Is COVID-19 now approaching an endemic stage? While the common interpretation of endemicity is ‘this is a disease we no longer have to be worried about’, what does it actually mean in epidemiological terms and what are the concerns for public health for the future? Will the infection spread at more predictable rates and will it perhaps become more manageable? In a conversation moderated by Ramya Kannan, Tarun Bhatnagar and K. Kolandaisamy discuss the science behind these questions. Edited excerpts:
Is COVID-19 on the path to becoming endemic?
Tarun Bhatnagar: As per the classical definition, a disease is endemic when it spreads in a limited area and at a rate which is relatively constant across time. In contrast, during a pandemic, the disease spreads to all the regions of the world and is present in some form or the other in all parts of the world with a relatively high rate of spread. We know that SARS-CoV-2 is still being detected in all parts of the world. In that sense, it is still a pandemic. However, we are seeing that in most or many parts of the world, the rate of spread is coming down, either naturally or with the interventions that have been put in place. So, yes, we probably could be moving towards endemicity. But that seems to be a little further away than where we are now.
K. Kolandaisamy: There are indications that the virus is moving towards endemicity. For example, in Tamil Nadu, we are seeing 200-300 cases, most of them from clusters. This is one indication that the disease might be moving towards endemicity. But we need to be very careful because even after two years, we are not very clear about the origin of this virus. There are three coronaviruses which manifest as common cold in human beings. Then, there was SARS-CoV-1 (2002), later called SARS [Severe Acute Respiratory Sydrome], and MERS [Middle East Respiratory Syndrome] (2012), all respiratory viruses. While SARS is not being monitored, tests are still being done for MERS. We are not very sure whether this virus will go the way of SARS, or take the path of MERS, or become like the three common cold viruses. This is a question only time can answer.
During the early part of the pandemic, COVID-19 was likened to the Spanish flu of about 100 years ago, but that flu did not turn endemic. Why do some diseases become endemic while others seem to vanish?
Tarun Bhatnagar: In order to understand the transmission of infectious diseases, we need to think of what is known as the epidemiological triad — the interaction between the agent, which is the organism that causes the disease, the host, which is the human body where the agent resides and spreads, and the environment in which both the agent and the host live and how conducive it is for the transmission of the agent.
The Spanish flu virus was not as transmissible as SARS-CoV-2. In fact, its reproduction rate was between 1 and 2. For SARS-CoV-2, it has gone up to 3, even 4, in some places. Second, we need to think in terms of the host, in order for the virus to spread. During the Spanish flu, it is understood that a bit, probably around a third, of the world’s population was affected and infected. It probably led to lower susceptibility, and herd immunity. Finally, the flu virus seemed to prefer a colder environment compared to SARS-CoV-2, which is probably agnostic to the environment, as we have seen.
K. Kolandaisamy: With the Spanish flu, the movement of soldiers, particularly in Europe, is said to have played a major role in the spread of the disease. Today, the movement of people has become quite phenomenal globally. This means that any disease can spread from anywhere to everywhere and human continuity will be there. Instead of disappearing like the Spanish flu, there is a greater possibility of SARS-CoV-2 moving to the endemic mode.
Can this move to endemicity within a short span of two years be attributed to a triumph of human efforts?
K. Kolandaisamy: Yes, the one important turning point in this case was the development of vaccines. That played a major role. Also, communication technology helped in disseminating information and awareness very quickly. And, as we now know, although some of the control measures were very harsh, travel restrictions and the initial lockdown measures also helped a lot.
It is to be noted that the fact that the pandemic spread very fast was a blessing in disguise: a large number of people were infected and this hastened the process of herd immunity.
Tarun Bhatnagar: I would distribute the credit equally between the virus and us, human beings. In the initial period, the virus spread so much that in a way it was a boon, in terms of people getting natural immunity to that particular strain of the virus. The vaccine has definitely been a game changer. I think it is historic to have a vaccine within such a short period of time, and completely incomparable to any other medical intervention that the world has seen. Even in terms of management of the disease, we learned a lot very fast.
What would be the link between cases and deaths in a possible endemic scenario?
Tarun Bhatnagar: If we look at different parts of the world, and India, we’re not seeing as many deaths or even hospitalisations. The cases are considerably low, even if they are showing an upward climb.
