COVID-19 recovered people living in nursing homes have high levels of protective antibodies three months after receiving the vaccine, in contrast to those who have not undergone the disease

Elderly have been really affected by the COVID-19 pandemic, which has already caused the death of almost 30,000 people living in nursing homes in Spain. Now, the results of a study carried out by the IrsiCaixa AIDS Research Institute -a center jointly promoted by the "la Caixa" Foundation and the Department of Health of the Generalitat de Catalunya- and the North Metropolitan Primary Care of the Institut Català de la Salut (ICS), indicate that the levels of neutralizing antibodies -characterized by their protective effect- of people over 65 years old living in nursing homes and who have been vaccinated is much higher in those people who have also passed the SARS-CoV-2 infection, compared to those who have not passed it. In fact, these last ones show very low levels of protective antibodies three months after receiving the full course of the vaccine. The results obtained in the study, which is being carried out with the support of the solidarity initiative YoMeCorono and the Glòria Soler Foundation, highlight the need to monitor the immune response of this most vulnerable group and, if necessary, adapt the vaccination schedule to achieve a higher level of antibodies to protect this group of people from infection.

The vaccination campaign has been a turning point in the course of the pandemic. However, it is now necessary to understand how long the protection lasts in order to be able to foresee and anticipate new outbreaks of the disease. So far, most studies suggest that this protective response is maintained at least one year after infection, but most of these studies have been carried out in people under 65 years of age. "The response of elderly people to vaccines or infections is different because their immune system is aged and the cells that should protect them are less efficient," explains Marta Massanella, principal investigator of the Translational Research in Immunology and Aging (TRIA) group at IrsiCaixa and co-coordinator of the project with Núria Prat, director of the Metropolitan Primary Care North of the ICS. "We want to find out how long the protection of people living in nursing homes lasts in order to help this more vulnerable group," adds Prat.

Passing the infection ensures better immune response

In order to evaluate the immune response of elderly, researchers followed 98 people living in 3 nursing homes in the Northern Metropolitan area of Catalonia. Among these, more than 80% were infected during the first wave of the pandemic and, later, all of them received the full course of the Pfizer vaccine. Blood samples were drawn from this entire group before vaccination and three months later, and in this way the levels of neutralizing antibodies generated by the infected and vaccinated individuals could be compared with those of those who had only been vaccinated. "The results we have obtained show that people who had not been infected have very low levels of neutralizing antibodies three months after vaccination and, moreover, these levels decrease as age increases," explains Macedonia Trigueros, predoctoral researcher at IrsiCaixa.

This contrasts with results from elderly people who had recovered COVID-19 before receiving the vaccine, who show a much stronger immune response. In fact, their total number of antibodies is much higher than that of a younger group of individuals. However, laboratory experiments have shown that few antibodies in older people are able to block infection, and thus the levels of protective antibodies eventually equal those of younger people. These data demonstrate that the quality of the immune response in the elderly is limited and highlight the ageing process that the immune system undergoes over time. This process is known as immunosenescence and reflects the loss of effectiveness of immune cells over the years.

Consider future vaccination strategies

This compromised immune response and a high probability of suffering from several additional chronic diseases means that elderly people are more likely to suffer from severe COVID-19. "With the current epidemiological situation, we observe that this most vulnerable group is once again affected," says Mar Isnard, head of nursing at the ICS Metropolitan North Primary Care.

The results of this study are a first step towards understanding the extent to which elderly people are protected and highlight the importance of continuing to monitor their immune response. "The data make us consider the need to adapt the vaccination schedule received by this age group, especially those who have not passed the infection. Now we need to study the best vaccination schedule and continue research to understand the evolution of the immune response beyond the first three months," concludes Bonaventura Clotet, director of IrsiCaixa and Head of the Infectious Diseases Department at the Germans Trias i Pujol Hospital.