No pandemic is forever

Every pandemic has a beginning, a middle, and an end. Believe it or not, the end is in sight.
A Spanish flu victim is carried on a stretcher
With masks over their faces, members of the American Red Cross remove a victim of the Spanish Flu from a house at Etzel and Page Avenues, St. Louis, MIssouri, 1918. St. Louis Dispatch.
A Spanish flu victim is carried on a stretcher
With masks over their faces, members of the American Red Cross remove a victim of the Spanish Flu from a house at Etzel and Page Avenues, St. Louis, MIssouri, 1918. St. Louis Dispatch.

After nearly a year of social distancing, wearing masks, and Zoom family gatherings, many of us are either impatient for it to be over, or have resigned ourselves to an indefinite cycle of lockdowns alternating with new waves of infection. Reports of slow vaccination rollouts, partial viral escape variants, and new viral surges in places previously thought to have reached herd immunity have led authorities to warn that the virus will be with us for a very long time, perhaps even permanently. But that’s a misleadingly pessimistic take on the natural cycle of pandemics and the capabilities of science. What follows here is a synthesis of three twitter threads charting out a realistic post-pandemic transition from leading experts in public health, epidemiology, and virology.

David Fisman, MD, MPH is an epidemiologist with the Dalla Lana School of Public Health in Ontario. He says he’s optimistic about “a non-reckless return to normalcy over the medium term.” Fisman explains that all pandemics have a beginning, a middle, and an end. For example, descendants of the the Spanish flu virus, H1N1, thought to have killed 40 million people, continue to circulate to this day. Yet the Spanish flu pandemic of 1918-1919 was over by 1922. What changed? According to Fisman, it was population susceptibility.

As the population acquires immune experience with a new virus, the number of new cases from each infection, the R(0), drops due to a lack of susceptible hosts. “The basic idea is that the pandemic itself seals its own doom by depleting population susceptibility, just as a forest fire ensures its own end by burning up all the fuel,” says Fisman.

The forever pandemic is a myth borne of despair. Like all pandemics in human history, this one has an expiration date. When that will be, what it looks like, and how many more people will die depends on how effectively people and governments can cooperate in suppressing the spread of the virus and distributing vaccines.

Unfortunately, the decline in R(0) is transient. Susceptibility to the virus will replete, due to waning antibodies and, over the long term, birth of new generations that have never been exposed to the virus or vaccinated. Additionally, viral variants emerge that escape immunity, leading to recurring outbreaks. These new outbreaks don’t constitute a full pandemic, however, because overall there are still a lot of people with immunity, keeping the R(0) value low. “So be confident,” tweets Fisman. “The idea of a forever-pandemic is about as plausible as the idea of a forever-forest fire.”

We currently have two routes for depleting that susceptibility—natural infection and vaccination. Vaccinations are going slow, for now, at about 1.3 million per day. However, in news that is both good and bad, a model by Columbia University infectious disease specialist Jeffrey Shaman, shows that one third of the US population, or about 120 million Americans, have already been infected—already a significant depletion of susceptibility of the population. (via NPR)

The endemic phase

Experts have predicted a post-pandemic period in which SARS-CoV-2 is still circulating, but not at pandemic levels. Does that mean it’s endemicUniversity of Oxford virologist Aris Katzourakis has some thoughts, “I am not convinced that people quite understand what endemic means. An endemic virus is a virus where infection levels are maintained at a baseline level without external inputs. Chickenpox is endemic; HIV is not, as it is still spreading.”

According to Katzourakis, an endemic virus exists in equilibrium, with an R(0) exactly 1. That means each infected person passes the virus on to only one other person. However, even if SARS-CoV-2 achieves that steady state, that “endemic” level of infections might not necessarily be low. A virus could be endemic at high numbers of infections and deaths. A low-level endemic virus, with very low numbers of infections and no serious disease, would be a “fantastic outcome,” says Katzourakis.

Most discussions of a post-pandemic SARS-CoV-2 that has become endemic do not take into consideration the emergence of new strains which would continue to drive erratic and potentially highly deadly epidemic waves. “This is the future if we do not go for maximum suppression, not some stable endemic state, at least not in timescales that are relevant to public health outcomes,” says Katzourakis.

Looking ahead

The good news is that suppression is achievable through continued public health interventions and vaccination. Let’s look at Ashish K. Jha’s recent thread on vaccination, “Feeling pessimistic about COVID & 2021? Don’t!

Jha points out that although vaccines are rolling out slowly now, with limited supply, production is ramping up quickly and should be available to most people in the US by summer. This week, President Joe Biden announced the purchase of an additional 100 million doses each of the Pfizer and Moderna vaccine. That brings the total vaccine buy to 600 million doses, to be delivered by the end of July. That’s enough to vaccinate 300 million Americans. As well, coming soon, new vaccines from Johnson and Johnson, Astrazeneca, and Novavax are likely to be approved. Meanwhile, distribution logjams are being cleared, and Jha expects 2-3 million vaccinations per day in March and April, and 150 to 200 million vaccinated by July 1.

The forever pandemic is a myth borne of despair. Like all pandemics in human history, this one has an expiration date. When that will be, what it looks like, and how many more people will die depends on how effectively people and governments can cooperate in suppressing the spread of the virus and distributing vaccines.