Why do we get reinfected with COVID-19? A new study identifies the 5 main causes

In recent weeks, COVID-19 transmission has slightly accelerated. In fact, in Catalonia, an estimated incidence of 78 cases per 100,000 inhabitants has been reached. In this context, a new study, published in the scientific journal Viruses and co-led by the Fight Infections Foundation and IrsiCaixa – a centre jointly promoted by the "la Caixa" Foundation and the Department of Health of the Generalitat de Catalunya – in collaboration with the Germans Trias Hospital, provides new evidence about the factors driving SARS-CoV-2 reinfections.

The study, which included the analysis of clinical data and samples provided by the hospital, reveals that the genetic evolution of the virus is the main driver of reinfections. The emergence of new variants, such as Delta or Omicron, is directly associated with the peaks of reinfection observed during the pandemic.

" This study allows us to better characterize the factors that increase the likelihood of reinfection, something especially relevant now, as we are seeing spikes in infections," say the principal investigator of IrsiCaixa Marta Massanella and the doctor and researcher of the Fight Infections Foundation, José Ramón Santos, both leaders of the study.

Francisco Muñoz-López, first author of the article and predoctoral researcher at IrsiCaixa, underlines the magnitude of the analysis carried out: " We studied the cases of over 3,000 people to better understand when reinfections occur, in order to seek possible solutions."

1. The evolution of the virus is the main cause of reinfections

The study confirms that viral evolution is the leading cause of reinfections. The emergence of new variants is closely linked to reinfection peaks, highlighting the need for ongoing genomic surveillance.

2. Chronic diseases increase the risk of reinfection

In turn, chronic diseases increase the risk of getting reinfected. The study observed that more than 86% of participants had at least one chronic condition, even among those under 26 years of age. These illnesses not only weaken the immune system but also increase exposure to the virus due to more frequent visits to healthcare facilities.

3. The average interval between infections is one year

Another conclusion is that immunity wanes over time. Specifically, the average interval between infections was approximately one year, due to both the progressive loss of immunity and the emergence of new variants.

4. Protection against reinfection drops 40-100 days after vaccination

Vaccination has been shown to protect against severe illness but not necessarily against reinfection. In this sense, vaccines have proven to be effective in preventing hospitalizations and severe disease, but their protection against new infections is limited. According to the study, protection against reinfection is significantly reduced 40 to 100 days after vaccination.

5. Social and gender factors also play a role

Most of the participants in the study were women, probably because of their predominant role in care and their greater contact with the health system.

"These results can be very useful for health authorities when designing vaccination strategies that are more adapted to the current reality," concludes the research team.