The number of antibodies present in the nasal fluid is reduced nine months after being infected with covid-19, while the antibodies in the blood last for less than a year, according to a new study published in the journal eBioMedicine .
Immunoglobulin A (IgA), the name given to the antibodies in the nose, provides a first-line defense against covid-19 since it blocks the SARS-CoV-2 virus when it enters the respiratory tract. These defenses are very effective in preventing the virus from entering cells and causing infection.
However, researchers have found that nasal antibodies are only present in newly infected people and are especially short-lived against the micron variant, compared to earlier variants.
This new study may explain why people who have recovered from covid are at risk of re-infection , and especially with omicron and its subvariants. Research has also revealed that vaccination is very effective at creating and boosting antibodies in the blood, which prevent severe disease, but the vaccine has very little effect on nasal IgA levels.
One of the study’s authors, Dr. Felicity Liew , of the National Heart and Lung Institute at Imperial College London, recalls that before the study it was not clear how long these important nasal antibodies lasted.
“While blood antibodies help protect us against the disease, nasal antibodies can prevent infection altogether. This could be a relevant factor behind the repeated infections with the SARS-CoV-2 virus and its new variants”, he says. However, the researchers say that specific studies of nasal antibodies and reinfections are needed to confirm their results.
The research, led by teams from Imperial College London and the University of Liverpool, looked at almost 450 people who had been hospitalized with COVID-19 between February 2020 and March 2021, before the variant appeared omicron and before the deployment of the vaccine.
The study also found that while current vaccines are effective at raising antibodies in the blood that prevent serious illness and death, they do not significantly increase nasal IgA antibodies.
The researchers are calling for the next vaccine development to include nasal sprays or inhaled vaccines that boost nasal IgA antibodies. They claim that this could reduce covid infections in a more effective way.
“It is now essential to develop nasal spray vaccines that can provide better protection against infection. It’s brilliant that current vaccines are allowing fewer people to become seriously ill, but it would be even better if we could prevent them from getting infected and passing on the virus,” says study co-author Professor Peter Openshaw, from the National Heart Institute and the Lungs of Imperial College London.
The study took samples when people were hospitalized, after six months and a year later. Since most people were vaccinated during the study, many samples were also taken before and after vaccination. The researchers say the participants’ sex, disease severity and age did not influence how long their nasal immunity lasted, but caution that their study was only conducted in people with severe disease that required hospitalization .