Opinion: CDC leadership continues to try to manufacture a scientific debate on vaccines where none exists

OpinionFirst Opinion CDC leadership continues to try manufacture a scientific debate on vaccines where none exists A recent seminar on vaccine effectiveness offers a warning Manage alerts for this article Email this article Share this article By Ben LopmanJuly 2, 2026 Lopman is professor of epidemiology and global health at Emory University’s Rollins School of Public Health. What happens if public health agencies stopped trusting their own tools, scientists, and surveillance networks for measuring whether vaccines work? We end up less able to monitor the performance of Covid-19, flu, RSV vaccines, and whatever comes next. That’s the real story behind the recent “Public Health Grand Rounds” — CDC’s flagship seminar series — on the topic of “Measuring Vaccine Effectiveness.”Advertisement While this may seem like an esoteric topic, it sheds light on the ongoing disruption within the agency over vaccine policy. CDC leadership has already blocked publication of its own staff’s study on Covid vaccine effectiveness, citing methodological concerns. And just this week, Health and Human Services posted a new charter for the Advisory Committee on Immunization Practices — the panel that advises CDC on vaccine recommendations — that diminishes its role in evaluating vaccines and instead directs it to assess “alternatives” to vaccination. The methods used to measure whether vaccines work, and the way they were discussed during the recent seminar, are not a side issue. They are squarely in the crosshairs. In his opening remarks, Jay Bhattacharya (who is leading the agency though not officially acting director), framed the series as a reflection of CDC’s renewed commitment to the principles driving scientific progress: excellence, collaboration, transparency, intellectual honesty, and willingness to engage in thoughtful debate on complex issues. Great! The specific topic was how to measure the degree to which vaccines protect people in the real world — so-called vaccine effectiveness studies.Advertisement In fact, the discussion went deeper than that, hinging on a debate about a specific study design. The panel included three scientists with deep expertise in vaccine effectiveness methodology: Carrie Reed, chief of CDC’s Influenza Epidemiology and Prevention Branch; Emily Martin, professor at the University of Michigan; and Natalie Dean, associate professor at Emory University’s Rollins School of Public Health; as well as a representative from HHS leadership, Martin Kulldorff, chief science officer for the Office of the Assistant Secretary for Planning and Evaluation. Reed and Martin presented, in depth, the principles of real-world vaccine studies and the methods underlying them. They laid out the fundamentals of the study designs, the reasons we use them, the real-world questions they have answered, the policy decisions they have informed, and, critically, their limitations, as well as the decades of work that have gone into examining how significant those limitations are and what can be done to address them. While there are many approaches to estimating vaccine effectiveness, the test-negative design, or TND, is the mainstay. It’s a form of a case-control study, where you compare people who had a disease (cases) to those who didn’t (controls). The innovation of the TND is that cases and controls are identified based on whether they test positive or negative for a particular vaccine-preventable pathogen. For example, if you’re hospitalized with a severe respiratory infection and test positive for flu, you’re a case. If you test negative, you’re a control. Then you look at whether those people were vaccinated. If the vaccine is working, cases will be less likely to have been vaccinated than controls. It’s an elegant solution to a real-world problem. It’s fast, inexpensive, and widely used. Of course, it’s not perfect, which is precisely why the scientific community has spent years working to validate and improve it. That’s how applied science works.Advertisement Kulldorff claimed on the Grand Rounds to have identified “the fatal flaw in test-negative designs.” One of his stated fatal flaws was that you can’t use this approach when cases and controls have different diseases — you shouldn’t use it to compare risk factors for pancreatic versus lung cancer, for example. To which the response of the other panelists — and, I’m imagining, my entire field watching the webcast — was essentially: Of course, and that’s why we don’t. The TND relies on people seeking care for the same illness, like symptoms of a respiratory infection. They don’t seek care for a specific pathogen. But as Dean pointed out, vaccines prevent specific pathogens: Covid vaccines prevent SARS-CoV-2, but not RSV or flu — and that’s precisely why the design works. So why does any of this matter? It matters on two levels. First, practically: If the TND is discredited or sidelined, we lose one of our primary tools for monitoring vaccine performance in real time. This is the kind of ongoing surveillance analysis that tells us whether this season’s flu shot is working or if a new vaccine, like for RSV, is performing as expected. Second, politically: Bhattacharya has already blocked publication of a CDC study on Covid vaccines, citing “concerns regarding the methodological approach to estimating vaccine effectiveness.” (Notably, the paper was ultimately published in a peer-reviewed journal.) Others have written extensively about the inconsistency and lack of logic in that decision, so I won’t here. More broadly, Kulldorff, Bhattacharya, and other appointees in Robert F. Kennedy Jr.’s HHS have raised persistent doubts about Covid vaccines and about vaccine science more generally. What happened at the Grand Rounds appeared to be an attempt to manufacture a scientific debate where, in reality, there isn’t one. The TND works quite well. Some of the world’s foremost experts in TND and vaccine evaluation are at the CDC. They have innovated impressively with the constraints and resources and data available to them, and they constantly work to validate and improve their methods. Any open-minded observer would have come away from the discussion reassured that these scientists and the broader network of investigators who seek to answer questions about vaccine performance in the real world are rigorous, creative, and methodical.Advertisement Bhattacharya’s closing remarks included the platitudes: “We owe each other this kind of discussion” and “we owe the public the very best regarding the truth.” However, a more pointed truth emerged from the recent discussion: We have robust tools for evaluating vaccines in the real world and a community of committed scientists who dispassionately do the work. They don’t claim their methods are perfect; they’ve spent careers proving they aren’t, and improving them anyway, and they will continue to do so. The question now is whether the institutions that depend on that work will trust it. Ben Lopman is professor of epidemiology and global health at Emory University’s Rollins School of Public Health. 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