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Update (March 23): The US National Institutes of Allergy and Infectious Diseases’s Data Safety Monitoring Board “expressed concern that AstraZeneca may have included outdated information from that trial, which may have provided an incomplete view of the efficacy data,” NIAID said in a statement today. AstraZeneca responded in its own statement that the data came from a prespecified interim analysis and that the company “will immediately engage with the independent data safety monitoring board (DSMB) to share our primary analysis with the most up to date efficacy data.”

No recipients of Oxford/AstraZeneca’s COVID-19 vaccine developed serious symptoms or went to the hospital because of a SARS-CoV-2 infection, indicating the immunization may completely protect against severe disease, according to data from a Phase 3 trial conducted in the US, Chile, and Peru. The two-dose immunization was also 79 percent effective at preventing symptomatic cases, the company announced in a press release today (March 22).

“Seeing this data now I hope gives others increased confidence that this is a very effective and safe vaccine,” Mene Pangalos, an AstraZeneca executive vice president, told reporters at a press conference, according to Reuters. 

The company expects to apply for emergency use authorization in the US in April, Reuters reports. The vaccine is already in use in numerous countries around the globe. 

Concerns about the risk of blood clots resulting from the vaccine led some of those nations to pause distribution this month, but after reassurance from the World Health Organization and the European Medicines Agency last week that there is no increased risk of thrombosis, many countries have resumed rollout. AstraZeneca reported no elevated risk of blood clots among those who received the shots in its Phase 3 study.

The trial included more than 32,000 participants—two-thirds of whom received the vaccine, while one-third got a placebo—and 141 individuals developed COVID-19 in total. There didn’t appear to be differences in efficacy between racial or age groups.

“And that was the extent of hard data reported in the company’s press release,” MedPage Today notes. “It did not indicate the time frame for dosing and follow-up, stratification of results by sex, nor effectiveness against virus variants of concerns such as B.1.1.7 or B.1.351 (the U.K. and South African strains, respectively).”

The vaccine delivers the gene for SARS-CoV-2’s spike protein using a chimpanzee adenovirus vector. The Washington Post notes that it has the advantage of being stored in a regular refrigerator, rather than in freezers as Pfizer’s and Moderna’s vaccines do, and is comparatively cheap at $4 a dose. The other two cost at least $30 for the two-dose regimen.

See “Vector-Based Vaccines Come to the Fore in the COVID-19 Pandemic”

According to the Post, the US has preordered 300 million doses of AstraZeneca’s shots.