New AstraZeneca Data Show Vaccine 76% Effective at Preventing Symptomatic COVID-19

AstraZeneca’s COVID-19 vaccine is not been authorized for use in the U.S. but is being widely used in Europe. Manuel Dorati/Anadolu Agency via Getty Images

AstraZeneca released updated details of its latest clinical trial results…

AstraZeneca's COVID-19 vaccine is not been authorized for use in the U.S. but is being widely used in Europe. Manuel Dorati/Anadolu Agency via Getty Images
  • AstraZeneca released updated details of its latest clinical trial results, after a U.S. safety board raised concerns that data released earlier in the week may have been “outdated.”
  • Results published on March 25 were based on an analysis of data from the phase 3 clinical trial, which included more than 32,000 participants in the United States, Chile, and Peru.
  • The company plans to request emergency approval of its COVID-19 vaccine in the coming weeks.

Vaccine maker AstraZeneca released updated details about how well its coronavirus vaccine works. The vaccine showed 76 percent efficacy against symptomatic coronavirus infection, the company said Wednesday in a statement.

The vaccine also showed 100 percent efficacy against severe or critical disease or hospitalization, and 85 percent overall efficacy in people 65 years or older, the company said.

The results were similar to what the company announced in a statement Monday. 

As before, the results were announced in a news release, so details are sparse. They have also not been peer-reviewed or reviewed by Food and Drug Administration scientists.

“The primary analysis is consistent with our previously released interim analysis, and confirms that our COVID-19 vaccine is highly effective in adults, including those aged 65 years and over,” Mene Pangalos, executive vice president for biopharmaceuticals research for the company, said in the news release.

The company said it plans to submit an application for emergency approval to the FDA in the coming weeks.

FDA scientists will review the company’s data in depth and present its analysis to the advisory committee that has reviewed the other COVID-19 vaccine applications.

The company also plans to submit its full analysis to a peer-reviewed journal for publication.

Safety board raised concerns about data

On Tuesday, an independent U.S. safety board overseeing the vaccine trial raised concerns about the information released the day before by AstraZeneca.

The Data and Safety Monitoring Board (DSMB) was concerned that the company may have included “outdated information” that could give an “incomplete view” of the vaccine’s efficacy, according to a statement released early March 23 by the National Institute of Allergy and Infectious Diseases (NIAID).

The NIAID urged AstraZeneca to work with the DSMB to review the data, and make sure the “most accurate, up-to-date efficacy data” is shared with the public as soon as possible.

The earlier release by the company said that the vaccine showed 79 efficacy against symptomatic infection, and 100 percent efficacy against severe or critical disease and hospitalization.

The phase 3 vaccine trial included more than 32,000 adults in the United States, Chile, and Peru. Participants received either two doses of the vaccine given 4 weeks apart, or an inactive placebo given at the same interval.

The most recent analysis included 190 cases of symptomatic COVID-19, with most of the cases occurring in people who received the placebo.

“There are 14 additional possible or probable cases” that may be included in the total when the company submits its data to the FDA, the company said in its statement. So the final efficacy could change.

Dr. Anthony Fauci, the head of the NIAID, said Tuesday on “Good Morning America” that what happened was unfortunate, calling it an “unforced error” by the company.

“The data are really quite good,” Fauci said, “but when [the company] put it into the press release, it wasn’t completely accurate.”

On Twitter, Saad B. Omer, PhD, director of the Yale Institute for Global Health, raised a common concern among clinical trial scientists about this type of public announcement by companies.

“Say it with me: data sharing through press release (without any additional material e.g. a slide set, preprint etc.) is not a good idea,” he wrote.

Fauci added that the vaccine review process includes many safeguards — including the DSMB — that ensure that vaccines approved by the Food and Drug Administration (FDA) are safe and effective.

Study found no blood clotting concerns

AstraZeneca’s COVID-19 vaccine, which was developed with the University of Oxford, has been under scrutiny recently after several European countries temporarily halted its rollout after reports of blood clotting in some people who had received the vaccine.

Following an emergency investigation, the European Medicines Agency (EMA) said on March 18 that the vaccine’s benefits outweigh the risks, and concluded that the vaccine is “not associated with an increase in the overall risk of blood clots, or thromboembolic events.”

However, the agency said “the vaccine may be associated with very rare cases of blood clots.” The agency will continue to watch for any connection between the vaccine and blood clotting disorders.

Germany, France, Italy, and Spain have since said they would resume the rollout of the AstraZeneca vaccine, reports BBC News

However, Denmark officials decided Thursday to extend their suspension of the vaccine’s rollout as health officials there evaluate a potential link between the vaccine and blood clotting, according to ABC News.

In response to blood clotting concerns, the DSMB and an independent neurologist carried out a more specific review of the new clinical trial data, looking for blood clotting events, including a type of brain clot called a cerebral venous sinus thrombosis.

They found no increased risk of blood clotting among the more than 21,000 trial participants who had received at least one dose of the vaccine.

Certain rare events, though, may not show up during a clinical trial. This is why the FDA and the Centers for Disease Control and Prevention (CDC) continue to monitor the safety of vaccines after they’re released.

In its press release, AstraZeneca said the vaccine was “well tolerated” by people who received it, and “no safety concerns related to the vaccine” were identified by the DSMB.

Of the participants included in the interim analysis, about 79 percent were white, 22 percent were Hispanic, 8 percent were Black, 4 percent were Native American, and 4 percent were Asian.

Around 20 percent of people in the trial were 65 years or older, and about 60 percent had health conditions linked to a higher risk of severe COVID-19, such as diabetes, severe obesity, or heart disease.

The high overall efficacy for participants 65 years or older is welcome news. Some countries that approved the AstraZeneca vaccine had initially excluded older adults from vaccination due to a lack of data on this age group in earlier trials.

Although AstraZeneca’s overall efficacy is lower than that of the Pfizer-BioNTech and Moderna vaccines, it compares favorably in terms of protecting against severe disease and hospitalization.

However, it’s difficult to directly compare the vaccines, because the clinical trials used different criteria for how to measure the outcome.

The studies were also done in different countries at different times, and with different SARS-CoV-2 variants circulating.

The results of a previous trial, published in The Lancet, suggest that waiting up to 12 weeks before giving the second dose may boost the vaccine’s efficacy.

Vaccine may help lower-income countries most

The AstraZeneca vaccine has already been approved in more than 70 countries, the company said.

If the FDA approves the vaccine, it will bring the number of approved vaccines in the United States to four.

However, “we’re going to have millions more doses of the three licensed [vaccines] in the United States by the spring,” Dr. Sarah George, associate professor of infectious diseases at Saint Louis University School of Medicine. “So by the time [the AstraZeneca vaccine] does go through the FDA approval process, there may not be as much use for it in this country.”

The vaccine can still help other countries vaccinate their population, especially those that have been largely shut out of access to COVID-19 vaccines.

Higher-income countries such as the United States make up just a fifth of the global adult population, but they have purchased more than half of all vaccine doses, reports the Kaiser Family Foundation.

The United States has already agreed to send 4 million doses of the AstraZeneca vaccine that it’s not using to Canada and Mexico.

The AstraZeneca vaccine’s less rigorous storage requirements will make it easier to distribute in areas of the world without reliable access to freezer storage. It can be stored at normal refrigerator temperatures for at least 6 months.

“Cold-chain monitoring, as it is called, is a real issue with vaccines,” said George, “particularly in parts of the world where electricity supplies are minimal or not reliable.”

Both the Pfizer-BioNTech and Moderna vaccines need to be stored in a freezer until they’re thawed before use.