We are approaching a scenario that we all would have signed in April 2020, when hundreds of people died every day, but the endemic phase is still the worst end of the pandemic. The virus will continue to saturate the healthcare system from time to time and cause persistent COVID. With the exception of New Zealand, Governments appear to have given up on eliminating the virus. This has been achieved with diseases such as measles: in developed countries it is under control and there are only occasional outbreaks, in many cases caused by anti-vaccines, such as the one registered in Disneyland (California) in 2015, with more than a hundred cases.
The eradication it is even more complicated. As for human diseases, it has only been achieved with smallpox. It was in 1980, thanks to vaccination around the world since this virus lacks an animal reservoir.
On animals it was achieved with rinderpest. The who hopes to eradicate polio, the transmission of which is limited to Afghanistan and Pakistan. More utopian is the extinction of the pathogen, which has never been achieved, not even with smallpox, since there are two high-security laboratories, one in the United States and the other in Russia, which keep samples of this virus.
The famous American immunologist Anthony Fauci He recently said that COVID-19 should not be considered the flu, but measles, a disease controlled thanks to vaccination.
Possible endings of the pandemic
- 1 Endemic phase: continuous recurrence
The virus continues to circulate, albeit with minor incidences, and can cause seasonal peaks. Example: influenza and tuberculosis in certain areas.
- 2 Local elimination of disease
The disease is controlled in much of the world, but health authorities still monitor it. Example: measles.
- 3 Global eradication of the disease
The disease disappears all over the world. It has only been achieved with smallpox in humans and with rinderpest in animals.
- 4 Complete extinction of the pathogen
Distrust has prevented it from being achieved. Both Russia and the United States keep samples of the smallpox virus in separate laboratories.
Vaccines are the key again. As the doctor, researcher and professor at the University of Salamanca has said Miguel Marcos, “COVID-19 is only ‘like a cold’, after being vaccinated, but, curiously, many who compare COVID with the flu tend to minimize the importance of vaccines or directly be anti-vaccines.”
That is to say, “Endemic” is not synonymous with “harmless”. In this scenario, COVID-19 will continue to be a recurring concern, with possible seasonal outbreaks – such as influenza or respiratory syncytial virus – and unvaccinated and immunosuppressed people will continue to suffer serious illness or death, and without extensive vaccination coverage in other countries, vaccine-resistant variants may appear.
Why is it not possible to achieve the elimination of COVID-19 and it has been achieved with measles? The Americans Rustom Antia –biologist at Emory University in Atlanta– and Elizabeth Halloran –epidemiologist at U. Washington– have carried out a study in which they theorize about the endemic phase and its determining factors (Antia, R., Halloran, ME , “Transition to endemicity: Understanding COVID-19”, “Immunity”, 2021).
Among other factors, they explain that, while the measles generates sterilizing immunity for life – the disease is not suffered again after an infection or after being vaccinated – with coronaviruses, immunity declines over time, and it does so at different rates: the immunity that blocks the disease is reduced more quickly than that which reduces its severity. Thus, herd immunity is only temporary.
The researchers warn that the course of infection, the functioning of the immune system and the extent of the pathology are highly dependent on age: “Population demographics and the age at which people contract their first infection play an important role in determining the burden of disease ”, they emphasize.
In line with this idea is the possibility, pointed out by Ignacio López Goñi (University of Navarra), that contracting SARS-CoV-2 as children protect from the disease in adulthood, something that other specialists, such as Federico Martinón (U. de Santiago) question. Antia and Halloran mention the case of OC43, one of the four coronaviruses that today cause colds and that probably caused the epidemic of “Russian flu” in 1889 and 1890: it was severe in adults in the epidemic phase and then it subsided. What is not known is whether this was due to immunity acquired through childhood infections or to the biological evolution of the virus. Once again, the future holds many unknowns.