Coronavirus infections in England halved in recent months, according to a study, but concerns remain about the threat from new variants.

Prevalence of infections dropped by 50% between March and early May, and is at its lowest since August, new data suggests.

But the figures come amid a warning from Boris Johnson that new variants “pose a potentially lethal danger”.

The Prime Minister said there is “increasing concern” in the UK about the variant first identified in India.

However, the European Medicines Agency said on Wednesday it was “pretty confident” that vaccines currently in use are effective against the Indian variant – a view echoed by some British scientists.

Professor Paul Elliott, director of Imperial College London’s React programme, cited the Indian variant when asked whether the study’s latest data supported a move into the next stage of easing lockdown restrictions.

He said: “It is a difficult question because we have low levels of prevalence in the community, and we’ve got low levels of disease in hospitals and deaths, so that’s good.

“But I think that the patterns in the Indian variant are cause for some concern.”

He added that further studies are needed to really understand the characteristics and the spread of the Indian variant which appears to be at least as transmissible as the Kent variant.

The React study looked at variants of coronavirus and found that of 115 positive swabs, 24 cases were identified as the Kent variant, and two of three cases in London were identified as the Indian variant of concern.

The experts said neither participant had been abroad in the previous two weeks.

The Scientific Advisory Group for Emergencies (Sage) is reportedly due to hold an emergency meeting on Thursday to discuss the spread of the Indian variant amid fears it could impact the Government’s road map out of lockdown.

Overall, between the last round of the React study which looked at data from March, and the current round which looked at data from April to the beginning of May, swab-positivity dropped by 50% in England from 0.20% to 0.10%.

Experts estimate the corresponding R number to be 0.90.

The data includes 127,408 swab tests carried out across England between April 15 and May 3.

Researchers found there was a fall in all age groups except the 25 to 34-year-olds, with a “significant” fall in the 55 to 64-year-olds.

Prof Elliott, director of the React programme, told a press briefing: “This coincides with the rollout of the vaccine programme to the younger part of that age group.”

The data also suggests higher prevalence among participants of the Asian community.

Researchers said the divergence between the pattern of infections and a pattern of hospital admissions and deaths suggests the rollout of mass vaccination is preventing severe outcomes.

Steven Riley, professor of infectious disease dynamics at Imperial College London, said: “What you can see in recent times – basically since the widespread rollout of the vaccine – and we showed this last time, that you see a decoupling of the relationship between the React infection and a lagged number of deaths.

“And this gap is showing how we can have more infections in the population with far fewer deaths.

“And we actually see that difference growing nicely now for hospitalisations as well, so for each infection in the community we are producing fewer hospitalisations and far fewer deaths.”

Health Secretary Matt Hancock said the findings “demonstrate the impact our incredible vaccination rollout is having on Covid-19 infection rates across the country, with prevalence lowest amongst those more vulnerable people aged 65 and over”.

Meanwhile families bereaved in the pandemic welcomed Mr Johnson’s announcement that there will be an independent public inquiry into the handling of the crisis, but said the start date of spring next year is “simply too late”.

Jo Goodman, co-founder of the Bereaved Families for Justice group, who lost her father Stuart to Covid, said: “It sounds like common sense when the Prime Minister says that an inquiry can wait until the pandemic is over, but lives are at stake with health experts and scientists warning of a third wave later this year.”

Number 10 has defended the timescale, stating that “these sorts of inquiries do require a great deal of Government time with officials who are currently working on our Covid response”.