Immunity debt: Adverse effects after two years of pandemic

Immunity debt happens when the body has not been in contact with viruses or vaccines for a long time. In the case of COVID-19, the potential immunity debt is one year or longer (from one flu season to the next, for example), becoming more severe with each additional year without exposure to the usual viruses.

As a result, the body is more vulnerable to common bacterial and viral infections, like influenza, respiratory syncytial virus (RSV) and chicken pox. Our immune defenses are less effective in responding to bacterial attacks after a long period of inactivity. It’s a bit like an athlete who has been inactive for a long time and suddenly must compete for a medal at the Olympics.

Protective measures put in place around the world have greatly limited the spread of SARS-C0V-2. At the same time, they also reduced the transmission of other pathogens within the community. As a result, cases of influenza and other viruses dropped sharply during the pandemic, thereby helping to avoid overburdening health-care systems. In most Western countries, the number of cases of seasonal influenza plummeted by an unprecedented 99% during the winter of 2020.[1]

However, with the gradual resumption of activities, the reopening of schools and the phasing-out of health measures, viruses are once again circulating in the community, and some people with immunity debt are temporarily more at risk of these infections than others.

Senior citizens, immunosuppressed people and children are generally among the populations most vulnerable to pathogens. Following a long period of isolation during the COVID-19 pandemic, their vulnerability has only increased. During this time, there was less interest in annual immunization campaigns, leading to an added risk of a rise in hospitalizations among the elderly to treat seasonal infections.

In addition, people living with a chronic illness or organ failure are also at greater risk due to increased viral transmission in the population. Consequently, they should take special care during winter when infections peak.

For anyone at higher risk, it’s more important than ever to take advantage of annual vaccination campaigns, available free of charge.

Since winter 2021 and the gradual phasing-out of certain protective measures, cases of viral infection have exploded, especially among children.

Childhood diseases such as chickenpox and measles, which had seen a substantial decline in 2020, are making a major comeback. In addition, certain children who had previously avoided these diseases will now be infected when they are older and may be less able to deal with them. As a result, we can expect an increase in infections in the coming years, along with more complications and severe cases.[2]

Cases of respiratory syncytial virus (RSV) have also surged in in several countries, due to children not being exposed to this virus months earlier. RSV, which especially infects young children under the age of two, leads to hospitalization in one to three percent of cases. Quebec’s Institut national de la santé publique recorded more than 500 cases during the week of November 6, 2021 alone. In September of that year, cases were higher than in certain winters, even though RSV usually occurs from November to April.[3]

In the meantime, cases of airborne diseases will continue to climb sharply, and the immunity debt of certain groups may make them even more contagious.[1]