Prior covid infection reduces new risk for 10 months, antibodies study finds

The risk of being infected with Covid is substantially reduced for at least 10 months after a first infection, a study has found.

University College London (UCL) researchers studied 682 care home residents and 1,429 staff in 100 care homes in England to find out how many people who contracted Covid in the first wave also tested positive in the second wave. 

The study found that care home residents with a previous infection were 85 per cent less likely to be infected between October last year and February this year than residents who had never been infected.

Meanwhile, staff with past infection were 60 per cent less likely to be infected than staff who had not had the infection before. Most of the reinfection cases suffered symptoms, but none required hospitalisation. 

The findings indicated that antibodies from a prior infection can protect against Covid for at least 10 months and that the risk of re-infection is less than one per cent a month. 

The researchers said the results showed strong protection in both groups but that the two percentages may not be directly comparable as staff may have accessed testing outside the care home, leading to positive tests not being included in the study. 

They also cautioned that residents who tested positive for antibodies likely represented a particularly robust group, having survived the first wave of the pandemic.

Although more research is required, the findings are the latest evidence to suggest that natural immunity to the virus is long-lasting. This is particularly good news for the UK, which has recorded the seventh-highest number of cases in the world at almost 4.5 million.

The study’s lead researcher, Maria Krutikov of the UCL Institute of Health Informatics, said: “It’s really good news that natural infection protects against reinfection in this time period. The risk of being infected twice appears to be very low.” 

She said: “The fact that prior Covid-19 infection gives a high level of protection to care home residents is also reassuring, given past concerns that these individuals might have less robust immune responses associated with increasing age. These findings are particularly important as this vulnerable group has not been the focus of much research.”

The researchers said the study period covered the emergence of the more contagious variant first identified in the UK and now known as Alpha, implying a good level of protection against that variant. 

The concerning variant initially discovered in India and now designated the Delta variant has subsequently emerged and become dominant in Britain.