Both infection and vaccination against SARS-CoV-2 contribute to building a population’s immunity against the virus – an important piece of information for deciding when and to whom to apply booster vaccinations. The easiest strategy to assess such immunity is to perform seroepidemiological studies (that is, to quantify virus-specific antibodies in a certain population group), although immunity against a pathogen goes beyond antibodies.
It is known that people with disorders such as depression, chronic stress or schizophrenia have a lower response to vaccination in general
“Most of the serological studies carried out after vaccination against COVID-19 focused on specific groups such as health personnel, did not distinguish between people with or without previous infection, or did not have clinical and immunological data of said infection,” explains Manolis Kogevinas , ISGlobal researcher and senior co-author of the study together with fellow ISGlobal researcher Carlota Dobaño.
In this study, the research team carried out a second measurement in a population cohort from Catalonia COVICAT-GCAT (GCAT | Genomes for Life Project) six months after the start of vaccination (the first was just after the first lockdown) to monitor the level and type of antibodies against five viral antigens: the entire Spike (S) protein, the RBD receptor binding domain, the S2 fragment, the entire Nucleocapsid (N) protein, or the N-terminal fragment.
They also used information obtained from a questionnaire and health records to identify factors that potentially determine the magnitude and duration of response in unvaccinated, vaccinated, or vaccinated and infected persons. 1,076 people were included in the analysis, between 43 and 72 years of age.
The results yield three main conclusions:
Antibodies were no longer detected in 36% of infected but unvaccinated people one year after infection, particularly in people over 60 years of age and smokers.
In people with prior infection, vaccination induced significantly higher antibody levels than in people without prior infection. These levels were strongly associated with the magnitude of the response during infection.
“Our data underscores the importance of vaccinating people, even if they have been previously infected, and confirms that hybrid immunity is superior and longer lasting. This means that people who have been vaccinated but have not passed the infection they would need a reinforcement before those who have passed it »says Marianna Karachaliou, first author of the study together with Gemma Moncunill.
The factor most strongly associated with the level of antibodies is the type of vaccine. The Spikevax de Moderna was the one that generated the most antibodies. In addition, other factors also seem to play a role: people over 60 years of age or with mental illness had lower levels of antibodies after vaccination. “The association between mental health and antibody response requires further investigation, but it is known that people with disorders such as depression, chronic stress or schizophrenia they have one least response vaccination in general”, explains Dobaño.
Among vaccinated people, only 2.1% had no antibodies at the time of testing and approximately 1% had a post-vaccination infection. “However, it is necessary to point out that this study was done before the variant omicron became dominant”, concludes Kogevinas