As the world approaches the one-and-a-half-year mark of Covid-19 pandemic, people across the globe are wondering how and when this invisible war at the microscopic level will come to a conclusion! Experts opine, there might have been a short-lived opportunity to halt the spread of SARS-Cov-2 virus that causes Covid-19 disease at the earliest stage, similar to what happened in case of SARS-Cov-1 pandemic during 2002-03. But that did not occur apparently due to procrastination and complacency displayed by earliest affected countries. Vaccinations now appear to be the only course out of this malady, but that is a very expensive route and the short-term prospects for mass inoculations are indeed bleak for most countries of the globe. However, amid all this gloom, one truth stands out from history - the pandemics always end, and vaccines have never played any significant role in making those recede.
Let us retrace history. When the Spanish Flu Pandemic caused by H1N1 virus hounded the planet during 1918-19 causing 500 million deaths worldwide, there were no flu vaccines. Later on, flu vaccine was used mostly by the military when the Asian Flu Pandemic caused by H2N2 virus killed over 1 million people globally during 1957-58. After that, when the Hong Kong Flu Pandemic caused by H3N2 virus swept the world and killed another 1 million during 1968-69, the USA rolled out about 22 million doses of the vaccine; but the pandemic as well as the demand for vaccines had subsided by then. There was a repetition of this phenomenon when the H1N1 Swine Flu Pandemic struck in 2009-10 causing 575 thousand deaths worldwide. Although the world had the capacity then to produce millions of doses of H1N1 vaccines, most of the vaccine orders had to be cancelled as they were not needed.
Now, one can ask, how did those pandemics peter out? The viruses certainly did not go away, as evident from the continued existence of modern variants of the Spanish Flu virus H1N1 as well as the subsequent H3N2. Mankind also did not develop any herd immunity against them, an immunity level that protects a population after getting infected or vaccinated on a massive scale (70% to 90%). Rather, the pandemic-causing viruses and the humans themselves underwent transformation. Through this process, the human immune system learnt enough to prevent the infections most of the time. In this way, the people and viruses reached a state of immunological accommodation, whereby the viruses can trigger small surges of milder ailments instead of causing devastating sicknesses. As a consequence, the pandemic flu became a seasonal occurrence and the viruses turned into endemic entities. If this trend continues, then the SARS-Cov-2 can also be expected to join other coronaviruses that cause colds among humans mainly during winter, when conditions favour their transmission.
But the big question is: when is that likely to happen? A leading WHO epidemiologist Maria Van Kerkhove recently admitted she was expecting the current acute phase to be over by now, which could have materialised if steps taken by countries like New Zealand were replicated by others for bringing virus transmission under control. But experiences from the four previous pandemics suggest that viruses usually morph from pandemic pathogens to endemic ones within one and a half to two years of their first appearance. However, the four pandemics discussed earlier were caused by flu viruses, and consequently a different pathogen like the novel coronavirus or SARS-Cov-2 may follow a differing time-line before receding.
As the era of modern virology is quite recent, there is no historical record about the severity of illnesses the previous four human coronaviruses (prior to SARS-Cov-1, MERS-Cov and SARS-Cov-2) had caused when they started infecting humans via other animals. Or, on how long a time they took for settling down into an endemic state. Consequently, the flu pandemics are the closest analogy one has for drawing a future roadmap. The durations of those pandemics indicate that a timeline of 2 years or less has consistently remained the best-fit in all cases.
A biologist at Emory University of USA named Jennie Lavine and her co-authors predict that as older adults acquire experience of coping with the novel coronavirus, it will no longer induce severe disease among a majority of them. That training of the immune system will probably make future Covid-19 infections equivalent to common cold. As the degree of protection among adults attains a safe standard over time, the children will be mostly infected by Covid-19. And till now, these infections are rarely serious among kids, which is the general pattern of human coronavirus infections. All humans develop some form of immunity from natural infection or vaccination, which implies they do not get very sick when they are infected again, ultimately resulting in virus transition to an endemic phase.
And Lavine claims, "It's not a death sentence in any way, shape, or form to say we're not going to have herd immunity. It just means it's going to become endemic and then the question is, is it going to be mild and endemic, or is it going to be severe and endemic? And I would say, my odds are on mild and endemic at some point. I think, that seems really, really likely." (Helen Branswell, STAT, 19 May 2021). Endemic SARS-Cov-2 is likely to follow a seasonal pattern, spreading mainly in the winter months when people spend more time indoors in close proximity with each other. Some of the seasons may be more severe than others in the early stage, but not pandemic severe.
In any case, the pragmatists argue that countries should not wait for the vaccines or for the virus to morph into an endemic state. Rather, people should continue using tools like masking and social distancing that contribute to stopping the transmission. The communities can reach very high levels of disease control in this way, and the pandemic then ceases to cause mayhems in societies across the globe.
Dr Helal Uddin Ahmed is a retired Additional Secretary and former Editor of Bangladesh Quarterly. [email protected]