A new study finds 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 defence against COVID-19 by blocking 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 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.
These new findings — which are published in eBioMedicine — 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.
First author of the study, Dr Felicity Liew, from the National Heart and Lung Institute at Imperial College London, said: “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.”
The researchers note that studies that directly study these nasal antibodies and reinfections are needed to confirm their results.
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