CDC Acting Director Delayed Release of COVID-19 Vaccine Effectiveness Study

Apr 11, 2026

Acting CDC Director Dr. Jay Bhattacharya delayed publication of a COVID-19 vaccine effectiveness study that was scheduled to appear in the agency's Morbidity and Mortality Weekly Report on March 19, citing concerns about the observational methodology used to calculate vaccine effectiveness. The study found that COVID-19 vaccines reduced emergency room visits by 50% and hospitalizations by 55% during the previous winter. Bhattacharya has advocated for using randomized clinical trials instead, though such trials are often expensive and difficult to conduct quickly. Former CDC Chief Medical Officer Dr. Debra Houry stated that political appointee involvement in publication decisions would be highly unusual, noting that reviews were previously conducted by career scientists working across administrations.

Delay and Concerns Over Study Methodology

▪Dr. Jay Bhattacharya delayed the release of a U.S. Centers for Disease Control and Prevention COVID-19 vaccine effectiveness study while serving as the agency's acting director.
▪Dr. Jay Bhattacharya expressed concerns about the observational method used in the U.S. Centers for Disease Control and Prevention COVID-19 vaccine effectiveness study to calculate vaccine effectiveness.
▪Randomized clinical trials for vaccine effectiveness are often expensive and difficult to conduct quickly.
▪The U.S. Centers for Disease Control and Prevention COVID-19 vaccine effectiveness study findings were scheduled for publication on March 19 in the CDC's Morbidity and Mortality Weekly Report.
▪Dr. Jay Bhattacharya has suggested using randomized clinical trials instead of observational studies to measure vaccine effectiveness.

Study Findings on Vaccine Effectiveness

▪The U.S. Centers for Disease Control and Prevention COVID-19 vaccine effectiveness study found that COVID-19 vaccines reduced emergency room visits by 50% during the previous winter.

Unusual Nature of Political Involvement in Scientific Review

▪Dr. Debra Houry served as the U.S. Centers for Disease Control and Prevention's chief medical officer before resigning in August.
▪Dr. Debra Houry stated that previously, Morbidity and Mortality Weekly Report reviews would have been conducted by a career scientist who worked across administrations.
▪Dr. Debra Houry stated that a political appointee at the U.S. Centers for Disease Control and Prevention would very rarely be involved in a review or decision regarding the Morbidity and Mortality Weekly Report.
▪Observational studies are commonly used to measure vaccine effectiveness.

Perspective of Dr. Jay Bhattacharya

▪Dr. Jay Bhattacharya advocates for randomized clinical trials as the preferred methodology for measuring COVID-19 vaccine effectiveness.
▪Dr. Jay Bhattacharya believes observational methods for calculating COVID-19 vaccine effectiveness are insufficiently rigorous.

Perspective of Former CDC leadership

▪Former CDC leadership views the traditional review process as insulated from political interference across different administrations.
▪Dr. Debra Houry considers political appointee involvement in Morbidity and Mortality Weekly Report decisions to be highly unusual at the CDC.
▪Dr. Debra Houry believes Morbidity and Mortality Weekly Report reviews should be conducted by career scientists rather than political appointees.

Perspective of CDC institutional position

▪The CDC states it remains committed to timely publication of research findings despite the study delay.
▪The CDC defends observational studies as a commonly accepted methodology for measuring vaccine effectiveness.
▪The CDC states it remains committed to transparency in scientific communication despite pausing the vaccine effectiveness study.