What is the endemic stage of a pandemic?
People with Covid-19 will no longer legally need to be isolated in the United Kingdom and the tests are likely to be scaled back as part of a plan to live with Covid-19. California too has announced a shift to an endemic approach to Covid-19 that will focus on watching out for new variants and reacting quickly to outbreaks rather than issuing mandates for masking indoors.
A look at what an endemic stage of Covid-19 will look like, how the world will reach there, and what it will mean for control measures such as masking, social distancing in India and vaccination globally:
What does endemic stage mean, and are we there yet?
An infection becomes endemic when the rates become static in a given geographical location, meaning that the pathogen causing the disease — SARS-CoV-2 in this case — is likely to remain in circulation without causing large outbreaks as witnessed over the last two years.
Although the number of infections in India is consistently declining, experts say they cannot give a deadline on when the disease will become endemic. It will depend on the number of susceptible people in the population, vaccination rates, and emergence of new variants that are able to evade the immune response.
“Endemic means that the virus will continue circulating in the population and there will be periodic ups and downs when the conditions are favourable to the virus and less favourable to humans. Take, for example, flu which goes up in the winters and when the season is changing because of lower immunity in people or dengue which goes up after monsoons because of the availability of vectors. Covid-19 also may become seasonal and cause disease in the vulnerable,” said Dr Pramod Garg, director, Translational Health Science and Technology Institute (THSTI)-Faridabad.
An important determinant for whether we can “technically” say that the disease is endemic would be a representative sero-survey (population-level survey of antibodies against SARS-CoV-2) and laboratory susceptibility studies, said Dr Amit Singh, associate professor, Centre for Infectious Disease at the Indian Institute of Science-Bangalore.
“We can say that the disease is endemic only after we see that a majority of the people have immunity against the infection either through previous exposure or vaccination. If a representative sero-survey shows over 90% positivity, we can assume that. But we also need to see whether these antibodies can effectively protect against the current variants and a neutralisation study would tell us that,” Dr Singh said.
Does it mean we are safer?
A disease becoming endemic does not mean it is harmless. In an editorial in Nature, Oxford University professor on viral evolution Dr Aris Katzourakis argued, “A disease can be endemic and both widespread and deadly. Malaria killed more than 600,000 people in 2020. Ten million fell ill with tuberculosis that same year and 1.5 million died. Endemic certainly does not mean that evolution has somehow tamed a pathogen so that life simply returns to normal.”
He added, “Nor does it suggest guaranteed stability: there can still be disruptive waves from endemic infections, as seen with the US measles outbreak in 2019.”
Researchers are also wary of new variants emerging. Another Nature article on the virus’s future course said, “The sky-high circulation of the Delta variant and the rise of Omicron — aided by inequitable vaccine roll-outs to lower-income countries and minimal control measures in some wealthy countries such as the United States and the United Kingdom — offer fertile ground for SARS-CoV-2 to take additional surprising evolutionary leaps.”
How will control measures change if the disease becomes endemic?
Although experts have pushed for easing of restrictions, they say that there is a need to maintain high levels of testing and good genomic surveillance.
We need to maintain high levels of testing and ensure that the cases get reported. Testing is quite less in smaller cities and villages and with home testing becoming available even in bigger cities like Delhi, people are not reporting if they test positive. Testing can tell us whether infections are going up or down,” said Dr Singh. He also insisted on good genomic surveillance.
Talking about genomic surveillance when the disease becomes endemic, Dr Rakesh Mishra, former director of Centre For Cellular And Molecular Biology-Hyderabad which is one of the ten central labs of India’s genomic surveillance consortium, said, “It is not always about the numbers. During the peak of a wave, a lot of sequencing makes no sense. It is more important in a period of lull. That is the time to not relax.”
The best way to find new variants, he said, was to “One, conduct a general survey; sequence probably 1% or 2% of the positive cases. Two, wherever there are more cases from an area, we should sequence immediately. Third, we need to keep a very close eye on hospitalised cases. The sample of any person admitted to the hospital with positive Covid-19 should be certainly sequenced. If they needed to come to the hospital with severe symptoms, it may be because of a new variant.”
Should we continue to mask up?
“There is no real benefit in declaring that the disease is now endemic,” Dr Mishra said. “What is the hurry to remove restrictions? If we live with the new normal, we will be protecting the economy as well. We don’t know when a new variant might emerge. If we look at omicron, it did not cause severe disease in India but in the US it led to high rates of hospitalisations and deaths. The US is a smaller country, it is a richer country. We cannot afford to do what they did. We have all suffered, let us not fall into the ditch of a new variant,” he said.
Other experts agreed that the precautions should remain in place.
Another concern with officially declaring Covid-19 endemic would be fewer resources being made available for measures such as vaccination. “There is a vaccine inequity; not all countries are vaccinated. If the disease is declared endemic, then the 10% vaccination rate in some countries will remain 10%’ nobody will take care of that,” said Dr Singh.
“The more a virus replicates, the greater the chance that problematic variants will arise, most probably where spread is highest. The Alpha variant was first identified in the United Kingdom, Delta was first found in India and Omicron in southern Africa — all places where spread was rampant,” Dr Katzourakis wrote in the Nature editorial.
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