Things have been looking up lately with respect to the coronavirus pandemic. With transmission rates leveling out, it seems possible that we’re approaching the peak, and that we will, in the immediate term, manage to avoid many more desperate situations like those in Wuhan, Lombardy, and New York, where the number of people who were sick at the same time overwhelmed health systems and led to many avoidable deaths. However, this doesn’t mean that the epidemic has ended – in fact, if we don’t take the appropriate actions, things could still go very badly.
In order to understand why, it’s important to think about how disease transmission works. A large part of the reason why COVID-19 is so dangerous is because it had never infected humans before, meaning that nobody had any immunity. Immunity can be obtained either from having already been infected or from a vaccine, and can be partial or total, and long-lasting or temporary. On a group level, a lack of immunity means that the disease can spread quickly, since exposure to even a small amount of the virus is likely to make almost anyone infectious, even if they don’t exhibit symptoms.
We’ve successfully used social distancing to make coronavirus less “infectious” in the population, but social distancing only works when it is being used; the potential to be infected by coronavirus exists for anyone who hasn’t developed immunity. In order to prevent another destructive peak, enough people need to be immune so that it can no longer spread fast enough to overload health systems.
Large-scale immunity that prevents the spread of a disease is referred to as herd immunity. The herd immunity threshold, or the percent of the population that needs to have immunity to stop an epidemic from growing, can be calculated directly from R0, which is the measure of how many people one person typically infects. This value is affected by many factors, including not just the virus itself, but cultural and environmental conditions. As such, it’s very difficult to get an estimate for it, and values that apply in one place might not be useful in others.
Because the effective R0 changes with social distancing, it’s impossible to come up with any R0 value for “normal” conditions. This means that we need to rely on very rough estimates to figure out the herd immunity threshold. An R0 of 2.2 is fairly common, while statistically conservative estimates have given a range of 1.4-3.8. An R0 of 2.2 means that about 55% of the population would need immunity to keep the number of infections stable, while the broader range gives values of 28-74%.
In order to know whether we’ve reached herd immunity, we need to know how many people have been sick. Unfortunately, this is more complicated than it sounds.
There hasn’t been nearly enough testing of active infections in the United States, let alone the rest of the world, so the value of 650,000 total cases that is current as of the publication of this article is certainly inaccurate. It’s possible to use different statistical models and data from various countries to come up with estimates of underreporting; one preliminary report gives values that suggest a range of total cases in the United States from 2.5 to 6 million, corresponding to 0.8-1.8% of the total population. This is a very uncertain estimate, but it’s in line with predictions that many experts have put forward; besides, the number of people hospitalized in the US as a whole is significantly below the numbers in heavily affected areas, meaning that only a fraction of the population could have been exposed to the virus. That being said, direct testing for antibodies is currently in progress, and should provide a somewhat better idea in the weeks and months ahead.
Given that we are still almost certainly well below the herd immunity threshold, the outbreak will revive if social distancing measures are completely lifted. This shouldn’t actually come as a great surprise. Historical outbreaks, like the Spanish Flu, typically exhibited multiple peaks – and this in a time when the spread of disease was far less controlled.
Unfortunately, IHME predictions, which are used to guide US policy, still seem to suggest that the disease will be gone by the middle of July. Fortunately though, it seems that our society is slowly coming to terms with reality, thanks in part to Dr. Anthony Fauci advocating long-term changes.
These kinds of changes will need to be implemented on an individual, institutional, and government level – every successful intervention cuts the effective R0 down a bit further and decreases the likelihood of regional outbreaks (the extent to which we want to cut R0 well below 1, as we are hopefully doing right now with social distancing, is an important discussion, but one that has been covered elsewhere; for more information on this, refer to this paper and this critique of it. Regardless, until the right combination of interventions has been established and the government can provide coordinated instructions, it’s best to do everything within reason to continue to limit infection, especially when taking potential liability concerns into account).
On an individual level, it is important that we continue basic social distancing and hygiene measures. If supplies are available, it’s also a good idea to wear a mask in public; while the federal government still hasn’t come to a coherent conclusion, foreign governments have been mandating them for some time, and some states are coming around to the importance of them.
Businesses also play an important role in preventing the spread of coronavirus. Regular disinfection of workplaces is a must, as is setting up workspaces with good ventilation and sufficient space between employees. Those who can work from home should continue to do so; in cases where being physically present at work is at least partly necessary, managers should consider cycling employees, with only a handful coming into the office on any given day. For those employees that do come into work, consider coordinating lunch and snack plans in advance. Ensuring that employees do not need to leave work to get food will limit their chances of getting sick.
In addition, all businesses, especially restaurants and bars, should consider restricting access to individuals with a fever, as a handful of chains have already started to do; restricting access to employees based on body temperature seems to be legally tenable, but it’s advisable to consult with counsel before implementing this step regardless. In all cases, businesses should have clear protocols in place for how to deal with sick employees, both so that more employees do not get sick and so that business is as minimally disrupted as possible. Furthermore, all coronavirus-related policies must be clearly communicated to employees. In cases where employees might not speak English, it is imperative that information be provided to them in their native language.
Finally, there is a good chance that countries will begin to relax border restrictions; however, travel for business should still be restricted to cases where it is absolutely necessary, and it may be advisable for employees to remain at home after a business trip, given that they will likely interact with far more people in many different circles than when at home.
Assuming appropriate government measures, like aggressive contact tracing and testing, these actions should be enough to effectively stop the spread of the disease while keeping the economy running. After all, Taiwan and South Korea adopted similar measures, and have been in a post-peak world since the outbreak started.
It’s important to recognize here that the immediate aftermath is months and years, not weeks and months, as many people seem to be suggesting. There’s simply no chance of achieving herd immunity any time soon by keeping transmission rates at a manageable level – excepting the development of a vaccine, which is still at least a year away for most of us. Regardless of how long we might have to live with these new precautions, there’s no reason not to start planning now.