Antibodies produced following natural infection of Covid-19, and potentially following vaccination, may protect most people against subsequent infection for at least six months.

The study by UK Biobank, the UK’s major biomedical database and research resource - found that 99% of participants who had tested positive for previous infection retained antibodies to Covid-19 for three months after being infected, and 88% did so for the full six months of the study. 

For the 6-month period from the end of May 2020 to the beginning of December 2020, UK Biobank collected monthly blood samples and data on potential symptoms from 20,200 UK Biobank participants and their adult children and grandchildren. 

It found that the proportion of the population with antibodies to Covid-19 rose from 6.6% at the start of the study period (May/June 2020) to 8.8% by the end of it (November/December 2020).

Detectable Covid-19 antibodies lowest in older patients

There was no difference in seroprevalence (past infection) by gender, but the proportion of participants with detectable antibodies was higher in younger people (13.5% among those under 30) and lowest in the older people (6.7% among those over 70).

The seroprevalence of Covid-19 was highest among participants of Black ethnicity (16.3%) and lowest among those of White (8.5%) and Chinese ethnicities (7.5%).

The most common symptom associated with having antibodies to Covid-19 was a loss of sense of taste and smell, which was reported by 43% of sero-positive participants. About one-quarter (24%) of sero-positive participants were completely asymptomatic and 40% did not have one of the three ‘classic’ Covid-19 symptoms (fever, persistent dry cough or loss of sense of taste or smell).

The data will be added to the UK Biobank database and research resource, enabling scientists globally to conduct further research into how Covid-19 infection affects health over the longer-term.

Professor Naomi Allen, UK Biobank Chief Scientist, said: "We are incredibly grateful to all the UK Biobank participants, and their children and grandchildren, who provided us with their blood samples for six months. This important study has revealed that the vast majority of people retain detectable antibodies for at least 6 months after infection with the coronavirus.

"Although we cannot be certain how this relates to immunity, the results suggest that people may be protected against subsequent infection for at least 6 months following natural infection and, potentially, vaccination. More prolonged follow-up will allow us to determine how long such protection is likely to last."