Finally, it seems we have turned a corner with the COVID-19 pandemic in the United States. More than 117 million individuals have been fully vaccinated. That’s about 35.4% of the population, with another 11% that have received at least one of the doses of mRNA vaccines. The U.S. Food and Drug Administration has authorized the Pfizer-BioNTech vaccine for children ages 12 to 15, meaning even more people will be eligible for vaccination and can help to further slow the spread of new cases. New infections, new hospitalizations, and deaths from COVID-19 have all been trending downward nationally over the past two weeks. Even epidemiologists are starting to feel some cautious optimism.
Globally, though, the world is still in a rough place. Cases and deaths have surged at various points in Brazil and India. Variants are still circulating, and we’re detecting new ones all the time. Global vaccination rates remain low, and access to vaccination in low- and middle-income countries is terrible. The Biden administration has called for a waiver of intellectual property rights so that developing countries can produce their own vaccines. It has also pledged to share doses of the AstraZeneca vaccine (not yet authorized in the United States), but donated doses don’t go very far, and starting production in other countries will take time to ramp up. In the meantime, the pandemic continues.
But 16 months into this, we can start looking to a future where the acute emergency of the outbreak has subsided. While most epidemics have a defined starting point, such as the first individual known to be infected or, in the case of SARS-CoV-2, the first report of an excess of cases of pneumonia with unknown cause in China, the end of a pandemic is generally fuzzier and more ill-defined. How will we know when this global disease outbreak is “over”? And what comes next?
Potential pandemic outcomes
René F. Najera, Dr.PH., epidemiologist and editor of the History of Vaccines Project from the College of Physicians of Philadelphia, explains that a large, immune population is what has typically ended other historical pandemics. “Either a substantial number of people got the disease and became immune, a substantial number died, or a successful vaccine was developed and successfully deployed,” Dr. Najera tells SELF. The 1918 influenza pandemic subsided because of the first scenario, but only after infecting approximately a third of the world’s population and killing at least 50 million people. Vaccines have worked to end the scourge of smallpox, while polio vaccines have reduced cases to fewer than 100 a year.
Now, once a pathogen becomes a pandemic, there are three possible trajectories it could take. Health officials could aim for elimination in a country or larger geographic area (the U.S. or North America), as we have done in the U.S. with measles, mumps, and rubella. Elimination means the virus is generally not present in the country but may be occasionally imported and cause local epidemics due to people traveling after being exposed during ongoing outbreaks in other areas of the globe.
A second possibility is that the pathogen could be eradicated, as was done for smallpox and is underway for polio: complete extermination of the organism from the wild on earth. This is very challenging and probably impossible for SARS-CoV-2, explains Dr. Najera, due to the zoonotic nature of the virus and its potential to jump species. “If it is found in other species, then it just goes from one to the other, hiding and returning as the conditions change.” Charles Kenny, Ph.D., senior fellow at the Center for Global Development and author of The Plague Cycle: The Unending War Between Humanity and Infectious Disease, agrees on the issue of eradication: “I’d be a bit surprised if we managed it with SARS-Cov-2, which we’ve found in cats, dogs, mink, gorillas, and tigers, for example, and which may have originated in bats.”
Additionally, we are uncertain about whether the COVID-19 vaccines in use will provide long-lasting immunity, as the smallpox and polio vaccines do. If not, that could leave individuals unprotected as their vaccine immunity wanes. Furthermore, to attempt eradication, the vaccine must be available to all, which is not feasible right now, though manufacturing is expected to ramp up in the rest of 2021 and 2022. Asymptomatic cases of infection would also stymie an eradication campaign, as they have for polio, allowing for undetected spread. Having very distinct symptoms, as with the smallpox rash, made it easier to identify cases and control smallpox transmission during the eradication campaign.
So eradication is out, and elimination would be very difficult, at least at this point in time. That leaves us with the third possibility: an endemic virus. This means it will be present at a low level in the population for the foreseeable future. Dr. Najera suggests that SARS-CoV-2 will become more similar to the four endemic human coronaviruses that generally cause colds: “another nuisance virus for some and severe enough to kill for others.” However, with a considerable portion of the population vaccinated, we’ll see far fewer infections and deaths than we’ve experienced over the past 16 months, and even when outbreaks occur, they will be less likely to overwhelm hospitals.
This endemic conclusion is consistent with the outcome of the 2009 H1N1 “swine flu” pandemic. On August 10, 2010, approximately 16 months after it first began, the World Health Organization (WHO) declared the pandemic “over” but cautioned: “As we enter the post-pandemic period, this does not mean that the H1N1 virus has gone away. Based on experience with past pandemics, we expect the H1N1 virus to take on the behavior of a seasonal influenza virus and continue to circulate for some years to come.” This has come true. More than a decade later, descendants of the 2009 pandemic virus are still circulating, as pandemic influenza viruses did after the 1918, 1957, and 1968 influenza pandemics. At some point, the WHO will issue a similar declaration for COVID-19, when levels of new cases are sufficiently low in most countries around the world. But this will not be the end of the virus.
