Explained | What is ‘immunity debt’, and is it caused by coronavirus lockdowns?
Home Health Explained | What is ‘immunity debt’, and is it caused by coronavirus lockdowns?
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Explained | What is ‘immunity debt’, and is it caused by coronavirus lockdowns?

Amid a gradual easing of lockdowns, why are some countries reporting a higher number of respiratory infections?

The story so far: As countries start lifting curbs imposed on societies due to the COVID-19 pandemic, news reports have indicated higher rates of respiratory infections, even unseasonal diseases such as influenza and the respiratory syncytial virus (RSV). Doctors have called this the “immunity debt” brought on by non-pharmaceutical interventions (NPIs) put in place to reduce the spread of the SARS-CoV-2 virus.

What is ‘immunity debt’?

The NPIs, including social distancing, use of masks, and hand hygiene, were seen as being effective in breaking the chain of transmission of the SARS-CoV-2. During the pandemic, they have been employed to do exactly that, and have succeeded at varying levels in countries, depending on the level of compliance.

However, they have had unintended consequences for other respiratory infections as well. Rachel E. Baker et al have highlighted the issue in a Proceedings of the National Academy of Sciences of the United States of America (PNAS) paper titled The impact of COVID-19 nonpharmaceutical interventions on the future dynamics of endemic infections. America is among the nations seeing an increase in the number of RSV cases in the infant population. “Non-pharmaceutical interventions (NPIs) have been employed to reduce the transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), yet these measures are already having similar effects on other directly transmitted, endemic diseases. Disruptions to the seasonal transmission patterns of these diseases may have consequences for the timing and severity of future outbreaks,” it states.

Gagandeep Kang, Professor of Microbiology, Christian Medical College, Vellore, explains: “Basically, when you are constantly exposed to infectious agents, what you are doing is boosting the immune response in the human body. If you don’t see the bugs you normally see, there is a possibility that there are unseasonal outbreaks, and with greater severity than usual.”

Q. Sue Huang, Tim Wood and others record in Nature Communications that New Zealand, which has seen a number of RSV cases, has a well-established influenza circulation pattern with peak incidences in the winter months. “Remarkably, influenza virus circulation was almost non-existent during the 2020 winter, a 99.9% reduction compared with previous years,” the report said. They postulated that the country’s use of stringent lockdowns and border controls had resulted in substantial reduction in contact between individuals, leading to the fall in the number of cases in 2020.

Is the impact only on respiratory viruses or on other viruses as well?

RSV can be severe in very young infants, but it is commonly a winter infection. Babies gain some protection from mothers, but the mother must have had some exposure to the virus. If mothers are not exposed, it leaves the baby unprotected, and if it is not very severe, children can be supported through the infection, explains Dr. Kang. A monoclonal antibody is used to treat RSV. In adults, an outbreak of seasonal influenza is expected.

While lockdowns, as they reduce the chances of transmission, might affect other respiratory infections, is it possible that there might be a rash of other infections as well, for instance, gastrointestinal (GI) infections? Ashish Bavdekar, a Pune-based paediatric gastroenterologist, says this may be possible, although data to support it is not available in India. “We do not have very good data on this. In fact, we don’t have data on the number of cases of RSV too, but we will know about GI-related infections in a few months,” he says. “This is such an unusual phenomenon that has occurred. But I don’t think the change of season will have long-term epidemiological effects, they will go back to the regular seasonal impact in a while.”

Should there be a rethink on lockdowns?

Despite the huge social and economic costs, lockdowns and social distancing have shown demonstrable success in containing the pandemic. But how stringent should lockdown measures be in future?

The Nature Communications article calls for a reassessment of the role of NPIs and an analysis to identify the most effective components to prevent respiratory virus transmission and infection. This might yield “new and sustainable interventions that can minimise and prevent seasonal and epidemic respiratory viral illnesses in the future”.

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