PHE said results from its Siren (Sarscov2 Immunity and reinfection evaluation) study, looking at infections among 40,000 NHS workers who were being tested for Covid every two weeks, found the vaccine successfully prevented both symptomatic and asymptomatic infections, reducing cases by more than 72 per cent 21 days after a first dose.
This increased to 86 per after a second dose.
Two new studies have examined the real-world effectiveness of the Pfizer jab as Boris Johnson unveiled his roadmap for releasing lockdown in England on Monday. Schools will fully reopen on 8 March and families will be able to meet outdoors from the end of March.
A separate analysis of routine Covid testing data also revealed one dose of the vaccine was 57 per cent effective against symptomatic infections in those aged over 80, four weeks after the first dose.
A second dose increases protection in those over 80 to more than 85 per cent. Overall, hospitalisation and death from Covid-19 could be reduced by 75 per cent, PHE said.
The analysis shows the vaccine is effective against the southeast variant of the virus which triggered a surge in cases across England in the autumn.
Research in Scotland, also released on Monday, showed both the Pfzer and Oxford/AstraZeneca vaccine cut hospitalisations by up to 85 and 94 per cent respectively.
In a briefing for journalists, Dr Susan Hopkins, from PHE, said: “We’re seeing a really strong effect to reducing any infection, asymptomatic and symptomatic. This is the first time this has been done in a systematic way for the Pfizer/BioNtech vaccine.”
She added that the results potentially meant the vaccine was successful in stopping transmission of the virus: “Reducing people with infection, both symptomatic and asymptomatic, is the biggest thing that will reduce transmission, and we’re showing that not only are you reducing symptomatic infection, you’re reducing the numbers of those with asymptomatic infection as well.”
The second study compared vaccinated patients with similar patients based on age, sex, region and whether they lived in a care home between 8 December and 12 February.
In total there were 43,294 cases in those aged over 70 and 11,860 infections among those aged over 80.
The risk of dying in those aged over 80 was 57 per cent less than those who were unvaccinated at least 14 days after receiving the first dose.
Those over 80 who develop Covid-19 infection after vaccination were around 40 per cent less likely to be admitted to hospital than someone who had not been vaccinated.
Dr Mary Ramsay, head of immunisation at PHE, said: “Not only is the vaccine reducing the risk of someone becoming a case, it’s then reducing further on top of that, the risk of them needing to be hospitalised or dying unfortunately.
“So this really shows us that the protection against the most severe forms of disease is even higher. That 57 per cent [risk of death] is very much a low estimate, the protection against severe disease is probably at least 75 per cent, if not higher.
“I think that does reinforce the policy of giving that single dose to more people to prevent more deaths and more admissions now, and then go back later and get the second dose which will give them longer lasting protection, and potentially give better protection, particularly against those milder forms of disease.”
She added: “But protection is not complete, and we don’t yet know how much these vaccines will reduce the risk of you passing Covid-19 onto others. So even if you have been vaccinated, it is really important that you continue to act like you have the virus, practice good hand hygiene and stay at home.”
PHE said it was carrying out similar analyses for the Oxford/AstraZeneca vaccine which started to be used in the UK at the beginning of January.
Health secretary Matt Hancock said: “This crucial report shows vaccines are working – it is extremely encouraging to see evidence that the Pfizer vaccine offers a high degree of protection against coronavirus.
“Vaccines save lives, and so it is vital we roll out the vaccine programme as fast as possible, and that as many people as possible take the jab. This new evidence shows that the jab protects you, and protects those around you.”