COVID-19 Breakthrough Cases

The CDC in the USA continues to lag the best-in-class by requiring minimal genetic testing and tracking of COVID-19 cases compared to the UK or Israel.  This has led to slower identification and monitoring of COVID variants and how mutations can change their infectiousness and speed of spread.  To date, the CDC monitors only a limited sample of those who are fully vaccinated and have serious hospitalizations and deaths, dropping their initial request for states to monitor all “breakthrough” cases.  This data is only voluntary – passive reporting by the county health departments that decide to participate.  This has led to erroneous conclusions about the speed and seriousness of the current COVID-19 Delta surge.

One very bad statistic that is often quoted is this: As of July 12, of the more than 159 million fully vaccinated people in the USA only 5,189 were ever hospitalized or seriously ill, and only1,063 died from COVID-19.  The conclusion that only 0.0033% of those fully vaccinated will get seriously ill (or 0.0007% will die) from COVID-19 is totally misleading.  The reason is that only a small percentage of fully vaccinated folks have been exposed for a short amount of time to COVID-19 in general and the Delta variant in particular.  Until recently the community exposure was only a few percent.  The community spread is now approaching 10% again as testing increasingly returns positive results.  Another popular statement is that of the 170k Americans who have died from COVID this year only 1k were fully vaccinated.  Since this is less than 1% the conclusion is that the Delta surge is a pandemic of only the unvaccinated.  Again this is extremely misleading since the percent of all Americans fully vaccinated at the beginning of the year was very small and only approached 50% recently.

A more relevant and accurate way to assess breakthrough cases and deaths is to look at what has happened recently.  Using the CDC data for the week of 7/13-7/19, we note that 725 serious hospitalized cases and 78 deaths were reported as breakthroughs likely associated with COVID-19.  This should be compared with the 1,978 COVID deaths reported for the week.  Thus 4% (= 78/1978) of all deaths were breakthrough deaths.  These deaths resulted from the infected population over the previous 1-4 weeks which we estimate to be 110,000 in total (see Table below).  This makes the overall lagged case fatality rate, CFR, 1.8% (= 1978/110000).  Segmenting this data into fully vaccinated and unvaccinated folks we estimate that the CFR for fully vaccinated people is 0.3%, far better than the 2.4% experienced by the unvaccinated – a clear incentive to get vaccinated.  This segmentation data also suggests that 30k breakthrough infections occurred over the past 1-4 weeks.  Most of these were asymptomatic or mildly symptomatic so few noticed them and no health authorities tracked them. Anecdotal reports of breakthrough cases among athletes and select populations were dismissed since they were nearly all mild. 

The mRNA vaccines are a remarkable scientific achievement, and much better than most vaccines, but they are not perfect and should not be oversold as such.  They reduce the chance of death by 91% but may only reduce the chance of infection by 40%.  Many fully vaccinated people can still get the virus but their immune systems will have been primed to reduce the probability of serious illnesses and deaths (but not eliminate it).  They are also less likely to carry a viral load large enough to transmit as effectively as unvaccinated people (although some say the Delta variant can increase viral loads a thousandfold), but there is little doubt that they can transmit the Delta variant.  In fact, that they lead to so many asymptomatic cases may be what is exacerbating the latest surge because of the prevalence of silent carriers.  Thus the CDC miscommunicated recommendation to discard indoor masking without verification should be corrected immediately.  Masking and/or social distancing should be recommended outdoors.  Vaccinations should be required for all Federal personnel and for entry into Federal facilities.  The best way to ensure compliance is to require vaccine passports.  Each day’s delay in implementation is costing thousands of Americans their lives and livelihood.