New Delhi— A team of UK researchers has found compelling evidence that “immunity debt,” brought on by prolonged public health restrictions during the Covid-19 pandemic, is contributing to changes in global flu transmission patterns.
“Immunity debt” refers to a phenomenon in which populations become more vulnerable to infections after extended periods of reduced exposure to common pathogens. Although this theory had been widely discussed, there was limited evidence supporting it—until now.
During the Covid-19 pandemic, countries around the world implemented strict public health measures such as lockdowns, social distancing, mask mandates, and travel bans. While these strategies were essential in curbing the spread of Covid-19, they also led to a significant decline in other respiratory illnesses, including influenza.
However, since these restrictions were lifted, nations across the globe have experienced a sharp rise in flu cases.
Researchers caution that this “immunity debt” could result in major flu outbreaks in the years following a pandemic, as populations reacquire susceptibility to circulating viruses.
“Our findings provide evidence for the ‘immunity debt’ hypothesis,” said senior author Daniel Prieto-Alhambra, Professor of Pharmaco- and Device Epidemiology at NDORMS, University of Oxford. “By limiting flu exposure over the past few years, we’ve built up a more vulnerable population that is now experiencing a significant rebound in infections. Fortunately, strategies are available to mitigate the impact on high-risk groups, and flu vaccination should be strongly encouraged among them.”
The study, published in Advanced Science, analyzed global influenza data from 116 countries spanning 2012 to 2024. The researchers found that during the Covid-19 restriction periods, flu cases dropped by an average of 46 percent worldwide. However, in 2022—the first winter after restrictions were lifted—flu cases surged by an average of 132 percent compared to pre-pandemic levels.
Notably, the severity of this rebound was linked to the stringency of a country’s Covid-19 measures. Nations with more rigorous lockdowns and distancing policies experienced the largest post-pandemic flu spikes.
The researchers urged public health authorities to consider the risk of immunity debt when developing future pandemic preparedness and response strategies. (Source: IANS)
