Experts analyze possible outcomes of the pandemic: from eradicating the virus to cohabitation, and even losing control of transmission.
Amado HerreroMar
In the second year of the pandemic, two opposing trends are shaping the evolution of COVID-19: on the one hand, in many countries, the progress of vaccination is increasing the number of immunized individuals, gradually bringing us closer to a return to normalcy; on the other hand, the spread of the Delta variant and vaccine hesitancy among some sectors of the population are complicating efforts to reduce infections. These multiple factors are converging and creating uncertainty about the future. To explore the possible outcomes, a group of researchers has analyzed, in an article for the journal JAMA , the probability of four scenarios: eradication, elimination, cohabitation, or loss of control over infections.
According to the authors—and most scientists— eradication of the virus is unlikely . Reducing SARS-CoV-2 circulation globally to zero would require that “both vaccine-derived and infection-derived immunity be highly effective, long-lasting, capable of preventing secondary transmission and reinfection, and protecting against all types of present and future viral variants.”
Furthermore, the authors explain that the risk of it jumping between different animal species complicates its eradication, as it can survive in populations of bats, mink, or other animals. In January, the journal Nature conducted a survey of more than 100 immunologists, infectious disease specialists, and virologists to gauge their opinions on the future of the novel coronavirus.
Nearly 90% of those surveyed stated that the virus will become endemic , meaning it will continue to circulate in pockets of the world's population for years. "If eradication is not possible, COVID-19 will become an endemic disease," agrees Eli Adashi , a researcher and dean emeritus at Brown University in the United States. Given the current circumstances, Adashi adds that "cohabitation is the most likely scenario," although the number of virus-free regions may grow as access to vaccines expands worldwide and doubts about them dissipate.
Seasonal virus
As global immunity from exposure or vaccination becomes widespread, the symptoms of the disease experienced may begin to resemble those of the common cold, caused by other seasonal viruses. “An endemic state can occur once most people are no longer immunologically naive—that is, once they have been vaccinated or infected at least once,” explains Jennie Lavine , a biologist at Emory University and author of a Science article on the evolution of the pandemic. “Then, when they are exposed and infected again in the future, they will likely be protected from severe forms of the disease.”
Once most of the population has had initial exposure to the virus, the rate of transmission should slow, but it may not drop to zero. “As immunity wanes and seasonal transmission rates increase next fall (at least in northern climates), we are likely to see another wave of infections,” Lavine warns. “Those who are not yet protected from the disease by vaccination (or primary infection) will still be at risk, but if we can vaccinate most people, a new wave of infections should not mean a large wave of severe illness.”
Worst-case scenarios
More worrying are other scenarios considered by specialists, especially what they call a "conflagration ," a stable state characterized by a continuous presence of SARS-CoV-2, even if moderate. This is a more likely scenario where large segments of the population remain unvaccinated, either due to lack of access or reluctance.
“The virus would have continuous opportunities to replicate and adapt to evade both natural and vaccine-derived immune responses,” the authors warn. “Among vaccinated populations, infections could continue to emerge periodically due to incomplete vaccine-derived immunity, waning efficacy, or evasion mechanisms by new viral variants.”
The extent of the outbreak could depend on vaccine efficacy and uptake across different regions. Potential gaps in coverage have been observed for specific variants of certain vaccines. For example, a recent study in the United States, using data from 75,000 patients, indicated that the protection provided by the Moderna vaccine may be longer-lasting than that provided by Pfizer.
In any case, the authors emphasize that the future of the epidemic will depend as much on the collective decisions of the international community as on local realities . Countries like Israel, New Zealand, and Vietnam appear to be heading toward elimination; however, the United Kingdom, the United States, and China have adapted to a state of coexistence, while India and other Southeast Asian countries, along with much of South America, are immersed in a state of conflagration. “To reverse the fate of nations in a state of conflagration, it will be necessary to increase population immunity through vaccines capable of neutralizing new viral variants,” the authors of the article in JAMA warn.