A Third Coronavirus Vaccine Trial Has Reported Promising — But Confusing — Results

The vaccine, which Oxford University developed alongside the company AstraZeneca, was reportedly highly effective in preventing hospitalizations or severe cases of the coronavirus.

A COVID-19 vaccine developed by the University of Oxford and AstraZeneca has shown "positive high-level results" in early data from clinical trials, researchers announced Monday. It is the third vaccine to report promising interim results, after Pfizer and Moderna.

The vaccine has been 70% effective on average so far, researchers said. But the early data came with a confusing caveat: The vaccine was 90% effective for volunteers who were given a half-dose of the vaccine followed by a full dose — a much higher success rate than those who were given two full doses, which was 62% effective.

That half dose was only given to participants because of a mistake in the British arm of the trial, Reuters reported. As a result, only a little over 2,700 people received the half-dose shot, out of the 23,000 people in the trial results reported Monday, a very small subset to base results on. Then, on Tuesday, Operation Warp Speed head Moncef Slaoui said the age of participants in the half-dose group was capped at 55, casting further doubts on the results. Scientists have since criticized AstraZeneca for both its trial design and how it disclosed its data, which have not yet been peer reviewed or released in full.

The early analysis was based on 131 COVID-19 cases among trial participants who either received the vaccine or a placebo injection.

The company said that the trials, which took place in the UK and Brazil, also showed that the vaccine was highly effective in preventing hospitalizations or severe cases of the coronavirus. “These findings show that we have an effective vaccine that will save many lives," professor Andrew Pollard, chief investigator of the Oxford vaccine trial, said in a press release.

Unlike the Pfizer and Moderna trials, which only tested people who reported symptoms, the AstraZeneca data also showed that asymptomatic infections were reduced in the group of patients who received a vaccine, suggesting that it can help limit transmission. The AstraZeneca trial in the UK swabbed patients weekly, which provided more information about who developed infections.

Earlier this month, Pfizer and Moderna announced that trials for their vaccines both suggest that they are more than 90% effective. The Food and Drug Administration requires a vaccine to be at least 50% effective before authorizing its use.

The Oxford-AstraZeneca vaccine is cheaper than the Pfizer or Moderna vaccines and may also be easier to store and transport.

AstraZeneca is requesting an "Emergency Use Listing" from the World Health Organization to make the vaccine quickly available in low-income countries. The company said it would begin discussions with the FDA this week about whether to formally submit for review in the US, but scientists have questioned whether the US health agency would accept their questionable results.

Researchers had to pause the vaccine's effectiveness study twice, a development which is not unusual in clinical trials. In July, a patient developed multiple sclerosis, and in September another patient developed a neurological illness called transverse myelitis. The vaccine was not found to have caused either illness, and the trials resumed, leading to today's preliminary results.

In its data release, the drug company said that "no serious safety events related to the vaccine have been confirmed."

In response to the company's announcement on Monday, Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told STAT that, "If it’s 70%, then we’ve got a dilemma."

“Because what are you going to do with the 70% when you’ve got two [vaccines] that are 95%? Who are you going to give a vaccine like that to?”


This story has been updated to include further details about the half-dose arm of the clinical trial.

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