Dr Vidya Jha | Associate Professor & Consultant (In-Charge), Cytogenetics lab, Assistant Medical Administrator Amrita Institute of Medical Sciences, Kochi
The Centers for Disease Control and Prevention (CDC) defines endemic as the constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area. This observed baseline or the endemic level of the disease is not necessarily the desired level, which may in fact be zero. The disease may continue to occur at this level indefinitely, in case of lack of any intervention and assuming that the disease level is not high enough to exhaust the entire pool of susceptible persons. Therefore, this baseline level is often regarded as the expected level of the disease in the population.
Because of the difference in timing of achieving herd immunity in various populations and nations and the uncertainty in duration of protection from COVID-19 vaccines, it is likely that some measures such as booster vaccines might be required indefinitely. SARS-CoV-2 will continue to exist. Even when a country reaches herd immunity, ongoing surveillance, booster vaccines, and potentially other measures may be required. As of now, Delta variant has effectively shifted the overall herd immunity out of reach in most countries at least in the short term.
So far, India has not been able to achieve herd immunity and a more realistic epidemiological endpoint appears to be when COVID-19 can be managed as an endemic disease. However, the biggest overall challenge is the emergence of a significant new variant that is more transmissible, more likely to cause hospitalisations and deaths, and or more capable of infecting vaccinated people. The existing vaccines have not been able to prevent infection from the Delta variant. Also, serial blood tests suggest that immunity may wane relatively fast. This has prompted some developed countries to start offering booster doses to high-risk populations or planning for their rollout.
Therefore, many countries including India would like to reach a stage of endemic COVID-19. But India remains as an at risk country for significant waves of the disease. The overall immunity is low, owing to the fact that large part of the Indian population is not yet fully vaccinated. The possible time frame for India to manage COVID-19 as an endemic disease is also less clear. There has to be a shift in focus of public-health efforts from managing COVID-19 case counts to managing severe diseases and deaths when the Delta driven wave of cases decline.
The challenges in reaching endemicity as the endpoint continue to be the emergence of new variants that evade vaccine-mediated immunity. They frequently cause severe disease in the vaccinated persons and are highly transmissible, waning of natural and vaccine-mediated immunity over time, rolling out vaccine booster doses quickly enough to maintain immunity and defining an acceptable burden of disease (for example, setting different targets for disease burden in vaccinated and unvaccinated populations). The biggest task will be determining what burden of disease is low enough to warrant lifting of public-health restrictions.
However, with time, against all odds, we will be better protected against hospitalisation and mortality due to COVID-19 owing to more vaccination coverage, natural immunity from prior infection, booster doses, full approval of vaccines in India and authorisation of vaccines for children.
