One vaccine dose gives high protection from severe Covid, evidence shows

Real-world evidence from the Covid vaccination programmes in England and Scotland show that one dose of vaccine gives high protection against severe disease and admission to hospital – and protects against even mild disease with no symptoms in younger people.

The first real data from the mass vaccination programmes is promising, and although the results do not include evidence that they prevent transmission completely, there is data to show they are stopping some people becoming infected, which should slow the spread of coronavirus.

Three studies came to similarly positive conclusions about the protection offered by the vaccines – one in Scotland and two in England – although they were set up to look at the effects in different groups of people.

In England, the Siren study in healthcare workers under 65 found that one dose of the Pfizer/BioNTech vaccine reduced the risk of catching the virus by 70% – and 85% after the second dose. The healthcare workers were all tested for the virus every two weeks, so the study picked up asymptomatic infections as well as those who had symptoms.

Public Health England also released the results of routine testing in the over-80s, who are at higher risk of becoming severely ill and dying from Covid. That found that 3 weeks after the first dose, the Pfizer/BioNTech vaccine was 57% effective against symptomatic illness, whether mild or more severe. Although not many people have had a second dose, the evidence suggested efficacy rose to 85% in those who did.

The data also shows that people who have been vaccinated who catch the infection are much better protected against severe disease, hospitalisation and death.

“On top of the reduction in symptomatic infection, vaccine protection against more severe disease from a single dose is even higher – at least 75%,” said Mary Ramsay, head of immunisation at PHE, at a briefing.

She said these results justified the government’s policy of giving a first dose to millions of people and delaying the second dose for up to 12 weeks later.

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Ramsay said: “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 them better protection.”

Matt Hancock said the results were evidence that the strategy was successful. The health secretary 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.”

The data from Scotland was equally encouraging. While the studies in England looked only at people given the Pfizer/BioNTech vaccine, which was available from the first week in December, Scottish experts analysed data from both vaccines over a period of 28 days.

By the fourth week after receiving the initial dose, the Pfizer and Oxford/AstraZeneca vaccines had reduced the risk of hospital admissions from Covid-19 by up to 85% and 94% respectively, according to a study by Scottish universities and Public Health Scotland.

Among people aged 80 and over, vaccination was associated with an 81% reduction in hospital admission risk in the fourth week, when the results for both vaccines were combined.

The scientists, whose work is available online but has not yet been peer-reviewed, said the results from the two vaccines should not be compared. There was more data on people who were given the Pfizer vaccine, while the AstraZeneca vaccine had mostly been administered to older people.