36% of covid-infected, unvaccinated individuals have no antibodies one year later

The 36% of people in between 43 and 72 years old that were infected with covid-19 a year ago and that were not vaccinated already have no detectable antibodies. It occurs mostly in those over 60 years of age and smokers. A study led by the Barcelona Institute for Global Health (ISGlobal), sponsored by the La Caixa Foundation, on the seroprevalence in the population of Catalonia. underlines the need for vaccination despite having been infected and confirms that, in these cases, hybrid immunity (vaccination plus infection) is greater and longer lasting. The research, in which the German Trias i Pujol Institute (IGTP) collaborated, with the support of the Daniel Bravo Andreu Private Foundation (FPDBA), has been published in the journal. ‘BMC Medicine’.

To analyze the importance of the covid-19 vaccine it is necessary to take into account the “diversity” of the population. “To the people healthy adults, natural immunity lasts longer. However, in the elderly, disabled or with some comorbidity, we see that the loss of antibodies after being naturally infected occurs in one in three. That’s why it’s important here to emphasize vaccination, explains to this newspaper Carlota Dobaño, head of the immunology group at ISGlobal.

Both the infection as the vaccination against SARS-CoV-2 contribute to building a population’s immunity to the virus. This is important for deciding when and whom to vaccinate. to give booster vaccines. Seroepidemiological studies help to assess immunity in specific population groups. Most of the studies following covid-19 vaccination focused on specific groups such as health care personnel and did not distinguish between persons with or without previous infection. The ISGlobal study tracked the levels and types of antibodies to 1,076 people aged 43 to 72 years. in two phases: the first between June and November 2020, and the second between May and July 2021.

Three conclusions

The results yielded three main conclusions. The first is that in the 36% of infected but unvaccinated persons. antibodies were no longer detectable one year after infection, especially in persons older than 60 years and smokers. “Particularly, those over 60 years of age and with comorbidities and smokers -tobacco is another risk factor- it is easier for them to lose the antibodies induced by the infection, and that is why they should be vaccinated with booster doses,” explains Dobaño.

The second conclusion is that, in the persons with previous infection, vaccination produced levels of antibodies. considerably higher than in persons without previous infection. “Our data underscore the importance of vaccinating people, even if they have been previously infected, and they confirm that hybrid immunity is superior and more durable.. This means that people who have been vaccinated but have not passed the infection would need a booster earlier than those who have,” he says, Marianna Karachalioufirst author of the study together with Gemma Moncunill

The third conclusion is that the factor most strongly associated with antibody level is the type of vaccine.. Modern was the one that generated the most antibodies. In addition, they also seem to influence other factors: the persons over 60 years of age or with mental illness had lower antibody levels after vaccination. “The association between mental health and antibody response requires further investigation, but people with disorders such as depression, chronic stress or schizophrenia are known to have a lower response to vaccination in general,” notes Dobaño.

However, experts still do not know “what is the minimum number of antibodies needed” to be protected. “Yes, it is known for other vaccines, such as hepatitis B. But, in covid-19, this is still a matter of research,” concludes the ISGlobal researcher.