Video report from Science Editor Tom Clarke
The study looked at data from more than 23,000 healthcare workers aged 65 and under, from 104 England hospitals, who had received at least one dose of the Pfizer/BioNTech vaccine.
It found that those who receive a single dose of the jab had at least a 70% lower chance of becoming infected with coronavirus 21 days after vaccination, rising to 85% after a second dose.
Meanwhile, data collated from routine Covid testing on more than 12,000 people over-80 found at least 57% protection against coronavirus 28 days after vaccination with a single dose of Pfizer, rising to 88% after a second dose.
Among this age group, there was also thought to be at least 75% protection against severe disease.
Dr Mary Ramsay, head of immunisation at PHE, said this was at the “lower end of the estimate” and the drop in hospital admission and death was thought to be even more profound.
The PHE study also showed high levels of protection against the so-called UK variant.
The fresh data comes as a separate study from Scotland found the Pfizer and the Oxford/AstraZeneca vaccines were shown to reduce the risk of hospital admission from the virus by up to 85% and 94% respectively.Four weeks after receiving the initial dose, the Oxford jab appeared to reduce a person's risk of hospital admission by 94%, according researchers at the University of Edinburgh, the University of Strathclyde and Public Health Scotland.The study found that those who received the Pfizer jab had a reduction in risk of 85% between 28 and 34 days after the first dose.Data for the two jabs combined showed that among the over-80s - who are at high risk of severe disease - the reduction in risk of hospital admission was 81% four weeks after the first dose.
The researchers examined data between between December 8 and 15 February 15. During this period, 1.14 million vaccines were administered in Scotland - 21% of the Scottish population.
PHE is also monitoring the real-world impact of the AstraZeneca vaccine and will publish these findings in due course – but early signals in the data suggest it is providing good levels of protection from the first dose.
Commenting on the PHE study, Dr Ramsay said it provided "strong evidence" that the Pfizer-BioNTech vaccine is stopping people from getting infected, while also protecting cases against hospitalisation and death.
"We will see much more data over the coming weeks and months but we should be very encouraged by these initial findings.
“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.”
Dr Ramsay said: “This is strong evidence that the Pfizer/BioNTech vaccine is stopping people from getting infected, while also protecting cases against hospitalisation and death.
“We will see much more data over the coming weeks and months but we should be very encouraged by these initial findings.
“But protection is not complete, and we don’t yet know how much these vaccines will reduce the risk of you passing Covid-19 on to others.
“So even if you have been vaccinated, it is really important that you continue to act like you have the virus, practise good hand hygiene and stay at home.”
Health Secretary Matt Hancock said: “It is important that we see as much evidence as possible on the vaccine’s impact on protection and on transmission, and we will continue to publish evidence as we gather it.
“As we roll out the jab, it is vital people continue to play their role in protecting the NHS by sticking with the rules.”While no figure was given for how effective the Pfizer vaccine is at cutting transmission of the virus, researchers behind the healthcare study said it will cut transmission.
In that study, 84% of participants were female, 89% were white and 86% were in a role where they dealt directly with patients.
A quarter (26%) of participants had a reported medical condition, with asthma, obesity and diabetes the most common.