The results are based on the first interim analysis of Phase 3 of the study, and evaluated 94 confirmed cases of COVID-19 in trial participants.
The study enrolled 43,538 participants, including people with diverse racial backgrounds, and no serious safety concerns have been observed, the companies report. They add that safety and additional efficacy data continue to be collected.
The firms have not specified the ages of the participants.
The case split between vaccinated individuals and those who received the placebo indicates a vaccine efficacy rate above 90 per cent, at seven days after the second dose. Researchers say this means that protection is achieved 28 days after the initiation of the vaccination, which consists of two doses.
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“We will continue to collect further data as the trial continues to enrol for a final analysis planned when a total of 164 confirmed COVID-19 cases have accrued,” said Dr Albert Bourla, Pfizer chairman and chief executive. “The first set of results from our Phase 3 COVID-19 vaccine trial provides the initial evidence of our vaccine’s ability to prevent COVID-19.”
The researchers caution that as the study continues the final vaccine efficacy percentage may vary.
“This cautiously sounds like an excellent result from the Phase 3 trials, but we should remain a little cautious,” said Dr Michael Head, Senior Research Fellow in Global Health, University of Southampton, who was not involved in the study.
“However, if the final results show an effectiveness of anywhere near 90 per cent with response in elderly and ethnic minority populations, that is an excellent result for a first generation vaccine.”
Downing Street welcomed the results as “promising” and said the UK will have procured 10 million doses by the end of the year to be given out if it is approved.
The UK has secured 40 million doses in total of the vaccine. However, people will need two doses of the jab, meaning not enough shots have been secured yet for the entire UK population.
The data from the full trial will be submitted for scientific peer-review publication.
How do scientists develop vaccines for new viruses?
Vaccines work by fooling our bodies into thinking that we’ve been infected by a virus. Our body mounts an immune response, and builds a memory of that virus which will enable us to fight it in the future.
Viruses and the immune system interact in complex ways, so there are many different approaches to developing an effective vaccine. The two most common types are inactivated vaccines (which use harmless viruses that have been ‘killed’, but which still activate the immune system), and attenuated vaccines (which use live viruses that have been modified so that they trigger an immune response without causing us harm).
A more recent development is recombinant vaccines, which involve genetically engineering a less harmful virus so that it includes a small part of the target virus. Our body launches an immune response to the carrier virus, but also to the target virus.
Over the past few years, this approach has been used to develop a vaccine (called rVSV-ZEBOV) against the Ebola virus. It consists of a vesicular stomatitis animal virus (which causes flu-like symptoms in humans), engineered to have an outer protein of the Zaire strain of Ebola.
Vaccines go through a huge amount of testing to check that they are safe and effective, whether there are any side effects, and what dosage levels are suitable. It usually takes years before a vaccine is commercially available.
Sometimes this is too long, and the new Ebola vaccine is being administered under ‘compassionate use’ terms: it has yet to complete all its formal testing and paperwork, but has been shown to be safe and effective. Something similar may be possible if one of the many groups around the world working on a vaccine for the new strain of coronavirus (SARS-CoV-2) is successful.
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