‘Immunity debt’ is a misguided and dangerous concept

The writer is a science commentator

Respiratory syncytial virus is a little-known and hard-to-spell seasonal scourge that, like the flu, most severely affects children and the elderly. It usually causes coughs and colds, but can cause severe breathing difficulties in a small minority of babies.

RSV is so common that more than 80 per cent of British children are infected before their second birthday – but cases have plummeted during the Covid-19 pandemic. Measures such as masking and closing schools and nurseries, designed to slow the spread of Covid, are also putting the brakes on infection rates. Now the virus is reviving, especially in the US, and the wave is hitting sooner than expected.

That has fueled speculation that pandemic mitigations, including lockdowns, have created a damaging “immunity debt,” with children left vulnerable from a lack of exposure to the usual cut and thrust of viral infections. But scientists have dismissed the concept as applied to individual immunity as misguided.

The discussion around immunity guilt shows how easy it is for a plausible-sounding theory to circulate as misinformation. In this case, disinformation threatens to promote the baseless claim that infections are clinically beneficial for children, feeding the revisionist narrative that Covid measures have done more harm than good.

Professor Peter Openshaw, a respiratory doctor and immunologist who studies RSV and flu at Imperial College London, says the current “high and unusual” RSV surge is the result of lockdowns reducing levels of immunity in children, parents and carers. paving the way for a greater number of infections.

But to view this as an immunity debt, Openshaw warns, is falsely suggesting “that immunity is something we need to invest in, and that by protecting ourselves from infection we build up a deficit that eventually has to be paid back. This would not be a good message for public health: we would still have open sewers and drink from water contaminated with cholera if this idea were taken to its logical conclusion.” Delaying RSV infection may even be beneficial, he adds, as the virus is deadliest for babies under six months old. Worldwide, one in 50 deaths among children under the age of five is due to RSV.

Deborah Dunn-Walters, professor of immunology at the University of Surrey, says it is critical to distinguish between individual and population (herd) immunity when exploring how pandemic measures can limit the spread of non-Covid diseases have changed. A smaller number of people who become infected during the pandemic could lead to a larger number of susceptible people after the lifting of the measures. That drop in population immunity could fuel a surge simply because more people are available to get infected (other factors, including weather and the severity of the virus, can also affect transmission).

But there is no evidence that a person is worse off for avoiding a previous infection. “Immunity debt 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, the opposite is true.” The constant onslaught of common pathogens like cytomegalovirus, she adds, means the immune system begins to falter and slacken with age. She rejects the idea that infection is somehow good for health, saying vaccination is a much safer way to build immunity for the population.

Stephen Griffin, a virologist at the University of Leeds who believes pandemic vaccines were underused in children, argues that we are still too complacent about childhood respiratory disease. While there is no vaccine for RSV, Griffin acknowledges, “we can vaccinating against both flu and Covid – and yet we don’t. Changing that standard, he says, could help neutralize the worst effects of a predicted “triplemic” this winter. The UK Health Security Agency advises that eligible children should receive the flu vaccine.

The immunity debt theory has broad appeal because it can be used in so many ways. It seems to intuitively explain the current wave of respiratory disease. It appeals to those who downplay childhood illness and to those who advocate infection over vaccination. It provides a post-hoc justification for resisting measures such as masking, although there is evidence that such measures have curbed Covid and virtually eradicated flu.

Immunity guilt also plays into the idea that the ebb and flow of childhood illness is best left to nature — until it is remembered that the entire childhood vaccination schedule is designed to keep nature’s worst at bay.

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