Now that we’re at the two-year mark with the pandemic, things are starting to feel a lot better. “Normal,” even. So, does that mean it’s “endemic”? And what does that actually mean? “When a disease goes from acute to endemic it essentially means that the virus will not be eliminated (like in the case of smallpox) but will circulate in populations throughout the year,” says Dr. Jennifer Haythe, MD, Associate Professor of Medicine and Co-director of Columbia Women’s Heart Center. “However, in theory, the virus will become milder as enough people will have developed some immunity either through infection or vaccination. Hospitalizations and deaths would theoretically decline and an endemic virus would circulate similar to cold and flu viruses.” In other words, COVID entering an endemic phase means it will continue to exist, but it will become more manageable.
What factors affect the transition of an acute disease to an endemic one?
An important factor is the level of immunity in the community. “When there are high levels of protective immunity within a community from vaccination and from natural disease, transmission rates go down. In the case of SARS-CoV-2, from what we have seen, so far anyway, protection from vaccination and natural disease wanes over time,” Dr. Erica Johnson, MD, Chair of the Infectious Disease Board at the American Board of Internal Medicine, explains. “So, a successful transition will involve keeping this level of community immunity high so there is a manageable level of disease transmission.” But another important factor is more of a collective societal decision. “It’s a change in how we balance what risks we are willing to accept with what activities and behaviors we want to resume,” says Dr. Johnson. “And also how we learn to live with the need to have reasonable protections in place to mitigate the risk of transmission when we start to see more disease circulating in the community.”
What’s a likely timeline for COVID-19 to become endemic?
No one knows for sure. There are some that speculate that the SARS-CoV-2 Omicron variant is so transmissible and has caused so many new infections that this boost in natural immunity combined with high rates of vaccination in some places may help with this transition, Dr. Johnson explains. But there are still many communities in the US and many countries around the world where vaccination rates are not nearly high enough. And since immunity from natural disease wanes over time, there is still the possibility that a new variant that is even more transmissible than the Omicron variant could arise and replace the Omicron variant. It is also possible that this hypothetical variant could have the potential to evade existing immunity, Dr. Johnson adds. Unfortunately, there isn’t a precedent for this kind of scenario with any of the pandemics leading up to COVID-19. “It’s truly the first global pandemic in human history to take hold in the era of rapid international air travel and efficient ground transport, and with a world population approaching 8 billion people increasingly crammed into crowded urban centers with significant person-to-person contact,” says Dr. J. Wes Ulm, MD, PhD, physician and medical researcher. “Previous major epidemics and pandemics have simply burnt themselves out, largely by just running out of hosts and being sealed off due to the relative isolation of communities that’s prevailed through most of recorded history—which is what happened with the prior SARS and MERS epidemics (caused by coronaviruses roughly similar to SARS-CoV-2) earlier in the 21st century.” At the time of the last large-scale worldwide pandemic, that of the Spanish flu in 1918-1920, global population was less than two billion, and commercial air travel—particularly across international borders—had yet to take shape in any significant way. “This type of isolation resulted in the subsiding of contagion and eventual fizzling out of the pandemic,” Dr. Wes explains. “Now, we have something of a perfect storm for contagion with a coronavirus capable of both droplet-borne and airborne spread, a capacity for more mutations and immune evasion (as we’ve seen with the Delta and Omicron variants) and billions of human hosts who can rapidly travel and intermix worldwide.” While the timeline is hard to estimate, “if the virus continues to mutate into versions that cause milder disease (like Omicron) then we could be headed there more quickly,” says Dr. Haythe.
What can the history of deadly viruses teach us?
Whether we consider the 1918 flu, the 2009 H1N1 influenza, or now SARS-CoV-2, the transition to these viruses becoming a manageable threat was a combination of the virus evolving, immunity rising (for seasonal influenza and COVID-19, vaccination plays a critical role with this), and human behavior changing, Dr. Johnson explains. There’s evidence of SARS-CoV-2 changing just by looking at how quickly Omicron variant replaced Delta variant as the dominant circulating variant in many places. We can also see how high levels of immunity can help us more quickly contain a surge caused by a new circulating variant, Dr. Johnson adds. But our behaviors must change, too—that willingness as a society to come together and implement necessary public health measures to mitigate the impacts of virus spread is also important to making COVID-19 much more manageable. Dr. Michael Blaivas, MD, Chief Medical Officer at Anavasi Diagnostics explains that many threats can become manageable over time as the baseline resistance to the infectious agent increases in the population or the house of medicine finds a way to respond and tame the disease in some manner. “Unfortunately, in some cases of historic diseases, this meant those without resistance die out and those who are left may have had some genetic advantage to fight the disease and survive, such as in the case of smallpox,” Dr. Blaivas states. “Historically, (and relatively recently) we have been able to develop some treatments to manage threats, like in the case of HIV. For many years, HIV was a mysterious death sentence for all diagnosed, now it can be managed long-term.”
What is the likelihood that we will need booster shots every year?
As long as the disease is around to infect people, those at increased risk due to increased age and or chronic illness are likely to need regular vaccination or boosters similar to the flu, Dr. Blaivas explains. If the disease enters a low endemic state, there is a possibility that we could move away from early vaccinations. However, the real key may be the impact of any new antivirals that target COVID. “Personally, I think this is the best wild card we hold. We cannot be sure scientists will succeed in creating an ultimate COVID buster pill, but we have already had some success and have some good tools on our side," he said. “If we can get an effective oral antiviral, which dramatically decreases symptom/illness severity, then vaccination will be less relied upon.” Next up: Here’s What You Can Expect COVID Symptoms to Look Like Day-by-Day In Kids
Sources
Dr. Jennifer Haythe, Associate Professor of Medicine and Co-director of Columbia Women’s Heart CenterDr. Erica Johnson, Chair Infectious Disease Board, American Board of Internal MedicineDr. J. Wes Ulm, physician and medical researcherDr. Michael Blaivas, Chief Medical Officer at Anavasi Diagnostics
