Antibodies can protect against Covid for at least 10 months

People who have previously caught Covid-19 are protected from reinfection for at least ten months, a study has found. 

The findings, published in the Lancet, is reassuring for many of Britain’s almost 4.5million cases, and builds on previous studies which indicate natural immunity to the virus is long-lasting. 

Researchers looked at how many people who contracted Covid-19 in the first wave also tested positive in the second wave. 

UCL researchers studied 682 care home residents and 1,429 staff in 100 care homes in England.

A third of the elderly residents who took part in the study — with an average age of 85 — tested positive for antibodies in summer last year, evidence they had been infected during the spring of 2020.

Of the 634 people in the study who had antibodies (408 staff and 226 residents) in summer 2020, only four residents and ten staff then tested positive between October 2020 and February 2021, a period of time which encompassed the peak of the second wave and the emergence of the more transmissible Kent variant which ran rampant and led to the cancellation of Christmas. 

Most of the reinfection cases suffered symptoms, but none required hospitalisation. 

This compares to 93 resident and 111 staff infections during the second wave among the 1,477 study participants who did not have antibodies. 

Read more: I've had Covid and a jab. Why was my antibody test so low?

Writing in the study, the researchers say residents who have already had the virus are 85 per cent less at risk of infection than someone who never had Covid. 

Staff were found to be 61 per cent less at risk than previously uninfected colleagues. 

“These findings are broadly consistent with findings from large cohort studies of hospital staff, and extend the evidence of substantial protection to frail older people, who are susceptible to severe outcomes of SARS-CoV-2 infection due to age-related changes in immunity and high levels of comorbidity,” the researchers write in the paper. 

As part of the study, called Vivaldi 2, antibody tests were dished out to all participants in the study in June and July of 2020 to determine how many people had previously been infected. 

Staff from that point on were given a PCR test every week, and residents a swab once a month. 

Anyone who received a vaccine was taken out of the study 12 days after their first dose to ensure the statistics were solely for natural immunity, and not skewed by protection from a jab. 

The researchers say this indicates prior infection with Covid-19 confers long-term protection lasting at least ten months, and the risk of re-infection is less than one per cent a month. 

Dr Laura Shallcross, senior author of the paper from the UCL Institute of Health Informatics, said: “This was a unique opportunity to look at the protective effect of natural infection in this cohort ahead of the roll-out of vaccination.

“An important next step is to investigate the duration of immunity following natural infection and vaccination and to assess whether this protective effect is maintained against current and emerging variants.”

Professor Ian Jones, professor of virology, University of Reading, who was not involved in the research, said: “There were concerns early in the pandemic that protection would be short lived but this data suggests otherwise and it is particularly encouraging that this applied as much to those over 65 as those under. 

“If the same is true of vaccinated individuals, which seems likely, boosters may not be needed as frequently as has been supposed. 

“The few people that did become reinfected all had low virus levels suggesting that virus circulation will remain suppressed in immune populations which in turn will limit the occurrence of variants.”