries outside the bloc.
Meanwhile, concerns over blood clots caused several countries to halt distribution. Last week, European officials stood by the vaccine’s safety and efficacy after an urgent safety review, but they said they couldn’t rule out a link to rare blood clots.
Instead, the European Medicines Agency moved to raise awareness of the potential side effect. At a press briefing, the agency's executive director, Emer Cooke, said that with more awareness, people can “spot and mitigate” any possible side effects. The agency is launching “targeted observational studies” to learn more about the shot, Cooke said.
In the U.S. study, investigators didn’t find any increased risk of blood clots. In a specific search for cerebral venous sinus thrombosis among 21,583 vaccine recipients, the researchers turned up no cases.
Before the results from the current study, AstraZeneca had run a large phase 3 trial that created questions about dosing. In that trial, vaccine efficacy in participants who received two full doses came in at 62%. Efficacy for participants who received a half-dose for their first immunization came in at 90%. The new trial measured two full doses.
So far, based on other studies, the shot is authorized in around 70 countries. The shot also scored backing from the World Health Organization, allowing for delivery in many other countries.
Other than the AZ program, vaccines from Pfizer, Moderna and Johnson & Johnson have scored U.S. emergency use authorizations.