A prospective seroprevalence study in the Catalan population emphasizes the need for vaccination despite infection, and confirms that hybrid immunity (vaccination plus infection) is more robust and long-lasting. The study, which was co-led by the Barcelona Global Institute with support from the Daniel Bravo Andrew Foundation (FDBA), was published in Medicine BMC.
Both infection and vaccination against SARS-CoV-2 contribute to building a population’s immunity to the virus – an important factor in determining when and to whom booster injections should be given. Although immunity to a pathogen is more than an antibody, the easiest strategy for assessing a population’s immunity is to conduct serological epidemiological studies (that is, to measure virus-specific antibodies in a given population).
Manolis Kojvinas, ISGlobal, explains that “most serological studies conducted after vaccination against COVID-19 focused on specific groups such as health care workers, and did not distinguish between people with or without prior infection, or had no clinical data and immunity to infection.” Researcher and senior author on the study with Carlota Dobaño, also a researcher at ISGlobal.
In this study, the research team performed a second measurement in a Catalan population (the COVICAT study – GCAT cohort) six months after the start of the vaccination campaign (the first was just after the first confinement), to monitor the level and type of antibodies against five viral antigens (Spike protein) S) completely, the RBD receptor-binding domain, the S2 fragment, the complete nucleocaspid (N) protein, or the N-terminal fragment). They also used information from the questionnaire and health records to identify potential factors that determine the magnitude and duration of an antibody response in unvaccinated, vaccinated, or vaccinated and infected people. A total of 1,076 people, aged between 43 and 72 years, were included in the analysis.
The results yielded three main conclusions: First, in 36% of infected but unvaccinated subjects, antibodies could no longer be detected approximately one year after infection, especially in those over 60 years of age and smokers.
Second, this vaccination induced significantly higher levels of antibodies in people who had had previous infections, compared to those who had not had a previous infection; And that these levels were strongly correlated with the size of the response during infection. “Our data underscore the importance of vaccinating people even if they were previously infected, and confirm that hybrid immunity is better and more durable. This means that people who have been vaccinated but not infected will need a booster dose earlier than those who have been infected,” notes Mariana Carraccilio, author First to study with Gemma Monconnell.
Third, the factor most closely related to antibody level is the type of vaccine – Moderna Spikevax produced the highest antibody levels. Other factors appear to play a role as well: People older than 60 or with mental illness have lower levels of antibodies after vaccination. “The association between mental health and antibody responses requires further investigation, but people with disorders such as depression, chronic stress, or schizophrenia are known to have a lower response to vaccination overall,” Dobaño explains.
Of those vaccinated, only 2.1% had no antibodies at the time of testing and about 1% had a breakthrough infection. “However, it should be noted that this study was conducted before the Omicron variant became dominant,” Kogevinas warns.