More than a year after the World Health Organization (WHO) declared the COVID-19 pandemic's onset, we are now looking to reduce the spread of the virus rather than eliminate it entirely. With the introduction of several effective vaccines and the implementation of safety measures such as travel bans and quarantine, we are starting to see a decrease in COVID-19 cases in some parts of the world. According to a survey conducted by Science Alert, which included eight experts in epidemiology, 75% of them responded that COVID-19 will become endemic, raising doubts about the possibility of eradicating it in the future and whether it will remain endemic in certain regions.
What does it mean for the virus to be endemic?
This means that there will always be infected individuals transmitting the virus to others, who then recover. Over time, each infected person, on average, infects another person, keeping the number of cases approximately constant, says Professor Graham Medley, an expert in disease modeling from the London School of Hygiene and Tropical Medicine. This is in stark contrast to the high level of transmission witnessed during the pandemic. Many common diseases are endemic, including coronaviruses that cause colds. Professor Medley stated, "Endemic infections typically affect children and cause mild symptoms. Endemic coronaviruses are not associated with severe disease. By the time children reach adulthood, they will have been infected, and may get infected multiple times, thus they are immune."
How have past epidemics ended?
Disease modeling and epidemiology expert Professor James Wood from the University of New South Wales (UNSW) in Sydney noted, "When the pH1N1 2009 virus (swine flu) emerged in 2009, it became epidemic within a year of the initial pandemic, driving the existing H1N1 influenza strain in humans to extinction." Many viruses responsible for past epidemics, including the 1918 influenza pandemic, continue to circulate today. Eradicating a disease is not easy. To date, the WHO has only declared two diseases completely eradicated worldwide: smallpox and rinderpest. Both required large global vaccination campaigns to achieve herd immunity.
Can we eradicate COVID-19 using new vaccines?
Smallpox and rinderpest were eradicated using vaccines; now that multiple COVID-19 vaccines are available, can we use them to eliminate this disease? Dr. Lee Riley from the University of California, Berkeley, highlights a key obstacle to eradicating COVID-19: the responsible virus can mutate to become resistant to vaccines. He said, "In places with a mixture of vaccinated and unvaccinated populations, vaccines may exert selective pressure on the virus to undergo further mutations, and these variants will spread among unvaccinated individuals. Some variants may also infect vaccinated individuals." He added that another difficulty in achieving herd immunity is that some currently available vaccines do not provide 100% immunity against COVID-19.
Epidemiology expert Professor Jane Heffernan from York University contends that "COVID-19 infection and vaccination can stimulate high levels of protective immunity in individuals. Acquired immunity can protect against infection, or, in the case of infection, reduce the severity of the disease." There is also the challenge of vaccinating many people in numerous countries. Professor Wood from UNSW emphasized that "the constraints on our capacity to produce vaccines, estimated at 15-20 million doses per day, mean that achieving high global coverage for two doses will take over a year, even with relatively fair vaccine supply." Dr. David Heymann from Massey University added that "there is a huge disparity in vaccine distribution, with only a small fraction of the world's population currently vaccinated. This means that unless this issue is resolved, the virus is likely to become endemic in those countries."
Despite these challenges, it is still theoretically possible to vaccinate enough of the world’s population to achieve herd immunity and eradicate COVID-19. Interestingly, Professor Wood noted that "eradication and elimination may not remain priorities if the remaining protection from the vaccines against severe disease remains strong," stating, "If we can protect people from experiencing severe symptoms from COVID-19, there may be no incentive to eradicate it entirely."
