Mild cases may bestow far lower immunity, says study

People who catch Covid-19 but don’t show symptoms may have significantly lower levels of immunity against the virus than those who become severely ill, new research showed.

The majority of virus patients display relatively minor signs of infection, and a small proportion show no symptoms at all.

Very little is known about this group, given that they are far less likely to be tested than those who go on to develop severe symptoms including respiratory problems.

Researchers based in China compared two groups of individuals infected with Covid-19 in Chongqing’s Wanzhou district: 37 who showed symptoms versus 37 who did not.

The researchers analysed blood samples from both groups taken a few weeks after recovering and found that just 62.2% of the asymptomatic group had short-term antibodies, compared with 78.4% of symptomatic patients.

After eight weeks of convalescence, antibody presence had fallen in 81.1% of asymptomatic patients, compared with 62.2% of symptomatic patients.

What’s more, asymptomatic patients were found to have lower levels of 18 pro- anti-inflammatory cell-signalling proteins than the symptomatic group, suggesting a weaker immune response to the novel coronavirus.

Authors of the study, which was published in Nature Medicine, said their findings called into question the idea that everyone who has had coronavirus are immune to future infection.

“This data might indicate the risks of using Covid-19 ‘immunity passports’ and support the prolongation of public health interventions, including social distancing, hygiene, isolation of high-risk groups and widespread testing,” they wrote on Thursday.