“Duty of immunity” is a false and dangerous concept

The writer is a science commentator

Respiratory syncytial virus is a little-known and hard-to-write seasonal scourge that, like the flu, affects children and the elderly most. It usually causes a cough and a cold, but can cause serious breathing difficulties in a small number of babies.

RSV is so common that more than 80 per cent of UK children are infected by their second birthday – but the number of cases has fallen dramatically during the Covid-19 pandemic. Measures such as masking, plus school and daycare closures aimed at slowing the spread of Covid, are also halting infection rates. Now the virus is resurgent, especially in the United States, the wave is hitting faster than expected.

This has fueled speculation that the mitigation of the pandemic, including lockdowns, has created a harmful “immunity debt”, leaving children vulnerable to the usual cut and thrust of viral infections. But scientists rejected the concept applied to individual immunity as a misdirection.

The debate surrounding debt immunity shows how easy it is for a plausible-sounding theory to spread as disinformation. In this case, disinformation risks feeding revisionist narratives that Covid measures are doing more harm than good, while promoting unsubstantiated claims that infections are clinically beneficial for children.

Professor Peter Openshaw, a respiratory doctor and immunologist at Imperial College London who studies RSV and flu, said the current “high and unseasonal” RSV wave is thought to be a result of lockdowns, which have reduced immunity in children, parents and carers. leading to more infections.

But to frame it as an immunity debt, warns Openshaw, is mistakenly suggesting that “immunity is something we have to invest in, and that by protecting ourselves from infection, we are running up a deficit that will eventually have to be repaid. It would not be a good message for public health: if this idea were followed logically, we would still have open sewers and be drinking cholera-contaminated water.” Delaying RSV infection may actually be beneficial, he adds, because the virus is most deadly for babies younger than six months. Globally, one in 50 deaths among children under the age of five is related to RSV.

Deborah Dunn-Walters, professor of immunology at the University of Surrey, said it was important to distinguish between individual and population immunity (herd immunity) when examining how pandemic measures could alter the spread of non-Covid diseases. A smaller pool of infected people during a pandemic may lead to a larger pool of susceptible people after measures are lifted. A decline in population immunity may increase the rate simply because there are more people to infect (other factors, including weather and virus severity, may also affect transmission).

However, there is no evidence that a person is worse off for having avoided an earlier infection. “Immunity as an individual concept is not recognized in immunology,” says Dunn-Walters. “The immune system is not seen as a muscle that needs to be used all the time to stay in shape, and if anything, it’s the other way around.” He adds that the constant onslaught of common pathogens like cytomegalovirus means the immune system begins to function and weaken with age. He rejects the idea that infection is beneficial to health, saying vaccination is a safer way to boost population immunity.

Steven Griffin, a virologist at the University of Leeds who believes that pediatric pandemic vaccines are underused, argues that we are still too complacent about childhood respiratory illnesses. Although there is no vaccine for RSV, Griffin admits, “we be able vaccinate against both flu and Covid – but we don’t. Changing that norm, he says, could help neutralize the worst effects of the “triple disease” predicted this winter. The UK’s Health Safety Agency recommends that eligible children receive the flu vaccine.

The theory of debt immunity has broad appeal because it can be used in many ways. It seems to intuitively explain the current wave of respiratory diseases. This is attractive to those who want to reduce disease in children and advocates of infection rather than vaccination. This provides a post-hoc justification for opposing measures such as masking, even though the evidence suggests that such measures prevent Covid and indeed influenza.

Immunity Debt also plays with the idea that the ebb and flow of childhood diseases is best left to nature—until you remember that the entire childhood vaccination schedule is about keeping nature’s worst at bay.