Many Indians feel their infections go on longer after COVID. A new global study backs this with a theory called ‘immunity debt’ — but doctors remain divided on its validity.
It’s a cacophony of coughs and sneezes at the out-patient-department(OPD) of a top hospital chain in Delhi.
Such refrains have be come common among people across the country as they make regular rounds of clinics due to fever, cough and other symptoms associated with seasonal illness 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 round mention in mid-2021, after New Zealand saw a sudden surge in hospitalizations as babies caught the deadly Respiratory Syntactical Virus (RSV). Experts say ‘immunity debt’ refers to a hypothesized reduction in population-level immunity owing to a lack of regular exposure to disease-causing bacteria and viruses.
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.
“The degree of immunity debt was linked to how a stringent a country’s COVID-19 restrictions had been luring the pandemic. Places that implemented the most severe lockdowns and social distancing measures tended to see the largest flu resurgences later.”
“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.”
Global flu data from 116 countries between 2012 and 2024, including India. 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.
The duration and severity of common infections like flu, cold, and RSV (which causes cold-like symptoms) has certainly gone up post pandemic.
“More frequent and prolonged infections due to common bacteria and viruses — for example, upper respiratory tract infections — could be due to long Covid or persistent symptoms of COVID-19.”
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 not 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 THEORY HOLD GROUND?:
“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 the two strains are.”
Not everyone is convinced. Kids and adults do build up a repertoire of immunity of 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.”
However, many times, we don’t really know how much and whether repeated exposure is at all needed to sustain immunity. For instance, in disease such as small pox 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.
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.”
