Covid antibodies remain stable - or even increase - seven months after infection, according to the biggest study of its kind.
Researchers also found that pre-existing antibodies to common cold coronaviruses may be protective against Covid-19.
The follow-up study among a group of healthcare workers was coordinated by the Barcelona Institute for Global Health (ISGlobal) in Spain.
Scientists say it is crucial to better understand the dynamics and duration of immunity to SARS-CoV-2 - the virus that causes Covid-19 - to predict the pandemic’s evolution and develop effective strategies to combat its spread.
With that goal in mind, a team led by ISGlobal researcher Professor Carlota Dobaño followed a group of healthcare workers from the beginning of the pandemic to evaluate the levels of antibodies against different SARS-CoV-2 antigens over time.
Prof Dobaño. said: "This is the first study that evaluates antibodies to such a large panel of SARS-CoV-2 antibodies over seven months."
The researchers analysed blood samples from 578 participants, taken at four different times between March and October last year.
They measured the level and type of antibodies to six different SARS-CoV-2 antigens as well as the presence of antibodies against the four coronaviruses that cause common colds in humans.
The results, published in the journal Nature Communications, show that the majority of infections among healthcare workers occurred during the first pandemic wave.
The percentage of participants with SARS-CoV-2 antibodies increased only slightly between March and October – from 13.5 per cent to 16.4 per cent.
Antibodies largely remained stable over time, confirming results from other recent studies. No reinfections were observed in the group.
Study senior co-author Assistant Research Professor Gemma Moncunill said: “Rather surprisingly, we even saw an increase of anti-Spike antibodies in 75 per cent of the participants from month five onwards, without any evidence of re-exposure to the virus."
Regarding antibodies against human cold coronaviruses (HCoV), the results suggest that they could confer cross-protection against Covid-19 infection or disease.
People who were infected by SARS-CoV-2 had lower levels of HCoV antibodies. Asymptomatic individuals had higher levels of anti-HCoV antibodies than those with symptomatic infections.
Prof Dobaño added: “Although cross-protection by pre-existing immunity to common cold coronaviruses remains to be confirmed, this could help explain the big differences in susceptibility to the disease within the population."
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