1 in 3 infected, unvaccinated people no longer have detectable antibodies 1year later

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In a study from ISGlobal, scientists found 1 in 3 infected, unvaccinated people no longer have antibodies 1year after infection.

Both infection and vaccination against COVID-19 contribute to building a population’s immunity to the virus—an important factor for deciding when and to whom booster shots should be offered.

Although immunity against a pathogen is more than antibodies, the easiest strategy for assessing population immunity is to perform seroepidemiological studies (i.e., quantifying virus-specific antibodies in a given population group).

In this study, the team used data in a study Catalonia (COVICAT study—GCAT cohort) six months after the start of the vaccination campaign, to monitor the level and type of antibodies against five viral antigens.

In total, 1,076 people, aged 43 to 72 years, were included in the analysis.

The results showed three main conclusions: First, in 36% of infected but unvaccinated persons, antibodies were no longer detectable almost a year after the infection, particularly in those older than 60 years and who were smokers.

Second, that vaccination induced much higher antibody levels in people who had had prior infection, as compared to those without prior infection; and that these levels were strongly associated with the magnitude of the response during the infection.

Third, the factor most strongly associated with the level of antibodies is the type of vaccine—Moderna’s Spikevax generated the highest levels of antibodies.

Other factors also appear to play a role: People older than 60 or with mental illness had lower antibody levels post-vaccination.

The association between mental health and antibody responses requires further research, but it is known that people with disorders such as depression, chronic stress or schizophrenia have a lower response to vaccination in general.

Among those vaccinated, only 2.1% had no antibodies at the time of testing and approximately 1% had a breakthrough infection.

The finding underlines the need to get vaccinated despite having been infected and confirms that hybrid immunity (vaccination plus infection) is more robust and long-lasting.

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The study was conducted by Manolis Kogevinas et al and published in BMC Medicine.

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