Covid lockdowns saved lives, but did they make us sicker?

medium nocaption121144541It’s a cacophony of coughs and sneezes at the out-patient department (OPD) of a top hospital chain in Delhi. “I suffered a bout of fever and cough two weeks ago. Even though the fever subsided within three days, the cough stayed,” says a patient waiting to see the doctor. Another one, sitting nearby, adds, “I would rarely fall sick during season change earlier. But after Covid, it has become routine. I wonder why this is happening.”Such refrains have become common among people across the country as they make regular rounds of clinics due to fever, cough and other symptoms associated with seasonal illnesses post-Covid lockdowns. Though many theories have emerged to explain this phenomenon — including long Covid in which debilitating health problems can persist for months after recovering— some studies link the increased frequency and severity of such common infections to an ‘immunity debt’.What is immunity debt?The term first found mention in mid-2021, after New Zealand saw a sudden surge in hospitalisations as babies caught the deadly Respiratory Syntactical Virus (RSV). Experts say ‘immunity debt’ refers to a hypothesised reduction in population-level immunity owing to lack of regular exposure to disease-causing bacteria and viruses.According to a study last month by researchers from the University of Oxford and Beijing’s Peking University, the measures that kept us safe during lockdowns — such as masking, washing hands, and social distancing throughout the pandemic — drastically reduced exposure to not just Covid-19, but also other disease-causing pathogens. When the masks came off and we left the safety of our homes, the pathogens caused a spurt in infections. medium nocaption121141047“The degree of immunity debt was linked to how stringent a country’s Covid-19 restrictions had been during the pandemic. Places that implemented the most severe lockdowns and social distancing measures tended to see the largest flu resurgences later,” wrote study author and Peking University scholar Li Chen. Co-author and Oxford epidemiologist Daniel Prieto-Alhambra wrote, “By limiting flu exposure over the past few years, we’ve built up a more vulnerable population that is now seeing a major rebound in infections.”The study, published in the journal Advanced Science, analysed global flu data from 116 countries between 2012 and 2024, including India. Researchers found that during Covid-19 restriction periods, flu cases dropped by an average of 46% worldwide. However, in 2022, the first winter after restrictions were lifted, flu cases surged by an average of 132% above pre-pandemic levels. It warns that an ‘immunity debt’ could lead to major flu outbreaks in the years after a pandemic as populations regain susceptibility to other viruses.In India, a nationwide lockdown was enforced in four phases, from March to May 2020, to curb the spread of the virus. It was lifted from June 1, 2020, but orders to ensure physical distancing remained in place for a much longer period. Dr Suranjit Chatterjee, senior consultant, internal medicine at Delhi’s Apollo hospital, says the duration and severity of common infections like flu, cold, and RSV (which causes cold-like symptoms) has certainly gone up post pandemic. But Dr Chatterjee adds that more research was needed to link it to an ‘immunity debt’. “More frequent and prolonged infections due to common bacteria and viruses — for example, upper respiratory tract infections — could also be due to long Covid or persistent symptoms of Covid-19,” says Dr Rommel Tickoo, director of internal medicine at Max Hospital, New Delhi. A study by the analytics firm Airfinity and Bloomberg conducted last year showed that since 2020, more than 40 countries have seen at least one disease outbreak peak at levels ten times worse than the pre-Covid baseline. It cited the return of measles — declared eliminated in the US in 2000 — while whooping cough is on the rise too. However, experts say this could be indicative of the anti-vaccine sentiments which led to children missing out on crucial jabs.Does the theory hold ground?Dr N K Mehra, an immunologist and emeritus scientist at the Indian Council of Medical Research (ICMR), says the continued debate on immunity debt being responsible for a transient increase in seasonal infections was against the fundamental concept of ‘immunological memory’.“Once our body is exposed to a virus either through infection or vaccination, it develops generational immune memory which protects him or her from further infection of the same antigen. How long post-infection/vaccination immunity lasts varies from one virus to another. For flu viruses, infection in one season may or may not offer protection in the next, depending on how closely related the two strains are,” Dr Mehra says. ShowQuotesA 2022 study by the University of New South Wales in Australia had found that some people had an overactive immune function (where the immune system reacts excessively even to mild threats, leading to allergies and a host of other health issues) till several months after suffering from Covid. But those were isolated cases, researchers said, and hardly accounted for extensive immune impairment induced by Covid.Not everyone is convinced. Michael Levin, professor of paediatrics and international child health at Imperial College, London told the Guardian that kids and adults do build up a repertoire of immunity from exposure. “It’s plausible that we may now have a population that has met fewer common viruses and is, therefore, more susceptible (to them). Moreover, if fewer people have such immunity, there will be more transmission in the population,” he told the newspaper. However, he added that many times, we don’t really know how much and whether repeated exposure is at all needed to sustain immunity. For instance, in diseases such as smallpox and measles, just one infection usually gives lifelong protection.Vaccines to clear ‘debts’Nonetheless, a more proactive way of curbing the sudden surge of infections would be to enhance protocols for vaccine-preventable diseases. For, even if there is a perceived ‘immunity debt’, vaccines could tackle that. Dr Shuchin Bajaj of Ujala Cygnus Healthcare says future pandemic strategies must balance non-pharmaceutical interventions with immunity preservation, especially for endemic infections. “It would be wiser to have phased relaxation, off-season vaccination, and preparedness for post-pandemic surges in non-target pathogens,” he adds.