IgA antibodies seem to protect unvaccinated against COVID-19
Despite daily contact with Covid-19 patients early in the pandemic, some health professionals avoided falling ill. As a University of Gothenburg study shows, the explanation appears to be an antidote in the immune system: IgA antibodies to COVID-19.
To understand how the immune system builds up its defences against COVID-19, a group of researchers at the University’s Sahlgrenska Academy monitored 156 employees at five primary care health centres belonging to the Nötkärnan group in the Gothenburg area for six months.
None of the recruits, recruited during April and May 2020, had been vaccinated against COVID-19, and most saw infected patients daily.
Some of the staff did not contract the disease, which seems to have been due to IgA (immunoglobulin A) being present in their respiratory tract. These antibodies, found naturally in the secretions of mucous membranes in the airways and gastrointestinal tract, can protect the body by binding to viruses and other invading organisms.
One in ten protected
The study's results, published in the European Journal of Immunology, show that a third of the care workers developed antibodies to COVID-19. Based on antibody patterns and COVID-19 incidence, these subjects fell into two distinct groups.
One group, which had only IgA antibodies, never succumbed to COVID-19. Participants in the other group had both IgG antibodies and T cells and contracted the disease. The acquired immune system also includes IgG antibodies and T cells, which recognize viruses, for example, and protect us against them.
Those responsible for the study were, first, Christine Wennerås, Professor of Clinical Bacteriology at Sahlgrenska Academy, University of Gothenburg, and senior physician at Sahlgrenska University Hospital; and, second, Kristina Eriksson, Professor of Viral Immunology at Sahlgrenska Academy.
“We all have IgA. It’s found on the mucous membranes, and COVID-19 is an infection that spreads via those membranes. We thought it was important to investigate what happened when completely healthy people encountered the coronavirus before vaccines became available,” Wennerås says.
“Of the participants in our study, none who contracted Covid-19 required hospitalization. Much other research has concerned the most seriously ill patients, who have been hospitalized and need intensive care.”
Focus on health factors
The present study focused on identifying health factors that afford protection against COVID-19. Numerous factors were found through extensive questionnaire surveys, blood tests, and more. When a participant had nasal congestion, a cough, red eyes, changes in the sense of taste, or anything else that could be an infection, they had to answer questions and undergo a PCR test.
What the subjects who neither tested positive nor fell ill had in common were IgA antibodies, which bind to the coronavirus. Being female and having a respiratory allergy were other factors affording protection against becoming infected. However, the study does not support the idea that people without antibodies against COVID-19 have protective T cells.
“Many Covid-related research has been about IgG antibodies and T cells. Interestingly, when we examine other people's articles and tables, we find evidence for the conclusion we’ve arrived at about IgA. But it’s not something those studies have highlighted,” Wennerås says.