Antibodies produced in the nose decline nine months after COVID-19 infection, while antibodies found in the blood last at least a year, a new study has found.
Antibodies in the nasal fluid, known as immunoglobulin A, or IgA, provide first-line defence against COVID-19 by blocking SARS-CoV-2 virus when it first enters the respiratory tract. These antibodies are very effective in preventing the virus from entering cells and causing infection.
However, the investigators found that the nasal antibodies were only present in those recently infected and were particularly short-lived against the Omicron variant, compared to earlier variants.
The research was led by teams from Imperial College London and the University of Liverpool.
Based on the study, the researchers have called for the next generation of vaccines to include nasal spray or inhaled vaccines that target these antibodies more effectively, which could potentially reduce infection and transmission.
These new findings, published in the journal eBioMedicine, may explain why people who have recovered from COVID are at risk of reinfection especially with Omicron and its sub variants.
The study also found that vaccination is very effective in creating and boosting antibodies in the blood, which prevent severe disease, but had very little effect on nasal IgA levels.
"Before our study, it was unclear how long these important nasal antibodies lasted. Our study found durable immune responses after infection and vaccination, but these key nasal antibodies were shorter-lived than those in the blood.
"While blood antibodies help to protect against disease, nasal antibodies can prevent infection altogether. This might be an important factor behind repeat infections with the SARS-CoV-2 virus and its new variants," said Dr Felicity Liew, first author of the study.
The researchers note that more studies that directly analyse these nasal antibodies and reinfections are needed to confirm their results.
The research studied almost 450 people who had been admitted to hospitals with COVID-19 between February 2020 and March 2021, before the emergence of the Omicron variant and prior to vaccine rollout.
"Our results highlight a need for nasal spray vaccines that can boost these local antibodies in the nose and lungs. Such vaccines might be able to prevent people from getting infected with the SARS-CoV-2 virus and reduce transmission of the virus between people.
"This could help us to better control the pandemic and stop new variants emerging," said Peter Openshaw, co-senior author of the study.
"Our current vaccines are designed to reduce severe disease and death and are dramatically effective in this aim. It's now essential to also develop nasal spray vaccines that can provide better protection against infection," said Openshaw.
The study analysed antibodies of the participants to understand how long nasal antibodies lasted, compared with antibodies found in the blood. They also studied the effect of subsequent COVID-19 vaccines on antibodies in the nose and blood.
They also found that blood antibodies from participants continued to bind the original SARS-CoV-2 virus, and the Delta and Omicron variants a year after infection, but found that booster vaccines are needed to maintain this immunity.