Medical Health Cluster

15 marzo, 2022

‘Uptick’ in COVID Cases Among Older People in February Could Stem from Waning Immunity

Cases of COVID-19 show signs of rising among the over-55s, raising the possibility that the pandemic could be prolonged by the spread of the BA.2 sub-lineage of the Omicron variant, a study has suggested. Increased socialising and waning immunity after vaccination could be behind the development, scientists led by a team from Imperial College London (ICL) said.

The latest analysis from the Real-time Assessment of Community Transmission-1 (REACT-1) study, presented in a preprint paper, estimated weighted mean prevalence of the virus in England as 2.88% (95% CI 2.76 to 3.00) between February 8 and March 1 – down from 4.41% in January.

Although lower than the January peak – fuelled by emergence of the rapidly transmissible Omicron variant – prevalence of SARS-CoV-2 remained high in England during February, early data suggested.

However, prevalence remains higher than the 1.57% seen around the same time last year just after the peak of the second COVID wave caused by the Alpha variant. They estimated that the R number for the latest study round was 0.94 (95% CI 0.91 to 0.96).

‘Beginning of an Uptick’

Infection levels fell among older school-age children and adults aged 18 to 54, but had plateaued or increased among those aged 55 and over, the scientists found.

“At the moment, we’re possibly seeing the beginning of an uptick, but we don’t know where it’s going to go right now,” said ICL’s Prof Paul Elliott, the REACT programme director.

Samples were taken at random from 94,950 people with valid nose and throat swab results by PCR testing.

Among 1195 positive samples, only one was identified as the Delta variant, and the remainder (99.9%) were Omicron.


The proportion of Omicron sub-lineages from the samples indicated that 32.7% were BA.1, 39.6% BA.1.1, and 27.7% were BA.2. The extra R number advantage of BA.2 was estimated at 0.40 versus BA.1 or BA.1.1.

The highest proportion of BA.2 among positive samples was found in London.

R Number Above 1 in Older Age Groups

Prevalence of SARS-CoV-2 decreased in all age groups between round 17 and 18. The highest proportion of positive samples was found among children aged 5 to 11 (4.69%), and the lowest in the over-75s (1.68%).

The R number was estimated at 1.04 for people aged 55 and older, 0.79 at ages 5 to 17, and 0.92 for those aged 18 to 54.

At a briefing hosted by the Science Media Centre, Prof Elliott explained: “There’s probably been more mixing of the population recently, and possibly more mixing between age groups, so that the older people maybe are becoming more exposed.

“But also, we do think that the waning of the vaccine booster may be playing a part, because many of that group had their booster last year, maybe September, October, November.”


Ongoing surveillance of hospital data was needed to track outcomes for older people, the scientists urged.

Dr Simon Clarke, associate professor in cellular microbiology at the University of Reading, commented: “Whether the UK sees the number of hospitalisations like we have seen previously, and whether admissions result in a higher proportion of patients going to ICU, remains to be seen, and it’s the latter that will be important as it’s something of a bottleneck for the NHS.

“It shouldn’t be forgotten that our ability to treat serious infections is now much better than at any time and will continue to improve, but none of these are 100% successful.”

Clinical virologist Dr Julian Tang from the University of Leicester said that “as the Omicron variant adapts further to this well-vaccinated human population, we may see more vaccine-escape capable variants arising, with higher viral loads and increased transmissibility”.

He added: “Living with COVID-19, as with seasonal flu, will be in the context of the emergence of new variants with different properties – not all of which will be well-controlled by vaccines – leading to fluctuating levels of infections/reinfections – and inevitably a varying number of hospitalisations and deaths.”

Créditos: Comité científico Covid

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