In a recent interview, Dr. Anthony Fauci (Director of the National Institute of Allergy and Infectious Diseases and the Chief Medical Advisor to the President) said that Covid-19 is no longer in the pandemic phase in the United States. Specifically, Covid-19 has entered a transitional phase between a pandemic and an endemic disease, where infection rates are dropping but Covid still poses a significant risk. So with this announcement and several jurisdictions rolling back mask mandates, I think it’s time to talk about what this statement means, what it doesn’t mean, and where we should go from here.
Endemic
I’ve talked before about the concept of endemic diseases, but to reiterate, a disease is said to be endemic to a region when each infected person infects on average only one other person. This means that the number of active infections within the population can neither increase or decrease, so infection numbers stay at a fixed amount indefinitely. The vast majority of diseases one is at risk of getting in their day-to-day life are endemic diseases, such as the common cold. An epidemic is when the average infected person infects more than one other person, so the disease is constantly producing more infections within a given region. A pandemic is when a disease is epidemic in multiple regions or across the whole world. But as more people become vaccinated or infected with a disease, more people become immune, meaning the disease can no longer spread to those individuals. As the number of infectible people diminishes, the infection rate falls. This is how all epidemics and pandemics end; they burn out the surplus of available fuel and become endemic diseases.
It should be noted that this is the mathematical definition of an endemic disease, but determining this in the real world is more complicated. Specifically, once a pandemic disease’s Re falls below 1, it could still behave like a pandemic disease for some period of time due to the sheer number of infected people. There isn’t a formal non-mathematical definition of an endemic disease, so there isn’t any threshold or warning signs that can definitively tell us that we’ve entered that stage. Some scientists have even said that one can’t determine if a disease has become endemic while it’s happening, that one can only tell in hindsight. So, how close is Covid-19 to becoming an endemic disease? Well, for much of the world, infection rates are decreasing. While there is often significant variance between the Re of different regions, as regions with higher population density or lower vaccination rates can have higher-than-average infection rates, the average Re of most nations is now around or below one. Taking the United States as an example, Covid-19 has an average Re calculated to be roughly between 0.96 and 1.14, depending on data sources. I’ve listed a few sources below to find both the effective reproduction number and the number of new infections for where you live.
So What Now?
As stated before, this isn’t the end of the Covid-19 pandemic so much as it is the transition into a new stage. Covid-19 becoming an endemic disease does not mean that there won’t be infections or deaths, at least not immediately. What it does mean is that the disease will be predictable. An endemic Covid-19 could look a lot like the flu, the scientific infrastructure of which I’ve talked about before. Covid would continue to mutate and potentially create new strains, but it would do so slowly enough that specific vaccines could be developed before these strains could become a serious problem. We might see localized epidemics, where there’s a significant uptick in cases within a particular region, but this limited scope would make it easier to provide emergency services to prevent hospital overcrowding. It’s possible that there could be times of year where Covid is more serious, which would make it easier to prepare for, though most scientists think Covid won’t be tied to a particular season.
It should be noted that while Covid-19 has entered this transitional stage in the United States, it’s still very much a pandemic to the wider world. There are nations where, due to higher urban density or to less access to vaccines, Re is still fairly high. The main concern about regions with high rates of Covid infection is that they are breeding grounds for new variants, which could then spread to other regions. New Covid variants are the big unknown of this new stage. The emergence of new variants have repeatedly pushed the predicted end of the pandemic back, and the recent substrains of Omicron are continuing to cause a slight uptick in cases. Our current vaccines have proven to be reasonably effective at limiting the symptoms and spread of Covid variants, so a new variant being introduced to an endemic region might not be enough to start a new epidemic. But it’s not possible to determine this with the data we have now. The best practical thing to do would be to get vaccinated and boosted while also supporting policy that encourages the sharing of vaccines with regions where the pandemic is still active. This would reduce the spread of Covid worldwide, thus making it harder for new variants to evolve.
On a slight tangent, you may have heard that new variants of Covid are expected to evolve to be less deadly until the virus itself no longer poses as big a threat. This is based on an old theory in epidemiology that viruses always evolve to become less dangerous as it benefits the species in the long run to not kill their hosts, much like it behooves you to not burn your house down. But this theory has been pretty thoroughly debunked. Evolution is not so simple that there is only ever one strategy to increasing an organism’s ability to survive. Yes, becoming less likely to kill the infected host could mean that the host lives longer and can spread the virus to more people. But many of the ways that viruses kill their host (lung infection, high fever) directly relate to the methods used to make themselves more infectious. It’s just as likely that new strains could be more deadly as a side effect of the methods they use to spread. Whether future strains are more or less dangerous ultimately comes down to what mutations appear first.
This brings me to my final point; what should we be doing as individuals to protect ourselves and our communities? While scientists do acknowledge that the pandemic is transitioning into this new stage, there has been criticism of how quickly some mask mandates and other Covid protections are being rolled back. Again, Covid hasn’t abruptly disappeared, it’s waning in part due to these measures. So there is a fear that repealing these measures is more political than scientific and that it could give a false impression of how safe we actually are, especially those who are elderly or immunocompromised. As usual, the best thing any individual can do to protect themselves and others from Covid is to make sure they are fully vaccinated and boosted. Additionally, this article from the New York Times gives good practical advice on when one should wear a mask. To summarize, one is probably safe without a mask outside unless standing shoulder to shoulder with other people. While inside, consider the height of the ceiling, the air flow, and the number of people. A good rule of thumb is that if cigarette smoke would quickly fill the space if a person were smoking within it, then aerosolized viral particles can do the same so it’s best to wear a mask. Always wear a mask on airplanes or public transit, and in any establishment that requires them. Remember to consider the most vulnerable people whom you regularly interact with when deciding how much unmasked interaction you should allow yourself.
Now more than ever perhaps, it is important to listen to experts on what is needed to remain safe. The steps needed to limit infection are somewhat more complicated and it would seem that political institutions won’t always reflect that complexity. This is not the end of Covid-19 or the threat it poses. Instead, it is two years of effort finally starting to pay significant dividends. The sad fact is that this pandemic will not come to a narratively satisfying stop, instead it will fade so gradually that no one is likely to notice when it truly concludes. But it is still an ending, which is the only thing that ultimately matters.
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