COVID Infections in Care Home Residents Over Double that in General Population

Dr Rob Hicks

January 24, 2022

Research published in The Lancet Healthy Longevity  has found that in England more than 1 in 3 care home residents, and more than 1 in 4 care home staff, were infected with SARS-CoV-2 during the first two waves of the pandemic.

The researchers from University College London cautioned that since nucleocapsid-specific antibodies – which indicate prior SARS-CoV-2 infection - often become undetectable within the first year following infection, there is likely to be a "marked underestimation of the true proportion of people with previous infection".

Figures May Be Underestimated

For their study the researchers looked at 9,488 blood samples from nearly 5000 residents (1434) and staff (3288) at 201 care homes across England between June 2020 and May 2021. Average age of residents was 87 years, and that of staff was 48 years. Individuals donated a maximum of four samples, taken at least 8 weeks apart.

The researchers found that 34.6% of residents and 26.1% of staff tested positive for  the nucleocapsid antibody. These figures compared with 16.6% of the general population testing positive from June 14 to July 11, 2021, according to national surveillance data. The researchers said that the data "did not include residents and staff who died of COVID-19, meaning the true prevalence would have been higher".

Lead author Dr Maria Krutikov (UCL Institute of Health Informatics) said: "Our study shows the prevalence of COVID-19 in care homes was much higher than in the general population in England up until May this year. In the period we looked at, before the Delta variant became dominant in the UK, the proportion of care home residents with evidence of previous infection with SARS-CoV-2 was more than double that of the general population."

Test No Longer Picks Up Prior Infection

After analysing repeat samples from 619 participants, and how these changed over time, the researchers estimated that for half of the population it would take 8 months for the nucleocapsid antibody to become undetectable, highlighting that "antibody titres against nucleocapsid protein wane significantly over the first 8 months following infection", meaning, they said, that "in half of the population the test no longer picked up evidence of prior infection".

Senior author Professor Laura Shallcross from UCL Institute of Health Informatics, leader of the Vivaldi study looking at COVID-19 in care homes, said: "In our study the nucleocapsid-specific antibody disappears within a year and the wide use of tests targeting these antibodies to see if people have had Covid-19 before could underestimate the number of prior infections."

Novel Tests Need Developing

Prof Shallcross, added: "It is important to distinguish immunity caused by infection from immunity generated by a vaccine within a population. Underestimating the number of past infections could affect our estimates of the effectiveness of a vaccine and the level of protection against infection in care homes, as both of these are boosted by naturally-acquired immunity."

The authors concluded by pointing out that since the nucleocapsid antibody assay used is the "current gold standard for assessment of previous natural infection", it is likely that many people with past natural infection will be "falsely labelled as infection-naïve", with resultant underestimation of past infection in this population.

They emphasised that previous natural infection status is an important determinant of both the vaccine response and risk of reinfection and, as such, "novel serological assays to determine previous infection status should be developed".

The research is part of the ongoing Vivaldi study, launched in June 2020, to investigate SARS-CoV-2 infections in care homes and inform strategies to protect residents. It is funded by the UK Department of Health and Social Care.

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