Detailed data on AstraZeneca-Oxford Covid-19 vaccine show it has moderate efficacy

The Covid-19 vaccine being developed by the University of Oxford and AstraZeneca appears to have moderate efficacy in preventing symptomatic illness, and may significantly reduce hospitalization from the disease, data from four clinical trials of the vaccine reveal.

Topline data on the vaccine from a Phase 3 trial were released in November. The new data, published Tuesday in The Lancet, draw from trials in various phases and include safety data on more than 20,000 participants.

The data confirm that two standard doses of the vaccine were 62% effective in preventing symptomatic Covid-19 disease in some trials. But when data from all four trials were pooled — including trials in which volunteers received a low dose followed by a standard dose of vaccine — the vaccine had 70% efficacy.


Among only volunteers who received a low dose followed by a standard dose of vaccine, the vaccine had 90% efficacy.

It’s still not clear why efficacy in this group — which did not include anyone over the age of 55 — was so high. AstraZeneca is still deliberating whether to conduct another trial to explore using this dosing regimen, Mene Pangalos, AstraZeneca’s executive vice president for biopharmaceuticals R&D, said Tuesday during a press briefing.


Pangalos said AstraZeneca is submitting its data on a rolling basis to regulatory agencies in multiple countries around the world and expects that the data generated so far will be sufficient to win regulatory approval for the vaccine. The company expects, though, that the Food and Drug Administration will require AstraZeneca to complete its ongoing U.S.-based trial before considering issuing an emergency use authorization for the vaccine in this country.

The Lancet publication pooled data from Phase 1/2 and Phase 2/3 in the United Kingdom, a Phase 3 trial in Brazil and a Phase 1/2 trial in South Africa.

There were three severe adverse events reported, two of which may have been related to receipt of the vaccine. (One was in the control arm.) One person developed transverse myelitis, a rare but potentially serious neurological condition. This person, whose case was previously reported, received the vaccine.

Another person developed a high fever of over 104 degrees Fahrenheit after receiving the first dose of vaccine. The fever quickly resolved and the individual continued in the trial. Whether that person received the vaccine or a placebo is still not known; his or her vaccine status is still blinded.

The efficacy data was based on 11,636 participants.

There were no cases of severe disease or hospitalization among people in the vaccine arms of the trials from three weeks after they receive their first dose — an intriguing finding. Among placebo recipients, there were 10 people who were hospitalized for Covid-19 after the first dose; two were classified as severe and one of those people died.

The differential in the results between the two dosing regimens has puzzled vaccine experts, some of whom remain unconvinced the effect was real and not a result of statistical chance.

Nahid Bhadelia, medical director of the special pathogens unit at Boston Medical Center, said more study of the low dose, standard dose regimen is warranted.

“There’s a marginal cost of waiting, but there is a marginal cost of vaccinating people with what turns out to be a less efficacious strategy. What if low-dose standard-dose is the way to go?” she asked.

The Oxford-AstraZeneca vaccine is inexpensive to make and can be stored at refrigerator temperature — a major advantage over the messenger RNA vaccines being developed by Pfizer and Moderna, the vaccine race frontrunners. As such, there much hope has been placed on this vaccine supplying many low- and middle-income countries.

Matthew Herper contributed reporting.

Source: STAT