Breakthrough infections rare among first 101 million fully vaccinated people, CDC finds
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CDC investigators identified just 10,262 breakthrough SARS-CoV-2 infections in 46 U.S. states as of April 30, when approximately 101 million Americans had been fully vaccinated, according to results published today in MMWR.
“Even though FDA-authorized vaccines are highly effective, breakthrough cases are expected, especially before population immunity reaches sufficient levels to further decrease transmission,” members of the CDC’s COVID-19 Vaccine Breakthrough Case Investigations Team wrote. “However, vaccine breakthrough infections occur in only a small fraction of all vaccinated persons and account for a small percentage of all COVID-19 cases.”
The CDC team worked with state and local health departments to identify SARS-CoV-2 infections in fully vaccinated persons. They defined a breakthrough infection as the detection of SARS-CoV-2 RNA or antigen in a respiratory sample from a patient 14 days or more after the administration of the final dose of a COVID-19 vaccine. Some specimens were also submitted for genomic sequencing.
Of the breakthrough infections, 63% occurred in women, the median patient age was 58 years (interquartile range = 40-74 years), and 27% were asymptomatic.
According to the report, 2% (n = 160) of patients with a breakthrough infection died and 10% were hospitalized. Of the 995 hospitalized patients, 29% were hospitalized for a reason unrelated to COVID-19 or did not show symptoms. SARS-CoV-2 variants accounted for 70% of the estimates of SARS-CoV-2 lineages obtained by the CDC.
The investigators noted two major limitations of their analysis: potential underreporting of breakthrough cases, and sequencing data being available for only a “small proportion” of cases.
“CDC will continue to lead studies in multiple U.S. sites to evaluate vaccine effectiveness and collect information on all COVID-19 vaccine breakthrough infections regardless of clinical status,” they wrote.
Perspective
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The CDC MMWR confirms that the COVID-19 vaccines are highly efficacious, and when breakthrough infections occur, they almost always do not have major clinical significance requiring someone to be hospitalized. It also does not appear that the breakthrough infections show any type of pattern in terms of variants that differ from the proportion of variants that are circulating in the country at this time, further underscoring the efficacy of the vaccines. I think it is important to focus on breakthrough infections that have clinical significance, as the CDC is doing.
No vaccine is 100% protective; however, these vaccines against COVID-19 are some of the best that we have ever seen and the rare breakthrough infections do not change that fact. It’s also important to shift from looking at cases to looking only at serious disease because the vaccination of high-risk individuals has decoupled cases from hospitalizations and deaths — this is what flattening the curve was initially about.
Perspective
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These latest CDC numbers are welcomed and continued evidence of the dazzling power of the vaccines in the U.S. (even against the feared variants), and corroborate studies conducted in the United Kingdom and Israel and smaller subpopulation studies. Even given the limitations of not having all asymptomatic infections tallied, you are much more likely to get struck by lightning than get a breakthrough infection, or killed by a meteor than succumbing to COVID-19 following a vaccine. We expect even smaller odds of breakthrough infections and deaths as the amount of circulating virus drops precipitously once enough of us in the herd are protected. The shift of the CDC to now only intensively study breakthrough hospitalizations and deaths, rather than all infections, is appropriate. After all, these are the most important outcomes we care about when assessing a vaccine’s worthiness.
Perspective
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Overall, these data should reassure us that SARS-CoV-2 vaccines are doing exactly what we need them to do: provide very high levels of protection, even when community transmission remains high. The fact that breakthrough infections occurred in people who were demographically similar to the vaccinated population at large is also reassuring, suggesting that these events were part of the inevitable rollout during a period when many areas were still struggling with high incidence. Finally, these data don’t suggest a specific role for “new” variants in driving these breakthroughs.
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