High Mucosal Antibodies in Airways Reduce COVID-19 Reinfection by 55%

One of the greatest questions throughout the COVID-19 pandemic has been reinfection. How likely is it? Will a reinfection be more or less severe than the first infection? How will the emergence of new variants affect reinfection rates?

A new study found that contracting the Omicron COVID-19 variant generated durable mucosal antibodies that significantly reduce the risk of reinfection.

Mucosal immunity is known to protect against other respiratory infections. The study, published in The Lancet Infectious Diseases, examined how high levels of mucosal immunoglobulin-A antibodies (M-IgA) protect against COVID-19 reinfection.

"Antibodies in the blood protect from severe disease,” said Charlotte Thålin, MD, an associate professor at the Danderyd Hospital Department of Clinical Sciences and a lead author of the study. “But if we aim to limit infection, viral transmission and the emergence of new SARS-CoV-2 variants, we need to reinforce our immunity at the mucosal surface, which is the viral point of entry.”

The investigators recruited 2149 health care employees from the Danderyd Hospital in Sweden. Since spring of 2022, the study participants’ COVID-19 immune responses have been monitored via regular blood tests and airway screenings.

A sub-study, conducted during January and February 2022, screened 338 health care worker who were triple vaccinated (2 doses of a primary COVID-19 vaccine series and 1 booster dose). The study found that participants with high mucosal IgA antibodies in their airways had half the risk of Omicron infection, compared to those with little to no antibodies in their airways.

High concentrations of nasal mucosal SARS-CoV-2 WT spike immunoglobulin-A (M-IgA) have previously proven effective against Omicron infection over a 4-week study period. With this research, the investigators confirmed that patients with M-IgA concentrations of at least the 75th percentile upon enrolment had a 55% reduced risk of BA.1, BA.2, or BA.5 symptomatic breakthrough infection over an 8-month follow-up period.

Even a mild Omicron infection yielded over a 40-fold increase in M-IgA antibodies, results that pave the way for more research into the protection granted by a durable mucosal IgA antibody response in the airways.

“The hope is that a nasal vaccine may generate mucosal immune responses similar to those seen after infection, and thereby block the transmission chain,” said Thålin.