The crucial R number is now around 1 in England as the fall in new Covid cases “flattens off”, major research has found.
New coronavirus infections have now “plateaued” at around one in every 500 people and are no longer falling, the REACT study said.
Prevalence of cases dropped by 60% between February and March – but they are still higher than they were in summer 2020.
Imperial College London’s REACT study is the largest of its kind in England, testing 140,000 volunteers between March 11-30.
It found that, while cases did not rise after schools reopened on March 8, the rapid decline in cases “appears to have stopped”.
The study added: “Future rounds of REACT-1 will be able to measure the rate of growth or decline from this current plateau.
“And hence help assess the effectiveness of the vaccination roll-out on transmission of the virus, as well as the potential size of any third wave during the ensuing months.”
The study estimated R is around 1 in England – which means each person with Covid-19 infects one other person on average before recovering or dying.
If the R number rises above 1, as scientists believe it may do when beer gardens open next Monday, the number of cases will rise.
If enough people are vaccinated it could be enough to keep large rises in cases at bay. But SAGE earlier this week warned of a third wave as soon as late July, with projections suggesting more than 15,000 extra people could die by June 2022.
Experts found that the rate of infection fell in all age groups and regions across those two months, with figures also indicating that the vaccine rollout could be “breaking the link” between infections, deaths and hospital admissions.
Researchers found there have been “big falls” in prevalence of the virus in the South East and London from February to March.
But there remain “persistent areas of higher prevalence” of the virus in the southern part of Yorkshire, and parts of the East Midlands and the North West.
The 10th round of tests was conducted between March 11 and March 30, with 140,844 swabs collected, returning 227 positive results.
This is compared with 689 positive results out of 165,456 swabs from February 4 to February 23.
The researchers’ findings, due to be released as a pre-print, were outlined in a briefing to journalists on Wednesday.
- The rate of infection in the community was 0.20% in March – down from 0.49% in February and 1.57% in January.
- While on average there had been an overall decline in Covid prevalence over the whole of February and March, researchers observed last month’s data indicated this had flattened off.
- Using March data alone, the reproduction number (R) – the average number of people an infected person is likely to pass the disease on to – was estimated to be 1.
- Covid-19 prevalence decreased across all age groups between February and March, with the highest prevalence now among five to 12-year-olds and lowest in those aged 65 and above.
- In February and March, the number of foreign journeys compared with earlier months was “very, very low” on average.
- Comparing infections and death and hospital admissions, researchers observed “fewer deaths per infection” than they would have expected based on recent prior months of the study.
Steven Riley, professor of infectious disease dynamics at Imperial College London, said: “The good news is prevalence has decreased by approximately 60% from the previous round in February to the current results now in March.
“The most recent data doesn’t show a continued obvious decline, we have a levelling off of prevalence, and that’s reflected in an R estimate of 1.
“And we see some divergence between our observed patterns of infection and patterns of death since January, which we think probably suggests that the mass vaccination is breaking that link to some degree between infections and deaths.”
Commenting on infection, deaths and hospital admissions data, he said: “We’re observing fewer deaths per infection than we would have expected based on the recent prior months of the study.”
He added: “To a lesser extent, we’re seeing fewer hospitalisations per infection as well.
“We think that this is a signal of how the vaccination programme is breaking the link, the previously strong link, between the pattern of infections and the patterns of deaths and hospitalisations.”