Pfizer and BioNTech’s Covid-19 vaccine starts to work within about 10 days of the first dose, according to new documents released by the US regulator ahead of an advisory meeting this week to discuss whether to grant it emergency approval.
The report has raised hopes that the vaccine could start to help ease the pressures on overwhelmed hospitals soon after it is rolled out. It is already approved in the UK but will be the first to be considered for an emergency use authorisation in the US.
The Food and Drug Administration confirmed the vaccine shows a high efficacy rate of 95 per cent on average, with 93.8 per cent in participants over 55. The vaccine requires two shots, spaced 21 days apart. It is not yet clear how long the vaccine’s protection lasts.
The documents provide the most detailed data yet on participants, including showing that it worked well whatever their race, age or weight.
The regulator’s scientists did not raise any significant concerns about safety — although the report on Tuesday said there was not yet enough evidence about how safe it is in children, pregnant and breastfeeding women, as well as people with compromised immune systems, such as those with HIV. The most common side-effects are pain at the injection site, fatigue and headache.
There were more cases of Bell’s palsy, a muscular weakness in the face, and appendicitis in the group of people who received the vaccine than the group that received the placebo. But the FDA said the incidence was not higher than in the general population of the same ages.
There were four deaths in the placebo group and two in the vaccine group, at a similar rate to in the general population. With a trial of about 44,000, it is usual to see some death and serious illness.
The FDA’s advisory group on vaccines will meet publicly on Thursday to discuss whether the Pfizer/BioNTech vaccine should receive an emergency use authorisation.
The regulator is asking the advisers to consider whether it is reasonable to believe that the vaccine prevents Covid-19 in people aged 16 and over, and if the benefits outweigh the risks. The FDA is not bound by its advisers’ decisions.
Scientists said the vaccine would continue to be studied after emergency approval as it is rolled out in a broader population.
As well as monitoring for side-effects that may only show up in a larger group, the FDA suggested there should be further evaluations to see whether the vaccine could prevent asymptomatic Covid-19 infection. A significant number of people can spread the virus without suffering from symptoms.
The FDA warned that if participants immediately had a vaccination after an emergency approval, it could interfere with the ability to collect follow-up data. It said strategies should be considered to balance the need for this data with the ethical obligations to placebo recipients.
The documents said Pfizer would like to unblind the trial, giving the placebo participants the opportunity to have a vaccination. For the first six months after the second dose, this will only be for people who request the vaccine.