London, Aug 9 (IANS): Pre-existing antibodies against human cold coronaviruses (HCoV) can likely confer cross-protection against Covid-19 infection, suggests a study.
The study, led by researchers at the Barcelona Institute for Global Health (ISGlobal), found that people who were infected by SARS-CoV-2, the virus causing Covid-19, had lower levels of HCoV antibodies.
Moreover, asymptomatic individuals had higher levels of anti-HCoV IgG and IgA than those with symptomatic infections.
The study, published in Nature Communications, also showed that the levels of IgG antibodies against the spike protein of SARS-CoV-2 remain stable, or even increase, seven months after infection.
"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," ISGlobal researcher Carlota Dobano said.
For the study, the team analysed blood samples from 578 participants, taken at four different timepoints between March and October 2020.
They used the Luminex technology to measure, in the same sample, the level and type of IgA, IgM or IgG antibodies to six SARS-CoV-2 antigens as well as the presence of antibodies against the four coronaviruses that cause common colds in humans. They also analysed the neutralising activity of antibodies.
The results 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.
With the exception of IgM and IgG antibodies against the nucleocapsid (N), the rest of IgG antibodies (including those with neutralising activity) remained stable over time, confirming results from other recent studies.
"Rather surprisingly, we even saw an increase of IgG anti-Spike antibodies in 75 per cent of the participants from month five onwards, without any evidence of re-exposure to the virus," the study's senior co-author Gemma Moncunill said. No reinfections were observed in the cohort.