The acting head of the Centers for Disease Control and Prevention defended himself against criticism for his decision not to publish a study on the efficacy of last year’s COVID-19 vaccines.
Jay Bhattacharya, the director of the National Institutes of Health and senior official carrying out the CDC director role, published an opinion piece on Thursday pushing back against intense criticism for withholding the publication of the Morbidity and Mortality Weekly Report on COVID-19 effectiveness last week.
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Critics have said Bhattacharya withheld the report to hide evidence that would support people getting the vaccine next year, in line with anti-vaccine rhetoric supported by Health and Human Services Secretary Robert F. Kennedy Jr.
But Bhattacharya said his decision to nix the report was due to methodological problems with studying vaccine efficacy rather than the results of the study itself, adding that such a decision “falls squarely within the CDC director’s responsibilities.”
“The CDC is not withholding data — it is upholding its responsibility to ensure that every piece of information it shares is rigorously validated, accurate and worthy of public trust,” Bhattacharya wrote in the Washington Post.
In particular, Bhattacharya questioned the study’s test-negative design, which only includes people who have symptoms. That means people who were vaccinated but did not experience COVID-19 symptoms were not included in the study, which Bhattacharya said could skew the results.
“The vaccine effectiveness estimates this method yields could be an overestimate or an underestimate; it’s impossible to tell,” Bhattacharya wrote.
The results of the report were not overwhelmingly positive for COVID-19 vaccine efficacy, according to a draft report obtained by MedPage Today earlier this week.
In the last four months of 2025, those who received the COVID-19 vaccine were only 50% less likely to have an associated emergency department or urgent care visit and were only 55% less likely to be hospitalized with COVID-19 than those who were not vaccinated.
As of February, the end of the seasonal virus cycle, only 17.5% of American adults and 9.5% of children received the COVID-19 vaccine, according to the most recent CDC data.
Bhattacharya also said the decision to pull the study was part of his broader reform to implement a new peer-reviewed journal published by the CDC.
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The Morbidity and Mortality Weekly Report is not peer-reviewed, meaning that outside scientists review the methodology and findings of a study to ensure it is sound. The Morbidity and Mortality Weekly Report has never been peer-reviewed because it is traditionally seen as the voice of the CDC on particular issues and because peer review slows down publication time.
Bhattacharya was named the acting CDC director, in addition to his role as the head of the NIH, in March during a leadership shake-up at HHS. He will serve in the leadership position at CDC until President Donald Trump’s nominee, Dr. Erica Schwartz, is confirmed by the Senate as director.
