Data on infection in healthcare workers suggests that a single dose of Pfizer/BioNTech vaccine 'reduces the risk of catching infection by more than 70%' and that after two doses this rises to 85%.
Public Health England (PHE) said the findings provided 'strong evidence' that the vaccine could 'interrupt virus transmission' by stopping people from becoming infected - in addition to reducing risk of death or hospitalisation.
PHE added that early data suggested people who did become infected after receiving a single dose of vaccine were 'far less likely to die or be hospitalised'.
It said: 'Overall, hospitalisation and death from COVID-19 will be reduced by over 75% in those who have received a dose of the Pfizer-BioNTech vaccine.'
The findings come after early data from Scotland suggested that four weeks after administration of a first dose, risk of hospitalisation was reduced by up to 85% by the Pfizer/BioNTech vaccine and up to 94% by the Astra Zeneca vaccine.
Although the data published for England cover the Pfizer/BioNTech vaccine only, Mr Johnson told parliament that PHE had also found that the Oxford/Astra Zeneca vaccine provided a 'good level' of protection.
The prime minister said lockdown would be eased in four stages separated by five-week intervals, beginning with the reopening of schools on 8 March.
Seven days' notice will be given to confirm whether each further stage will proceed - and the timetable could be delayed if data suggests the pandemic is not easing as expected.
Decisions about further steps go ahead will be based on 'four tests' - around whether vaccine deployment is continuing as planned, vaccination is proving sufficiently effective, infection rates do not risk overwhelming the NHS and the emergence of new variants.
The prime minister hailed the impact of the UK vaccination programme, which he said had 'dramatically changed the odds in our favour'. 17.7m people UK-wide had received a first dose of COVID-19 vaccine by the end of 21 February - with around three quarters of jabs delivered by GP-led sites.
On the vaccination data, PHE head of immunisation Dr Mary 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 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.'
Health and social care 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.'
PHE also confirmed there is 'good evidence suggesting that giving the second dose of Oxford/AstraZeneca vaccine later will lead to much higher levels of protection' and that delivering the second dose 'at 12 weeks will therefore help to ensure longer lasting protection beyond the current restrictions'.
The four-stage plan to ease lockdown will begin with schools reopening on 8 March, with non-essential retail to return on 12 April, 'most restrictions on outdoor meetings' to lift from 17 May and 'all limits on social contact' potentially dropped from 21 June. People will be allowed to meet one other person outdoors from 8 March and the rule of six allowing increased contact between two households will return outdoors from later in March.