Every winter since the first COVID-19 vaccines rolled out, the Centers for Disease Control and Prevention has published interim estimates showing how well the latest shots protect against severe illness. Doctors use those numbers to counsel patients. Advisory panels use them to shape national recommendations. And millions of Americans use them, directly or indirectly, to decide whether to roll up their sleeves.
This season, that data has not appeared. The CDC has delayed its anticipated report on 2025-26 COVID-19 vaccine effectiveness, the Washington Post reported in April 2026. The agency has not publicly explained the holdup, and no revised publication timeline has been announced. The result is an unusual silence at a moment when updated evidence would normally be guiding clinical decisions across the country.
What the CDC has published – and what it hasn’t
The CDC’s track record on this front is well established. Each respiratory season, the agency’s researchers use a test-negative case-control design – comparing outcomes among vaccinated and unvaccinated people who seek care for respiratory symptoms – to estimate how much protection the current vaccines provide. Those findings are published in the agency’s Morbidity and Mortality Weekly Report (MMWR), typically during the winter months when hospitalizations peak.
That pipeline has kept running for influenza. A March 2026 MMWR report delivered interim flu vaccine effectiveness estimates for the 2025-26 season covering September 2025 through February 2026, broken down by age group and severity of illness. The surveillance networks behind that report, including the multi-state VISION collaboration, are the same ones used to track COVID-19 vaccine performance.
For COVID-19, the most recent published estimates cover the prior season. A 2024-25 MMWR report assessed vaccine effectiveness in adults 18 and older, drawing on the VISION network for emergency department and urgent care visits and both VISION and IVY networks for hospitalizations. That analysis found that receiving the season’s updated dose reduced the risk of serious COVID-19 illness compared with remaining unvaccinated or relying on earlier formulations. The report did not provide a single headline effectiveness percentage; instead it presented estimates stratified by outcome type, time since vaccination, and network, making a simple summary figure impractical without flattening important nuance. A separate pediatric analysis, using the same methodology and electronic health records from late August 2024 through early September 2025, showed that updated doses offered added protection for children and adolescents as well.
The VISION network itself remains active. The collaboration between the CDC, Westat, and multiple health systems integrates electronic health records, lab results, pharmacy data, and immunization registries to monitor real-world vaccine performance across diverse populations. Its continued output on the flu side confirms the infrastructure is functioning. The question is why the COVID-19 side has gone quiet.
Why the delay matters – and the political backdrop
Vaccine effectiveness estimates are not academic exercises. They feed directly into the CDC’s Advisory Committee on Immunization Practices (ACIP), which uses them to evaluate whether current recommendations should be adjusted, expanded, or narrowed. When ACIP reviewed the 2024-25 COVID-19 vaccines, MMWR data was central to its evidence-to-recommendations framework. Without a comparable report for the current season, the committee and the clinicians who follow its guidance are working with older numbers.
The delay arrives during a period of significant upheaval at the Department of Health and Human Services. The current administration has pursued sweeping leadership changes at HHS and the CDC, along with substantial budget and staffing reductions that have affected multiple agency programs. Those shifts have raised questions among public health observers about whether the CDC’s capacity or willingness to publish findings that support vaccination has been affected. The Washington Post’s reporting references internal agency dynamics, but neither the CDC nor HHS has confirmed that political or budgetary pressures played a role in the delayed report. Without an official explanation, the political context remains relevant background rather than established cause.
The timing is particularly sensitive because the FDA authorized updated mRNA COVID-19 vaccines from both Pfizer and Moderna ahead of the 2025-26 season. (The FDA’s authorization announcements for the updated formulations have not been linked here because no specific URL was provided in the original sourcing; readers can find them on the FDA’s website.) Post-market effectiveness data would show whether those reformulated shots match the variants currently circulating and whether protection holds across age groups and risk categories. That information matters most to the people at greatest risk of severe outcomes: older adults, those with chronic conditions, pregnant individuals, and immunocompromised patients.
The delay also creates a communication vacuum. In previous seasons, the CDC’s interim reports served as an anchor for public health messaging, giving physicians and health departments concrete numbers to share with a public that has grown increasingly skeptical of vaccine guidance. Without fresh data, that vacuum can fill with speculation or outdated claims from less reliable sources.
What we don’t know
The CDC has not issued a public statement explaining the delay through any MMWR entry or official channel available as of May 2026. The Washington Post attributed the holdup to internal agency dynamics, but no institutional record confirms a specific cause or a new target date for publication.
Several plausible explanations exist, though none has been confirmed. New variants could be complicating the analysis if breakthrough infection patterns have shifted. Widespread hybrid immunity from prior infections and vaccinations may be making it harder to isolate the effect of the current season’s dose. Staffing constraints or changes in the agency’s internal review process could also be factors. The contrast with the on-schedule flu report suggests the issue is specific to the COVID-19 data stream rather than a wholesale breakdown in the CDC’s surveillance capacity, but that remains an inference, not a confirmed fact.
It is also unclear whether draft 2025-26 COVID-19 effectiveness data exists within the agency. If preliminary numbers have been generated but not cleared for publication, the delay may reflect disagreements over interpretation, messaging, or timing rather than a gap in the underlying science.
What the existing evidence still tells us
For people making vaccination decisions now, the 2024-25 effectiveness data remains the most recent benchmark. Those estimates, built on the same networks and analytic methods that would underpin the delayed 2025-26 report, showed measurable protection against emergency visits and hospitalizations in both adults and children. Across multiple prior seasons, the pattern has been consistent: updated COVID-19 vaccines reduce the risk of severe illness, even when they do not prevent all infections.
That track record does not guarantee identical results against whatever variants dominate this season. But it does provide a reasonable basis for clinical conversations, especially for higher-risk individuals weighing whether to act now or wait for numbers that may not arrive soon. Discussing personal risk factors, local transmission trends, and prior vaccination or infection history with a physician remains the most practical path forward.
A note on sourcing
Readers should be aware that this article is built primarily on two categories of sources: CDC MMWR publications, which carry high credibility because they undergo internal agency review and describe reproducible methods, and the Washington Post’s reporting on the delay, which relies on journalistic sourcing rather than official CDC documentation. This article does not include original interviews with CDC officials, independent public health experts, or clinicians. The absence of those voices is a limitation. The specific reasons for the delay and any internal deliberations remain secondhand until the CDC addresses them publicly or independent reporting surfaces additional detail.
The broader lesson is one of institutional transparency. The CDC’s MMWR reports have become a cornerstone of how the public and the medical community evaluate vaccine performance in real time. When that cornerstone is missing without explanation, it strains the trust the agency needs to maintain. A clear public statement about the timeline, the analytic challenges involved, and any interim findings would go further toward preserving confidence than silence, even if the final numbers are not yet ready.
Until the 2025-26 report is released, the evidence already in hand points in a familiar direction: updated vaccines have consistently offered meaningful protection against the worst outcomes of COVID-19. The delayed report will eventually clarify how that protection holds up against the latest variants. In the meantime, the data from prior seasons, and the clinical judgment of individual physicians, remain the best tools available.
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*This article was researched with the help of AI, with human editors creating the final content.
