Let's Reminisce: From pandemic to endemic
Covid-19 will soon become endemic—and the sooner the better. An epidemic causes widespread disease in a region. A pandemic affects multiple countries or continents. A disease becomes endemic when it is manageable—defined as not causing an undue burden on hospitals or other healthcare resources—but unlikely to be eliminated.
Australia, China and New Zealand have pursued “zero Covid” policies that aim at elimination (reducing incidence in a region to zero) or even eradication (world-wide elimination). That goal is unrealistic. Smallpox is the only human disease that has ever been eradicated. The smallpox virus has had four properties that made it eradicable: the lack of an animal reservoir, clear and distinctive signs and symptoms, a short period of infectiousness, and both lifelong natural immunity after survival and a highly effective vaccine.
Covid-19, by contrast, is unlikely to be eradicated. It has animal reservoirs, a high level of transmissibility (especially of the Delta variant), and overlapping symptoms with other respiratory diseases. It has, as well, a prolonged period of infectiousness, caused by its propensity to spread from asymptomatic carriers.
That’s why reducing the disease from epidemic to endemic is the best case—one that will allow a full return to normal. Many ineradicable infections are controlled by vaccination and treatment. Measles, a highly transmissible respiratory virus, created high levels of immunity among adults who were exposed as children. But until a vaccine was developed in 1963, some non-immune adults died every year.
Officials tried a wide array of measures to control Covid-19: masks, social distancing, lockdowns, travel restrictions, ventilation, testing, contact tracing. These had varying levels of success but ultimately proved insufficient to control the virus. That will require widespread immunity. Fortunately, safe and effective vaccines were developed in record time. These vaccines are the key to turning Covid-19 into an endemic but controlled communicable disease.
Control means the reduction of serious disease. Since the vaccines are remarkably effective in preventing severe disease from Covid-19, they can serve as the conduit for control.
Antibodies generated by the vaccines will naturally wane, but the vaccines trigger the creation of B cells that get relegated to our memory banks. Memory B cells are long-lasting.
What would endemic Covid-19 look like? If we can tamp down the virus’s circulation and reduce its ability to cause severe disease through widespread vaccination, the world will be able to return to normal. Outbreaks of severe disease will occur among populations unwilling to be vaccinated, as we see with measles, but mandates can help increase vaccination rates.
As circulation of the virus decreases with increasing immunity, Covid-19 will go the way of other respiratory viruses over which we have control. We will test those who arrive at the
hospital for a variety of infections—including influenza, Covid-19, and bacterial pathogens—and tailor treatments to the infectious agent. Moderate respiratory symptoms of Covid-19 in the outpatient setting may be treated with antibodies, and mild symptoms (like other common colds) won’t require treatment.
The burden of disease a country is willing to accept will depend on its priorities: Denmark dropped all restrictions at a 74% vaccination rate and low cases on Sept. 10. Many U.S. states had an undue burden of hospitalization during the Delta wave, although California is keeping restrictions in place despite low hospitalization and high vaccination rates. We will need to accept that the disease is endemic. A low burden of disease should facilitate the transition.
Although Covid-19 has proved unpredictable, no virus in history has ever continued to evolve to higher pathogenicity. As we learned from HIV, mutations usually incur costs to viral fitness or render the virus weaker. No vaccine-preventable or immunity-inducing infection has ever raged on as a pandemic indefinitely.
An endemic virus doesn’t require continuing isolation and other restrictions. The key to this normalcy is immunity. With a highly transmissible variant driving up immunity in the unvaccinated and bolstering it in the vaccinated, Covid-19 will inevitably make the transition from epidemic to endemic.
Jerry Lincecum is a retired Austin College professor who now teaches classes for older adults who want to write their life stories. He welcomes your reminiscences on any subject: firstname.lastname@example.org.