In a study from Imperial College London, scientists found that antibodies produced in the nose decline nine months after COVID-19 infection, while antibodies found in the blood last at least a year.
Antibodies in the nasal fluid (known as immunoglobulin A, or IgA) provide first-line defense against COVID-19 by blocking the SARS-CoV-2 virus when it first enters the respiratory tract.
These antibodies are very effective at preventing the virus from entering cells and causing infection.
However, the researchers 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.
These new findings may explain why people who have recovered from COVID are at risk of reinfection, and especially with omicron and its subvariants.
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.
The team says before their study, it was unclear how long these important nasal antibodies lasted.
This 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.
The researchers note that studies that directly study these nasal antibodies and reinfections are needed to confirm their results.
The research team studied almost 450 people who had been hospitalized with COVID-19 between February 2020 and March 2021, before the emergence of the omicron variant and prior to the vaccine rollout.
The study also found that whilst current vaccines are effective at boosting blood antibodies which can prevent serious illness and death, they do not significantly boost nasal IgA antibodies.
The researchers call for the next generation of vaccines to include nasal spray or inhaled vaccines that target these antibodies more effectively.
They say that vaccines capable of boosting these antibodies could potentially reduce infections more effectively and prevent transmission.
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The study was conducted by Dr. Felicity Liew et al and published in eBioMedicine.
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