We’re starting to see the first results from antibody testing to try to determine how widespread COVID-19 infections have been. We now have multiple studies reporting infection rates in the 2-3% range. Reactions to these results have been mixed, with some saying that are alarmingly high and others lamenting how low they are. I want to try to shed a little light on the hubbub.
First, take all of these studies with heaping helpings of salt. They’re an important step, but they are rife with problems. The tests that are being used are not adequately validated and are neither as sensitive nor as specific as we would normally want. The studies themselves have often not been peer-reviewed and use questionable sampling techniques. In some cases the statistical techniques used to generalize the results are questionable. These are just first steps in the scientific process of coming to understand the virus. They will not be the last.
With that said, for this post I’m going to ignore all the problems with the studies and focus on the significance of the claim that 3% of the population has had some level of infection. This level of infection is ten times higher than the number of confirmed cases. If 3% of the population has been infected, is that good news or bad news? The short answer is – both.
Good News!
The primary way in which this might be good news is that it means the fatality rate might be lower than thought. The infection fatality rate is the number of deaths divided by the number of infections. As of last night, that was 42,970 / 800,970 = 5.4% for the US. If the infection rate is really 3% of the population, then that becomes 42,970 / 9,900,000 = 0.4%. That’s a lot better! Although it’s still 4x the fatality rate of a typical seasonal flu, such a lower rate would be a reason to think that we might be able to relax social distancing much sooner than with the higher fatality rate. We’d be dealing with a bad flu rather than something far deadlier.
However, these numbers don’t take into account the fact that there are likely more deaths from COVID-19 than have been reported. Studies comparing total deaths in the last month to what would be typical indicate that death rates may be 2 or more times what is reported. Still, that would increase the fatality rate to 0.8%, which is still a lot lower than 5.4%.
Beyond that, if 3% of the population has antibodies to the virus, then such people may be at reduced risk and might form the core of a workforce that could safely get the economy starting back up.
Bad News!
If 3% of the population has already been infected, then the virus has spread much more quickly than we thought. This means that opening up the economy will likely lead to a greater resurgence of the virus than anticipated. It means that COVID 19 may be as infectious as smallpox rather than only as infectious as the 1918 Spanish flu pandemic. Estimates of R0 for COVID-19 have been as high as 5.7, near the top of the estimated range of smallpox, and such estimates are more credible if the infection rate is already at 3%.
This also means that we are nowhere near the peak of this pandemic. Even assuming that those with antibodies are fully immune, herd immunity for an R0 of 5.7 would not kick in until more than 80% of the population was infected. We’re less than 1/25th of the way there. Even with the lower fatality rate, and assuming that we manage to not overwhelm the medical systems, getting to herd immunity would mean around 2 million deaths in the US and around 50 million world-wide. That’s a lot.
Takeaways:
These sorts of studies are important, but are just the beginning of the scientific process of understanding the COVID-19 pandemic. Research is still very fluid, and the lack of usual protocols and reviews will make for wildly different conclusions in the short term. Don’t get too attached to the conclusions until there is some level of consensus.
Although it seems like we’ve been at this forever, we’re really still in early days and are struggling to find the most graceful way through while satisfying the competing goals of minimizing deaths and minimizing economic harm. Try to find your isolation groove so that you’re comfortable with your situation but able to adapt to changes that will undoubtedly come. Try to balance realism and a positive mental attitude to help you and yours weather the uncertain future over the next several months to few years.