However, we are looking at another sub-lineage of Omicron, BA.4 and BA.5, initially reported from South Africa and now common in several countries. More recent reports from South Africa show a high number of excess deaths related to these sub-variants. Even Portugal, where the vaccination rates are pretty high, is reporting a high number of cases as well as hospitalisations. So, we will have to see how the virus is driving this — how good the virus is in terms of immune escape from natural immunity as well as from vaccine-induced immunity, how long does immunity persist, and the vaccine distribution in the population. These would be the three critical factors that would determine the future in terms of our interaction with the virus.
K. Kolandaisamy: We need to continue to be very careful in certain areas. We need to take care of people with co-morbid conditions and ensure that their health parameters are under control. For immunocompromised people, public health protocols such as wearing a mask, washing hands, and avoiding crowds are crucial. Besides this, we need to reach out to people who have not yet taken both shots and the booster dose and urge them to take the vaccines while explaining the risks of not being vaccinated. And we will need to continue to monitor [disease spread] and undertake surveillance of disease and morbidity in times to come.
What are the public health measures that governments will have to roll out in an endemic scenario versus a pandemic?
K. Kolandaisamy: Decades ago, our hospitals had separate wards for infectious diseases. Those were maintained by the local body. In those days, people with, say, smallpox, cholera, TB, chickenpox, acute diarrhoeal disease, etc. would be directed to these special wards or units in hospitals for treatment and, of course, would be segregated from others who were coming to the hospital too. However, over a period of time, with many public health successes — we have eliminated smallpox and there has been a huge decline in cholera cases and other infectious diseases such as chickenpox and measles — these units have been shut down, or are a shell of their former capacity. The system, therefore, had very little capacity to handle infectious diseases when COVID-19 began to spread. An exclusive facility to manage the cases with corresponding facilities for diagnostics and public health interventions is needed.
Tarun Bhatnagar: We are definitely not expecting the virus to disappear. It will probably continue to circulate at various levels in the population. So, the first thing that we need to be thinking of is setting realistic levels of what are the expected deaths or hospitalisations, vis-a-vis the infrastructure that is available. Ultimately, it’s about preventing deaths as much as possible.
The second is to set targets for reducing transmission. With more transmission, there is a risk of new mutations and variants emerging. So, we need to be looking at clusters or places where we see a higher rate of transmission. We need to set up routine testing facilities which are not camp-based and which are accessible and available to people.
With the emerging variants, again, the role of genomic surveillance becomes very critical — to be able to identify which is the circulating variant, its characteristics in terms of transmissibility, and ability to cause severe disease. Accordingly, public health interventions would have to be in place. Two things are really critical: to stop airborne transmission (by wearing masks, especially indoors and in crowded places) and ensure sufficient air ventilation in indoor spaces. I think that is an area in the realm of public health engineering, in terms of designing our indoor spaces and having good ventilation. That would be really important as we move forward in terms of preventing transmission of the virus.
Have there been some missed opportunities in the past couple of years, though much has indeed been done in this country especially in terms of adding to health infrastructure?
K. Kolandaisamy: We have missed the opportunity to effectively enforce segregation for infectious diseases in our hospitals. A number of pregnant women who got COVID-19 contracted the infection when they were in hospital for a check-up. They were not diseased, but caught the infection in hospital, where there is poor or little infection control or segregation practices. This is unacceptable.
Also, engineering buildings to ensure air flow and good ventilation, particularly in hospitals and public institutions, is very important. We also need to get people to get back to the discipline of following COVID-19 protocols. The National Medical Council can consider offering more specialisation courses in infectious diseases.
Tarun Bhatnagar: In terms of using data for decision-making, a positive that I see is that the pandemic brought together people who were working in their own silos — clinicians, mathematicians, epidemiologists, laboratory professionals, public health practitioners on the ground, anthropologists… So, we have an opportunity to now go further and change the culture of research. These kinds of collaborations help you get a bigger bang for the buck.
We’ve also developed systems to collect data, to transmit it, to analyse it and use it for various purposes at different levels. But there are opportunities to make that system more robust, more transparent and enable more efficient use of data. This can definitely go a long way in being prepared for the future and then tackling similar kinds of public health emergencies.
K. Kolandaisamy is a former director of public health in Tamil Nadu; Tarun Bhatnagar is an epidemiologist and senior scientist at the Indian Council of Medical Research-National Institute of Epidemiology in Chennai