It seems a little silly to look at the precise definition of the word ‘pandemic’ after a year and a half of having been in the middle of one, but for context, let’s just do this: a pandemic is a disease prevalent over a whole country or the world. Endemic refers to the constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area. Recently experts have started to use the term ‘endemic’ for the COVID 19 pandemic. How scared should we be?
As you can see from the image above, there are many diseases that live within populations, with sporadic outbreaks every now and again. So for instance, a disease such as smallpox was around for many decades until it was finally eradicated – which is why older generations have the characteristic mark of the smallpox vaccine while younger generations do not. After very intensive vaccine campaigns over many years, we also managed to eradicate polio. However, we do still often see people with disabilities caused by the disease because it was around till not too long ago.
Now we hear about dengue, chikungunya outbreaks practically every year, with public service messages from the government telling us how to stop the spread. Several types of the flu are also endemic; so that in many developed countries, the flu shot is taken as a matter of course at certain times of the year. We still have the scourge of leprosy; so much that sufferers are still ostracised by society; and leper colonies are still a social reality of ours.
Infections that are prevalent only in humans – such as smallpox and polio are possible to eradicate. However, pathogens that are also found in animals aren't possible to eradicate. This is why vector-borne diseases such as malaria, dengue, Japanese encephalitis (spread by mosquitoes) have been around for so long and still are around. These infections spurt at certain times of the year when mosquito populations rise. This is also why bird flu and swine flu seem to go away and then come back.
The immunity of a population to a certain pathogen is not constant. It can wane over time. Outbreaks occur when immunity to a pathogen found among animals such as bats or camels or cats wanes in the general population. Now many experts say that in the case of this coronavirus, it will continue to circulate within populations and will keep infecting people who have no immunity (which is a result of exposure or vaccination).
This view seems to predict that we will have to learn to live with this virus and that we will experience outbreaks now and then. The important difference here is that we may see ‘symptomatic infection’ but not ‘disease’. My understanding of an infection is when there is an attack by a pathogen on the body and the body responds with fever, pain and such symptoms which are the body’s own defence mechanisms. The disease stage is when the pathogens weaken the body’s immune system and cause damage to the cells of the body.
Serological surveys of Indian populations have indicated at about two-thirds of the population now has antibodies to this virus. This means that this proportion of the population likely had the infection (in many cases asymptomatic) but not the disease. Hence, a significant proportion of the population may now be protected.
So, what now? Doctors tell us not to think in terms of pandemic and endemic and to concentrate on getting vaccinated and on stopping the transmission of the virus. Many of us may have antibodies, but we still don’t know how the virus will mutate and what new form it will take. The virulence and the transmissibility of new variants may be less – but is as likely to be more. Right now it seems as though the SARS-CoV-2 virus is going to continue to be around and we cannot afford to let our guard down.
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