| Daily Briefing

Is AstraZeneca's vaccine safe and effective? Here's what a major study just revealed.

AstraZeneca on Monday released preliminary clinical trial data on its Covid-19 vaccine candidate that showed the inoculation is safe and effective at preventing asymptomatic and severe cases of the disease, setting the stage for the company to seek FDA's authorization for the vaccine.

The new data comes after numerous countries last week suspended the use of the vaccine, which AstraZeneca developed with the University of Oxford, due to a small number of reports of blood clots among those who had received the inoculation.

However, the European Union's drug regulator, called the European Medicines Agency (EMA), and the World Health Organization (WHO) have said there is little reason to believe the vaccine caused the blood clots, which can occur by chance in otherwise healthy populations. Most countries have since resumed administering the vaccine.

Editor's note: The National Institute of Allergy and Infectious Diseases in a statement early on March 23 said AstraZeneca may have released "outdated information" on its Covid-19 vaccine that "may have provided an incomplete view" of the vaccine's effectiveness. AstraZeneca responded that the numbers "were based on a pre-specified interim analysis" and that it would "immediately engage with the independent Data Safety Monitoring Board to share our primary analysis with the most up to date efficacy data."

Data shows AstraZeneca's Covid-19 is safe and effective

The new data is from a large-scale clinical trial. For the trial, researchers recruited and enrolled more than 32,000 participants from Chile, Peru, and the United States to test the vaccine candidate's effectiveness and safety.

Among the trial's participants, approximately 79% were white, 22% were Hispanic, 8% were Black, 4% were Native American, and 4% were Asian. Roughly 20% of participants were ages 65 and older, and about 60% had comorbidities—including cardiac disease, diabetes, and severe obesity—associated with severe cases of Covid-19. The participants received either two shots of the vaccine candidate or two saline shots administered four weeks apart.

Overall, the vaccine was 79% effective in preventing symptomatic cases of Covid-19, the New York Times reports. The vaccine's "efficacy was consistent" among participants of all ages and ethnicities, AstraZeneca said in the release. The data, for example, showed the vaccine was 80% effective among participants ages 65 and older.

The vaccine also was 100% effective in preventing severe cases of Covid-19 and hospitalizations—with no severe cases or hospitalizations occurring among the participants who had received the vaccine, according to the release. However, it's difficult determine whether those findings represent a statistically significant reduction in risk compared to a placebo, because AstraZeneca did not release data on the number of placebo recipients who developed severe cases of Covid-19 or had to be hospitalized, the Times reports.

In terms of safety, the data showed no increased risk of blood clots or related events among the 21,583 participants who received at least one dose of the vaccine. The data also showed no cases of serious neurological problems. And when researchers reviewed their data for evidence of blood clots in the brain—which have been reported among vaccine recipients in Europe—they found no cases, according to the release.

AstraZeneca in the release said it "will continue to analyze the data and prepare for the primary analysis to be submitted to [FDA] for [an EUA] in the coming weeks."

According to experts, any authorization in the United States likely wouldn't happen until May, when federal officials project the United States will have enough vaccine doses for all American adults from the three manufacturers who already offer authorized vaccines. As a result, AstraZeneca's vaccine is expected to have a minimal effect on America's Covid-19 vaccine rollout, the Times reports.

Experts say the data is reassuring but want more details

Many experts said the new data is reassuring amid the concerns about the vaccine's safety.

In the release, Ann Falsey, a professor of medicine at the University of Rochester School of Medicine and co-lead principal investigator for the clinical trial, 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."

Similarly, Paul Hunter, a professor of medicine at the University of East Anglia, said the preliminary results are encouraging, but more information is needed to confirm the vaccine's effectiveness at preventing severe cases of Covid-19 and hospitalizations.

"It would be good to know how many severe cases occurred in the control group and so what the confidence intervals are for this 100% figure," Hunter said. "But this should add confidence that the vaccine is doing what it is most needed for."

Stephen Evans, of the London School of Hygiene & Tropical Medicine, said, "The benefits of these results will mainly be for the rest of the world, where confidence in the … vaccine has been eroded, largely by political and media comment" (Robbins/Mueller, New York Times, 3/22; Strasburg, Wall Street Journal, 3/22; Cheng/Neergaard, Associated Press, 3/22; Herper, STAT News, 3/22; Joseph, STAT News, 3/20; New York Times, 3/15; Anderson, Becker's Hospital Review, 3/19).

Advisory Board's take

4 questions we're considering after AstraZeneca's encouraging new vaccine data

By Pamela Divack, Senior Analyst, and Brandi Greenberg, Vice President of Life Sciences and Ecosystem Research

Overall, the new data from AstraZeneca is encouraging. The results shared in the press release—including the 79% efficacy against symptomatic Covid-19, the lack of major safety concerns, and the 100% efficacy against severe disease—represent great news for AstraZeneca and the future of vaccine rollouts across the world.

As we await further data and the full peer-reviewed analysis from AstraZeneca and Oxford, here are four questions and issues we are watching:

  1. How well does the vaccine work against known variants? The data shared this morning did not provide insight into how well the vaccine works against variants of Covid-19 and did not provide a breakdown of efficacy by country. That data will provide key insight into the vaccine's effectiveness against variants—and might even help guide future vaccine deployment and allocation efforts across the globe.


  2. How well does the vaccine work in different patient demographics and subpopulations? AstraZeneca's study was slightly less racially and ethnically diverse than other Phase 3 vaccine trials for Covid-19. Participants were 79% white, 22% Hispanic or Latino, 8% Black, 4% Native American, and 4% Asian. In addition, 20% of participants were 65+ years old and 60% had comorbidities. In the coming weeks, we'll be looking for additional data that assesses efficacy in these different populations.


  3. Will the U.S. really need AstraZeneca's vaccine by the time it is authorized? Given the accelerating pace of the vaccine rollout in the United States and lingering pockets of hesitancy, it's possible that the steady supply of Pfizer, Moderna, and J&J's vaccines will exceed weekly demand for vaccines in the U.S. by the late spring. The U.S has already agreed to share 4 million doses of AstraZeneca's vaccine with Mexico and Canada, but some experts are calling for the U.S. to donate even more supply to other countries, recognizing the potential for excess. However, the implications of this remain unclear.


  4. Will an emergency use authorization for AstraZeneca's vaccine increase patients' likelihood to vaccine shop for the brands they perceive to be the "best"? Across the country, vaccine sites are increasingly transparent in telling the public which vaccine they offer and when. Given recent confusion over the AstraZeneca vaccine's safety in other parts of the world, it's likely that some patients might opt for a vaccine other than AstraZeneca's, if given the ability to choose (and if the vaccine is authorized).

Communication about the vaccine will be essential to building public confidence and trust

AstraZeneca's previous trial and rollout pauses—including February's trial halt in South Africa due to concerns about the efficacy against new variant, last September's trial pause due to a unexplained illness, and last week's rollout pauses in the EU due to blood clot concerns—have exacerbated skepticism and confusion about vaccines.

If FDA authorizes AstraZeneca's vaccine , providers and public health agencies will need to play an active role in communicating information about the vaccine to the public and clarifying existing questions and confusion. They also will need to collect ongoing real-world data that confirms the latest results and provides additional confidence in today's data.






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