The Delta variant was first identified in the United States in April and by May it was well onto its exponential growth curve, doubling every 10-12 days, as the basis for Covid infections, now reaching over 96% prevalence. Ironically, on 1 May, the CDC announced it would stop monitoring post-vaccination breakthrough infections unless they led to hospitalizations or deaths. This decision can be seen as exceptionally ill-advised and has led to a country flying blind in its attempt to confront its fourth wave of infections – one that has rapidly led to well over 100,000 new cases per day and more than 60,000 hospitalizations, both higher than the US first and second pandemic waves. It is unfathomable that we do not know how many of these are occurring in people who were vaccinated.

Most people who get Covid infections after being fully vaccinated have mild to moderate symptoms, and generally have been thought to avoid hospitalizations. But that sense of confidence about vaccine protection was built upon the pre-Delta data when the CDC was monitoring breakthroughs. Still being reported by CDC, from their latest website data, and a constant refrain from public health officials, is that “99.99% of people fully vaccinated against Covid-19 have not had a breakthrough case resulting in hospitalization or death.” That could not be further from the truth. In the July Provincetown Delta outbreaks that the CDC reported on the risk of fully vaccinated requiring hospitalization was 1%, not .01%, and that may not be a reliable estimate for the incidence of such infections occurring throughout the country.

Why is this so critically important? For one, the false sense of security transmitted by CDC’s lack of data in the Delta wave likely fosters complacency and lack of protective measures such as masks and distancing. The mission of the CDC to prevent such illness, and the first step is to collect the relevant data. It would be very simple to know the vaccination status of every American with a breakthrough infection admitted to the hospital with Covid-19, along with key demographics such as age, time from vaccination, which vaccine, and co-existing medical conditions. The PCR diagnostic test for each patient has an accompanying cycle threshold (Ct) value, which is an indicator of viral load, and would be important to track. Moreover, the sample of the virus could undergo genomic sequencing to determine whether there has been further evolution of the virus and blood samples for neutralizing antibody levels that could be obtained in as many patients as possible. Contact tracing of these individuals would help determine the true rate of transmission from other vaccines, something that is pure conjecture. Such systematic collection of data would be the foundation for understanding who is at risk for breakthrough infections, determining the current level of effectiveness of vaccines and whether, when, and in whom, booster shots should be recommended. It is remarkable that none of this is getting done for hospitalized patients, who represent an undetermined fraction of the people who are getting quite ill, some requiring monoclonal antibody infusions to pre-empt getting admitted.

This is not by any means the first breakdown of the CDC in managing and communicating about the pandemic. But with billions of dollars allocated to CDC earlier this year for improved Covid-19 surveillance, this represents a blatant failure that is putting millions of vaccinated Americans at unnecessary risk for breakthrough infections and leaving us without a navigational system for the US Delta wave.