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.