According to the research, published in the European Journal of Immunology, the participants had antibodies with confirmed neutralisation activity for up to six months post infection with the SARS-CoV-2 virus.
The scientists, led by Marc Veldhoen from Instituto de Medicina Molecular (IMM) in Portugal, monitored the antibody levels of over 300 COVID-19 hospital patients and healthcare workers, 2500 university staff, and 198 post-COVID volunteers.
They setup an in-house sensitive specific and versatile COVID-19 serology test.
The study revealed that 90 per cent of subjects have detectable antibodies up to seven months post contracting COVID-19.
It also found that age was not a confounding factor in levels of antibodies produced, but disease severity is.
“Our immune system recognises the virus SARS-CoV-2 as harmful and produces antibodies in response to it, which helps to fight the virus,” Voldhoen said.
“The results of this six months cross-sectional study show a classic pattern with a rapid increase of antibody levels within the first three weeks after COVID-19 symptoms and, as expected, a reduction to intermediate levels thereafter,” he added.
Based on the findings, the scientists said men produce more antibodies on average than women, “but levels equilibrate during the resolution phase and are similar between the sexes in the months after SARS-CoV-2 infection”.
In the acute phase of the immune response, the researchers observed higher antibody levels in subjects with more severe disease.
They said age is not a confounding factor for the production of antibodies since no significant differences were observed between age groups.
While there was a reduction in the levels of antibodies over time, the team found that there was “robust neutralisation activity” for up to the seventh month post-infection in a large proportion of previously virus-positive screened subjects.
“Our work provides detailed information for the assays used, facilitating further and longitudinal analysis of protective immunity to SARS-CoV-2,” Veldhoen said.
“Importantly, it highlights a continued level of circulating neutralising antibodies in most people with confirmed SARS-CoV-2,” he added.
The researchers believe the next months will be critical to evaluate the robustness of the immune response to SARS-CoV-2 infection, and to find clues for questions such as the duration of circulating antibodies and the impact of reinfection.