The results of two California antibody studies have found that the portion of the population that has been exposed to COVID-19 may be much higher than we knew. The two tests were conducted by researchers at Stanford and USC in Santa Clara and Los Angeles, respectively. The Stanford study found that the likely infection rate was 50-85 times higher than the confirmed cases. The USC study found a rate of infection 28-55 times higher.
Before thinking about what this might mean, please understand that the results of these studies are very, very preliminary and there has been a fair amount of controversy about the methodology, especially as it relates to the Stanford study. [See here and here.] However, the results are consistent with some other anecdotal evidence that the virus is more widespread than previously thought. For example, a maternity ward in New York began testing all incoming patients and found 15% were positive. Dr. Scott Gottlieb, former FDA Commissioner, recently said he thought the infection rate could easily be ten times the confirmed cases and I heard a TMC CEO say he thought it might be a hundred times greater.
So, while keeping in mind the caveat that these studies are very preliminary, what are the implications if there are many times more infected people in the U.S. than we thought?
Of course, initially, it means that the virus is much more contagious and much less lethal than has been estimated so far. For these tests to be anywhere near accurate, the virus would have an “R-naught” factor of over 2 but a fatality rate well below 1%.
At that level of contagiousness, the virus will likely burn through the population until we reach herd immunity – probably regardless of what we do and long before we have a vaccine.
If that is the case, how should we react? The Los Angeles County Public Health Director reacted to the study by saying it showed we should double down on social distancing and other containment strategies. It strikes me that the results suggest exactly the opposite conclusion.
Herd immunity is achieved when a virus tries to jump from an infected person to the next person, but that person has previously been infected and has antibodies to kill it off. For a virus with an R-naught of 2, we need about 50% herd immunity. At that point, half of the time the virus tries to jump it is killed off instead of spreading to another person. So, every person who becomes infected and recovers becomes another dead end for the virus. Social distancing delays healthy people, who can fight off the virus, from being infected delaying them from becoming dead ends and, thus, from us achieving herd immunity.
The problem with getting to herd immunity, is that while doing so the virus will occasionally jump to someone whose immune system cannot fight it off and they will die. That is why the hospitalization and fatality rates are so critical. If those rates are high, containment strategies make sense to prevent the healthcare system from becoming overwhelmed, resulting in unnecessary fatalities. But if those rates are low enough that the demand on the healthcare system is manageable, then containment strategies will delay achieving herd immunity and prolong the epidemic which will also result in unnecessary fatalities.
We know that the fatality rate is not uniform across the population. From the clinical experience we have a pretty good idea who is likely not going to be able to fight off the virus. If someone is old, obese or has a pre-existing condition (especially respiratory related), we cannot chance exposing them to the virus.
So, (i) if the fatality rate is much lower and (ii) we know who is likely to succumb to the disease and (iii) the virus is much more contagious, the rational strategy would be to aggressively protect those most in danger but otherwise let the virus burn through that portion of the population that will be able to fight it off. That way we achieve herd immunity as soon as possible.
I think it is important to recognize that achieving herd immunity is the only way we are going to ultimately protect those who are vulnerable to the virus. Because we can only protect them for so long with containment strategies. The longer the virus is out roaming through communities, the more likely it is going to find its way into a nursing home or a vulnerable person in self isolation.
Again, I am not in any way suggesting this is a policy shift we should immediately adopt. But if more antibody testing begins to confirm what these initial tests have found, we need to rethink what we are doing.