A team of researchers from the University of Gothenburg has just taken another step toward understanding how the immune system develops resistance against COVID-19.

For six months, the researchers at the University’s Sahlgrenska Academy investigated 156 employees from five primary care health facilities who were recruited during April and May 2020. None of these employees had been vaccinated against COVID-19, and the majority of them had to work with infected patients on a daily basis during the height of the pandemic.

They identified IgA (immunoglobulin A) in the respiratory tracts of several of the personnel who didn’t catch COVID-19, which could mean they had an antidote in their immune systems all this time.

These antibodies are found naturally in mucous membrane secretions in the airways and gastrointestinal tract, where they protect the body by binding to viruses and other invading organisms.

An antidote in the immune system

COVID-19, an infectious disease caused by the SARS-CoV-2 virus, has claimed the lives of more than 6 million people since the start of the pandemic in early 2020. In fact, some researchers say the true number of lives lost to the COVID-19 by 31 December 2021 was 18.2 million, which is more than three times the official death toll.

The disease appears to affect some people more severely than others, with some experiencing very minor symptoms and others being hospitalized and requiring aid in breathing. The current study aimed to uncover health factors that appeared to offer COVID-19 protection for the unvaccinated.

“We all have IgA,” said Christine Wennerås, Professor of Clinical Bacteriology at Sahlgrenska Academy, University of Gothenburg, and senior physician at Sahlgrenska University Hospital, who is part of the research team. “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.”

“Of the participants in our study, none whom contracted COVID-19 required hospitalization,” she continued. “A lot of other research has concerned the most seriously ill patients, who have been hospitalized and in need of intensive care.”

Health factors

According to the results of the study published in the European Journal of Immunology, a third of the care workers developed antibodies to COVID-19, and they fell into two distinct groups based on antibody patterns and COVID-19 incidence.

One group that exclusively possessed IgA antibodies never succumbed to COVID-19. Participants in the other group had IgG antibodies as well as T cells and got the sickness.

The participants who did not test positive or were unwell all had IgA antibodies. Other characteristics that seemed to provide protection against infection were being female and having a respiratory allergy.

The data, however, does not support the notion that those who do not have antibodies against COVID-19 have protective T cells, which are a part of the immune system that focuses on specific foreign particles.