The author is a scientific commentator
Respiratory syncytial virus is a little-known and hard-to-spell seasonal plague that, like the flu, hits children and the elderly the hardest. It usually triggers coughs and colds, but can cause severe breathing difficulties in a small minority of infants.
RSV is so common that more than 80% of British children are infected before their second birthday – but the number of cases has dropped during the Covid-19 pandemic. Measures such as masking, as well as the closure of schools and nurseries, intended to slow the spread of Covid, have also curbed infection rates. Now the virus is resurging, particularly in the United States, with the wave hitting earlier than expected.
This has fueled speculation that pandemic mitigations, including lockdowns, have created a harmful ‘immunity debt’, with children remaining vulnerable due to a lack of exposure to the usual cut and push. viral infections. But scientists have dismissed the concept, as applied to individual immunity, as flawed.
The swirling discussion around immunity debt shows how easy it is for a plausible theory to circulate as misinformation. In this case, misinformation risks promoting the unfounded claim that infections are clinically beneficial to children, as well as fueling the revisionist narrative that Covid measures have done more harm than good.
Professor Peter Openshaw, a respiratory physician and immunologist who studies RSV and influenza at Imperial College London, says the current “high and unseasonal” surge of RSV is believed to be the result of lockdowns causing levels of immunity in children, parents and caregivers, setting the stage for more infections.
But to frame this as an immunity debt, Openshaw warns, erroneously suggests “that immunity is something we have to invest in, and that by protecting ourselves from infection we accumulate a deficit that ultimately has to be reimbursed”. That wouldn’t be a good public health message: we’d still have open sewers and we’d be drinking cholera-contaminated water if this idea were taken to its logical conclusion. Delaying RSV infection may actually be beneficial, he adds, because the virus is deadliest for infants under six months of age. Globally in children under five, one in 50 deaths is attributable to RSV.
Deborah Dunn-Walters, professor of immunology at the University of Surrey, says it is essential to distinguish between individual immunity and population immunity (herd immunity) when considering how whose pandemic measures may have altered the spread of non-Covid diseases. A smaller pool of people infected during the pandemic may lead, after measures are lifted, to a larger pool of susceptible people. This decline in population immunity may fuel a surge simply because there are more people likely to be infected (other factors, including weather and the severity of the virus, may also affect transmission).
But there is no evidence that an individual is worse off for having avoided a previous infection. “Immune debt as an individual concept is not recognized in immunology,” says Dunn-Walters. “The immune system is not seen as a muscle that must be used all the time to stay in shape and, on the contrary, it is rather the opposite.” The constant onslaught of common pathogens such as cytomegalovirus, she adds, means the immune system begins to malfunction and slack off with age. She rejects the idea that infection is somehow good for your health, saying vaccination is a much safer way to boost population immunity.
Stephen Griffin, a virologist at the University of Leeds who believes pediatric pandemic vaccines have been underutilized, says we are still too complacent about childhood respiratory disease. Although there is no vaccine against RSV, acknowledges Griffin, “we box vaccinate against both flu and Covid – and yet we don’t. Changing that norm, he says, could help neutralize the worst effects of a “triple epidemic” expected this winter. The UK Health Security Agency recommends that eligible children receive the flu vaccine.
The immunity debt theory is very appealing because it can be used in so many ways. This seems to intuitively explain the current wave of respiratory diseases. It appeals to those who downplay the importance of disease in children and those who advocate infection over vaccination. It provides post-hoc justification for opposing measures such as masking, even though evidence suggests such measures have curbed Covid and all but banished the flu.
Immune debt also plays into the idea that the ebb and flow of childhood illnesses are best left to nature – until one remembers that the whole childhood immunization schedule is to keep nature’s worst from a distance.