The next phase of pandemic life
Monica Green, Ph.D., historian of medicine and global health and independent scholar, points out that a pandemic “ending” is really in the eye of the beholder; pandemics last longer than just the acute and most deadly outbreaks. “Most history of medicine focuses on epidemics: the visible part of outbreaks in human communities,” she says. “And most human communities have always only been able to see things at small scales. So ‘epidemics’ end when a disease is no longer visible to us,” however “us” is defined, from city to nation-state. Dr. Green’s own work studying the spread of Yersinia pestis, the bacterium that causes bubonic plague, the agent of the Black Death, shows that past pandemics technically lasted hundreds of years or more. But that doesn’t mean those outbreaks were at their most severe the entire time—different phases were involved.
So, although we don’t seem to be out of the woods yet, we are likely heading for the start of the post-pandemic phase of the outbreak in the U.S. New variants may still pop up, and transmission is expected to flare occasionally, especially in areas that have low vaccination rates.
It’s important to note that the reduction in cases in the U.S. will not automatically mean the end of the pandemic, which is by definition global. Depending on the speed of worldwide vaccine distribution, the pandemic could linger for another year or more in low-income countries. Dr. Kenny hopes that vaccines will “crush any future waves” in the U.S., but there is a very real fear for many low- and middle-income countries “that the waves will keep coming unless we do a far better and far faster job of scaling up global production and distribution of those vaccines.” Currently, there are proposed partnerships to increase vaccine distribution and production in these countries, and additional vaccines are still being tested that could be used in countries that are still experiencing high levels of COVID-19 infections.
Even with effective vaccines, the end of the pandemic is not predetermined. Other vaccine-preventable diseases can give us a glimpse at the probable future of SARS-CoV-2, a virus that is tamed by vaccination but is not gone and may remain at high levels or routinely escalate in areas where vaccination rates are low, in the U.S. and around the world. “While we see flare-ups around communities that are vaccine-hesitant, we don't really see measles at its full potential anymore,” notes Dr. Najera. This is a scenario that could be replicated with SARS-CoV-2. Overwhelmed hospitals will be unheard-of in vaccinated populations, but like measles, COVID-19 could remain a serious issue in countries where vaccines are scarce or difficult to supply or distribute to those who were never vaccinated (for example, children born after the first vaccination campaigns).
Lessons learned
Once the pandemic ends, will the general population continue to think about it? The 1918 influenza pandemic is famously called the “forgotten pandemic,” without national monuments to memorialize the dead and recall their struggles and sacrifices, like those that exist for wars and many natural disasters. Post-pandemic, says Dr. Kenny, “as a rule, things go back to normal pretty fast.” But Dr. Green says that the specter of “long COVID” may keep the pandemic more visible in the public eye and collective conscience: “I think there will be a greater sobriety about what failure to control viral infections means.”
As cases diminish in wealthy countries, we are also thinking about lessons learned from the failures of pandemic response as we prepare for the next “big one.” Dr. Najera points out that misinformation can spread faster than the virus did. “We have not yet learned how to use the internet effectively to channel more information than disinformation,” which laid the groundwork for the virus to spread more freely than it might have if communication had been better from the start.
Dr. Kenny says that as far as mortality from the virus went, SARS-CoV-2 had a relatively low death rate. “But it has had the largest immediate global economic impact of any pandemic in history,” he says. “Estimates of the global cost of COVID-19 and responses range upwards of $10 trillion—compare that to total global output of perhaps $5 trillion around the time of the 1918 flu pandemic.” He explains that the interconnected global economy exacerbated the impact of stay-at-home orders and travel restrictions. “That’s one more reason why it is so important that next time we act far faster as a global community to shut down an outbreak before it becomes a pandemic.” He fears that if things get back to normal too quickly, we may be setting ourselves up for failure in the long run; if we “forget the lessons, we don’t strengthen global cooperation against pandemics and make sure we have built up contact tracing capacity.”
Dr. Green adds, “I have always felt that the emphasis on mortality as the measure of an epidemic/pandemic disease's importance was misplaced.” She notes it is difficult to compare COVID-19 mortality directly to past epidemics: “This disease clearly would have been more lethal if it had struck before modern clinical interventions (oxygen therapy, respirators) were available.” Still, she cautions, “We have seen what a relatively low-mortality event looks like in real life. This is not a computer simulation or a movie. We have been devastated in ways we will only be learning about in the coming months and years. I hope we pay attention.”
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