President Biden and the CDC are hoping that the US COVID-19 death rate will be better for this current surge. We are optimistic but have doubts. The reasons are complex. For one, the US continues to test much less thoroughly than other best-in-class countries such as the UK. Thorough testing can identify and stop outbreaks before they become serious surges. Moreover, identifying a higher number of asymptomatic and mild cases causes the measured case fatality rate (CFR = deaths/cases) to improve since the denominator increases and the ratio decreases.
In the UK, the CFR appears to have improved significantly from 2.1% for the last wave in January to 0.3% for the current Delta surge. Part of the reason for the improvement is that the majority of Brits were vaccinated in early 2021 and the death rate for the vaccinated is much lower than for the unvaccinated.
The US hopes that a similar improvement will be observed. Unfortunately, this appears to be unlikely for a number of reasons.
1. The vaccination rate has been slower and lower in the US than in the UK.
2. The positivity rate is much higher in the US (~9%) than in the UK where it has stayed below 4% throughout this last surge.
3. The hospitalization rate in the US has already begun to soar.
4. The CFR has shown little improvement in the US this year.
This last point is crucial since it is the best predictor of deaths to come from cases and hospitalizations already in the pipeline. Lagged CFR is calculated by dividing the average deaths for the past 7 days by a weighted average of cases for the previous 2 – 4 weeks. Deaths usually take up to 20 days to resolve from case identification. Then some jurisdictions take up to 2 months additional to report those deaths. The graph below shows that after the initial confusion in early 2020, CFR improved dramatically and then stabilized around 1.5% for most of 2021. The fact that it hasn’t improved over the last 12 months is rather disappointing. It suggests that testing, tracking, and treatment of COVID-19 cases in the US has not improved in that time.
In recent weeks the CFR has actually deteriorated due to the very contagious and possibly more lethal Delta variant catching an unprepared American population. We expect the CFR to improve through the rest of the year for an unfortunate reason: the increasing prevalence of breakthrough cases as the effectiveness of vaccines begins to wane. Since breakthrough cases are more likely to be mild, only a fraction ~0.4% will result in deaths. As more and more people get vaccinated the CFR could drop to the 0.3% seen in the UK. We can only hope this happens soon. In the meantime get the vaccine if you haven’t yet, get the booster if your last shot was more than 6 months ago, and wear a mask and social distance as much as you can.