Steady decline in Covid due to hybrid immunity but virus here to stay: Experts

Hybrid immunity has led to the steady decline of Covid in India but the virus is destined to stay long-term, becoming endemic rather than getting eliminated, say scientists as masks rapidly become a thing of yesterday and pandemic memories begin to fade.

Though Covid deaths have virtually ceased and case numbers are sliding, it would be a mistake to drop caution, they said, pointing to the impact of long Covid and the need to continue testing.

According to immunologist Satyajit Rath, the future trajectory of the Covid pandemic depends to a large extent on two questions: will new variants with unexpected characteristics arise, and how long will vaccine or infection-triggered immune protection last?

"While the outlook seems good, I think caution is advisable," Rath, professor emeritus at Indian Institute of Science Education and Research, Pune said.

Earlier this week, on Tuesday, India recorded its lowest single-day rise of 625 fresh COVID-19 cases since April 9, 2020 and reported no death in a 24-hour span, the first time since March 2020. On Friday, the health ministry reported 842 new coronavirus infections and six fatalities, including five reconciled by Kerala and one in Rajasthan.

It's a far cry from the summer of 2021. The daily number of cases in the country peaked at 4,14,188 (over 4.1 lakh) on May 7, 2021. The following month, on June 10, 2021, the number of deaths peaked at 6,148.

"It appears that the hybrid immunity that the Indian population enjoys is substantially protective," said Gautam Menon, professor, Departments of Physics and Biology, Ashoka University, who has been tracking Covid numbers in India since the start of the pandemic

Epidemiologist Ramanan Laxminarayan agreed.

He noted that Covid is waning due to a combination of vaccination and the fact that many people were already infected during 2020 and 2021.

"There seems to be sufficient cross-protection between vaccination, especially those who have received a booster, and the new strains so we should be protected for a while," Laxminarayan, director of the Washington-based One Health Trust, formerly known as the Center for Disease Dynamics, Economics & Policy said.

Many variants of concern have emerged for SARS-CoV-2, with the latest Omicron strain mutating into multiple sub variants.

Going forward, the scientists said Covid will most certainly become endemic in the country and not disappear altogether. A disease is called endemic when it is always present in a population but it spreads at predictable rates that can be managed by communities.

Menon added that Covid is destined to stay over the long term like influenza.

"There's a precedent for this - another coronavirus causes cold-like symptoms and has been around for some decades now," he explained, referring to the influenza virus.

Both COVID-19 and influenza (flu) are infectious respiratory diseases, and they share some similar symptoms.

"It is unlikely that Covid will disappear. It has already become endemic," Laxminaryan concurred.

"From current appearances and past experience, the most likely outcome will be endemicity rather than elimination I think," Rath said.

While there is a huge sense of relief, he also sounded a note of caution in gauging low case numbers and mortality.

"While it would be comforting to draw at least the conclusion that Covid-driven hospitalisations and deaths have now practically ceased, I am not sure that case testing is sufficiently systematically done even in hospitalised patients for such a conclusion to be dependable," he said.

"A forgotten point needs to be emphasised: we are not taking 'long Covid' illnesses into account. Yet it is well known that a substantial proportion of infected people develop prolonged illnesses of varying severity. It is a major error for us to be ignoring that," Rath added.

While India and many parts of the world are witnessing very low Covid numbers, new Omicron subvariants have led to an increase in cases in the US, China, Australia and Europe recently.

On Thursday, for instance, China recorded over 10,500 new Covid cases - the highest daily total since April when the country shut down its largest city Shanghai to combat a wave there. Similarly, the daily average cases in many states in the US have increased by 6 percent from two weeks ago.