In the Lancet, the AstraZeneca and Oxford scientists report on the interim results from two clinical trials run Britain and Brazil, involving 11,636 participants who got the vaccine, half to got the vaccine and half who received a placebo.
It is described as the first full peer-reviewed efficacy results to be published for a COVID-19 vaccine.
During the trial, only three people out of the 23,745 participants over a median of 3.4 months experienced any adverse events that could have been related to the vaccine.
In the control group - those who did not receive AZD1222 - ten participants were hospitalised due to COVID-19, with two volunteers developing severe disease, including one fatal case.
"I would wait until at least the US trial, which is much more tightly controlled in terms of dosing and intervals between doses, reads out before approving the vaccine", said Fazeli.
In an editorial published with the study, Maria Deloria Knoll, PhD, and Chizoba Wonodi, MBBS, of Johns Hopkins Bloomberg School of Public Health, Baltimore, wrote that the lower cost (U.S. $2-3 per dose) and easier storage of the ChAdOx1 nCoV-19 vaccine "holds good promise for equitable access for low income and middle income countries, compared with the high cost of the two mRNA vaccines that have reported more than 90% efficacy". It plans to dispense 800,000 doses of the Pfizer/BioNTech vaccine in the coming weeks.
Still, experts say the vaccine seems likely to be approved, despite some confusion in the results and lower levels of protection than what some other vaccine candidates have shown. This pandemic in 2009 saw social and racial inequalities being practically ignored in the process of vaccine distribution, leading to disproportionate rates of Black and Hispanic people in the U.S. being hospitalized and dying from swine flu.
There are still important questions about what dose would be best, as well as the age group it will protect the most.
"We have begun submitting data to regulatory authorities around the world for early approval and our global supply chains are up and running, ready to quickly begin delivering hundreds of millions of doses on a global scale at no profit".
Pfizer and BioNTech have reported more than 90% efficacy of their COVID-19 vaccine "BNT162b2" while Moderna has claimed that its mRNA-1273 vaccine yielded 94.5% efficacy in early results.
"I'm absolutely not suggesting that the vaccine should be a one-dose vaccine", he said, though perhaps future studies could look at a one-dose regimen.
The Pfizer vaccine was approved for emergency use in Britain and the first injections in a massive campaign began Tuesday.
But the complexity of the trial, which used different dosages, different intervals between the first and second shot and different control groups may mean that more data needs to be gathered to understand to satisfy regulators.
The data is based on 11 636 volunteers across the United Kingdom and Brazil, and combined across three groups of people vaccinated - two groups who received a standard dose prime vaccination followed by a standard dose booster vaccination, and one group (in the United Kingdom only) who received a low dose prime vaccination followed by a standard dose vaccination. They are now both said to be recovering well.
"(This) will require further research as more data becomes available", the researchers said. Although these trials do have older participants, they were recruited later, so collection of efficacy data for this group is ongoing. "We've shown the vaccine is safe and well tolerated".