There was a flurry of good news stories today about the UK’s efforts to vaccinate the population against Covid-19.

At time of writing, more than 18 million people have been jabbed across Britain. More than 93 per cent of over-80s in England have received a first dose of one of the two available vaccines.

The number of coronavirus cases has been falling for a while now across the UK, along with the number of people in hospital and deaths linked to the disease.

But how can we be sure that the vaccines are responsible for this positive trend? How do we know the fall in cases, serious illness and death is not due to lockdown measures?

Scientists are now tentatively beginning to conclude that we can see the effect of the vaccines in the figures. Here’s why.

Scottish study

This pre-print (not peer-reviewed) paper from the University of Edinburgh analysed data from 5.4 million people – almost the entire population of Scotland.

When the researchers compared the health outcomes of the 1.1 million people who had been vaccinated by 15 February with those not yet vaccinated, adjusting for differences in age, sex, socioeconomic status and underlying health conditions in the two groups.

They found that a single dose of Pfizer vaccine was enough to reduce the risk of being hospitalized by 85 per cent, four weeks after the jab. The AstraZeneca vaccine cut the risk by 94 per cent.

The combined results for both vaccines showed an 81 per cent reduction in hospitalisation risk for people aged 80 and over at four weeks after vaccination.

Public Health England data

We also have results from Public Health England’s SIREN study today, which looks at whether there were fewer cases of infection – with or without symptoms – among NHS workers who were given the Pfizer vaccine.

The Kent variant of the virus was found to be the dominant one in this group of people.

The risk of being infected was reduced by 70 per cent three weeks after the first dose and by 85 per cent a week after the second.

Other data released by Public Health England found that a single dose of Pfizer vaccine was 57 per cent effective against symptomatic Covid in the over-80s from four weeks, rising to 88 per cent a week after the second dose.

Vaccination also significantly cut the risk of going to hospital or dying among people over 80, Public Health England said.

Deaths and hospital cases falling faster amongst highly-vaccinated group

PHE figures show that both hospitalisation and death rates have been falling more quickly recently among the oldest age group (the blue line here) than in younger cohorts (orange and grey). This didn’t happen after the first wave of the pandemic last year.

Since the over-80s are more likely to have been vaccinated than anyone else, this could be a sign that the vaccines are already reducing serious illness and mortality, although Public Health England are cautious about saying how big the vaccine effect is compared to the impact of lockdown measures.

International evidence

Some of the results released today echo the experience of Israel, the country with the highest vaccination rate in the world.

Studies from Israel have also shown that a single dose of Pfizer vaccine cut cases of symptomatic infection significantly in healthcare workers.

Limitations of vaccines

The authors of the Siren study say there is now “strong evidence that vaccinating working-age adults will substantially reduce asymptomatic and symptomatic SARS-CoV-2 infection and therefore reduce transmission of infection in the population”.

But they add: “It does not eliminate infection risk completely and therefore personal protective equipment, non-pharmaceutical interventions and regular asymptomatic testing will need to be continued until prevalence of SARS-CoV-2 is extremely low to reduce the risk of transmission in healthcare settings.”

Government scientists have echoed this today, saying that even with high levels of individual protection, and large numbers of people taking up the offer of a jab, the whole population will not be immune to Covid and there is still the risk of an upsurge in cases.

The Chief Scientific Adviser, Sir Patrick Vallance, said: “Vaccines are predicted, as you would expect and hope, to make a big difference.

“But even with high vaccine levels, and indeed quite high vaccine coverage, it’s important to remember that a large number of people in the population remain unprotected.”

The verdict

New research released today suggests the UK experience may be mirroring the good results already seen in Israel following the mass vaccination there.

A huge study covering almost the entire population of Scotland shows that both the Pfizer and AstraZeneca vaccines appear to drastically cut the risk of ending up in hospital with Covid.

There are a lot of positives that can be drawn from the evidence from Scotland and England so far: both the vaccines that are licensed and widely available in the UK appear to work; the AstraZeneca vaccine appears to work well in older people, despite European leaders expressing concerns over the lack of evidence; the Pfizer vaccine has been shown to be effective against the “Kent variant” of the disease; and the UK’s controversial policy of giving large numbers of people one dose and making people wait for up to 12 weeks to get the second appears to be paying off.

Some scientists are cautious about the data so far, saying that it’s hard to disentangle the effect of the vaccines from other measures the government has taken to curb the spread of the virus.

And the government’s scientific advisers are insisting that the country still needs to come out of lockdown slowly, despite the promising early data on vaccines.