Has COVID-19 turned into another winter bug? Lessons to learn from JN.1 spread

With three waves clustered between December and March, experts analyse what this means for severity of infection.

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SARS-CoV-2 is transforming into a winter bug. (Express photo)

There was a time when 42-year-old Renuka Ghosh looked forward to mountain hikes and a celebration of her birthday, which coincided with Christmas on December 25. However, the pandemic has rewritten the winter narrative for her as she falls sick routinely at this time of the year. Now, three bouts later, she masks up outdoors and isolates indoors most of the time.

Yet, despite Renuka’s efforts, there’s a challenge she can’t escape: SARS-CoV-2 is transforming into a winter bug. Its presence looms large, becoming most prominent during the colder months, mirroring the seasonal patterns of the flu and other lesser-known viruses like respiratory syncytial virus (RSV), rhinovirus, and adenovirus. “Covid is here to stay as a winter bug,” says Dr Rahul Pandit, Chair, Intensive Care Unit, at HN Reliance Hospital and former member of the state Covid task force.

Why does Covid intensify in winter?

“Scientific studies say that colder temperatures and drier air create an environment conducive to the stability and transmission of respiratory viruses, potentially contributing to the heightened impact of COVID-19 during the winter months,” says Dr Lancelot Pinto, senior pulmonologist and epidemiologist at Hinduja Hospital. This helps them mutate. Aerosolised particles from a COVID-19 positive person’s cough lingers in the air longer, putting healthy people at risk.

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However, COVID-19’s unique characteristics, such as its longer incubation period and ability to spread asymptomatically, contribute to its distinct impact on winter health dynamics, according to Dr Subhash Salunkhe, the former chairman of the Covid-19 task force. In fact, a 2020 study had shown that even a one per cent decrease in humidity could lead to a significant six per cent increase in the number of COVID-19 cases. This is borne out by the fact that in India, both the second (2021) and the third waves (2022) happened between December and March, when temperatures across the country were lower. The JN.1 sub-variant of Omicron is also spreading now.

Additionally, seasonal factors affecting human immune responses can drive the virus to adapt. These mutations can lead to the emergence of new variants, influencing the virus’s behaviour and potentially impacting its transmissibility and severity of illness during the winter months. JN.1, when compared to its parent BA.2.86 lineage, has an extra spike mutation, L455S, notably amplifying its immune evasion capabilities. Variants like HK.3 also have immune escape capabilities compared to the EG.5.1 variant.

Will variants be more virulent?

As immunity develops through infection or vaccination, the severity of illness typically diminishes over time. Most respiratory viruses entail initial severe outbreaks followed by milder infections due to immune memory. “While the emergence of variants is a concern, it doesn’t necessarily indicate heightened lethality, reflecting a common feature in the evolution of viruses,” says Dr Salunkhe.

Will those who had the infection before become more vulnerable to seasonal attacks? What about those who are battling long COVID?

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As it transforms into a winter bug, COVID-19 will persist as a risk for those with compromised health conditions and comorbidities. Dr Pradeep Awate, the former surveillance officer of Maharashtra, in fact, calls for research on long COVID vulnerabilities in our own population. “This is crucial as the majority of existing studies are derived from Europe and the US,” he says. We also have to see if, as Dr Pandit says, COVID has a lasting impact beyond winter.