Recently, there has been a great deal of media chatter about people falling sick with COVID after being vaccinated or after recovering from a previous COVID infection – dubbed “breakthrough” infections.  We have almost no data on reinfections because there is no comprehensive database on who has had COVID.  In fact, we only have guesses about how many people have actually contracted COVID because there are so many people who have had no or mild symptoms and never sought treatment.

We have more information about breakthrough infections after vaccination but only as it relates to serious cases.  Early on, the CDC attempted to track all breakthrough cases but quickly realized the futility in doing so.¹   It currently only reports breakthroughs resulting in hospitalizations and fatalities.

The principal source of data on breakthrough infections after vaccination is the CDC’s COVID-19 Vaccine Breakthrough Case Investigation and Reporting website.  According to the site, 5,226 individuals have died from COVID after being fully vaccinated and 16,889 have been hospitalized as of September 27. The earliest that anyone could have had the benefit of being fully vaccinated would have been about the first of February.  Since then, the CDC reports that 228,686 people have died from COVID and that 1.5 million people have been hospitalized with COVID.  So, if the CDC breakthrough data is accurate, breakthrough infections only account for 2.3% of all COVID fatalities and 1.1% of all COVID hospitalizations.  In other words, 97-98% of the people who died from or have been hospitalized with COVID since the vaccines were available have been unvaccinated.

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However, there are a few of important caveats.

First, I think it is quite likely that the CDC breakthrough data is incomplete.  As I understand it, this data flows from the hospitals to the CDC.  So, the CDC is at the mercy of the hospitals reporting the data and reporting it accurately.  I have no way to judge how well that system is actually working.

Second, the CDC’s website is only reporting static information with no ability to track breakthroughs over time.  So, we do not know how breakthrough infections have changed over time, a datapoint that would be especially important once Delta emerged and would help us determine if vaccine-induced immunity is waning over time as some studies have suggested.

I talked to Dr. James McDeavitt, who is in charge of Baylor College of Medicine’s COVID response, about how breakthrough hospitalizations have changed over time.  He said the TMC hospitals saw almost no breakthrough cases for the first six months but that in the last two months they have increased substantially, averaging at about 10%.  If you average six months at, say 1%, and two months at 10% that would give you about 2%, which is in the range that the CDC is showing nationwide.

It is important to remember that we never expected the vaccine to perform in certain individuals whose immune systems are compromised.  Mark Boom, the Houston Methodist CEO, made this point recently in one of their COVID Townhalls, noting that the breakthrough rate at his hospital is running higher because it performs so many transplants which require patients to take immuno-suppression drugs to prevent rejection of the transplanted organ.  Similarly, individuals who have been treated with radiation or chemotherapy can have weakened immune systems.  This 2016 study estimated that over 10 million Americans have weakened immune systems.

Third, the vaccines did not do all this work on their own.  Shortly after the first of the year, the FDA approved two monoclonal antibody treatments, specifically designed to keep patients with COVID from developing a serious case that would require hospitalization.  The federal government is currently shipping nearly 200,000 of these treatments per week.  Clearly, some of those are going to breakthrough cases and reducing hospitalizations and fatalities in vaccinated individuals.

But even taking those caveats into consideration, the bottom line is that the vaccines are performing as good, if not better, than what the trials predicted. And more importantly they done astonishingly well at accomplishing their principal mission of reducing the number of serious outcomes from COVID infections.  The data clearly shows that if we had done a better job of rolling out the vaccine, especially before the Delta wave, there would have been fewer COVID deaths and hospitalizations.

Note 1 – Attempting to track all breakthrough cases suffers from the same limitations we have seen in trying to track COVID cases generally.  Because COVID presents in such a wide range of symptoms in different people, many asymptomatic cases or cases with mild symptoms are never tested or reported.  Because the vaccines are designed to reduce the virus’ effect on the body, infections after vaccination are even more likely to be missed.  Also, testing sites generally do not inquire about whether a person has previously been infected so the CDC quickly realized that the breakthrough case data was a mess.