More than 28,000 whooping cough cases have been reported across the United States so far in 2026, and California accounts for the largest share of infections. The surge, tracked through weekly federal surveillance tables updated through late June, already exceeds prior peak-year totals at this point in the calendar. Falling childhood vaccination rates in several states are driving the increase, putting infants and other vulnerable groups at heightened risk.
Falling DTaP coverage and a fast-rising case count
The national tally crossed the 28,000 mark in provisional weekly data published by the CDC’s National Notifiable Diseases Surveillance System, last updated June 24, 2026. That system collects reports from every state and territory, applying a standardized case definition that separates confirmed infections from probable ones based on laboratory and clinical criteria. Under the agency’s 2020 pertussis case definition, a confirmed case requires either PCR or culture evidence of Bordetella pertussis, or an epidemiologic link combined with a cough lasting at least two weeks and specific symptoms such as paroxysms, post-tussive vomiting, or whoop.
California’s outsized share of the national count reflects both its large population and conditions that favor sustained transmission. Pertussis tends to cycle in multi-year waves, but the current wave is running well ahead of recent baselines. Crowded schools, uneven booster uptake among adolescents, and pockets of low coverage in certain communities can all create opportunities for the bacterium to circulate. Once pertussis gains a foothold, it can spread quickly through households and classrooms, especially when older children or adults have waning immunity and mild symptoms that go unrecognized.
A key question is whether states that have seen the steepest drops in DTaP booster compliance will ultimately show the tightest correlation with both case volume and outbreak duration. Full line-level data from the national surveillance system would allow researchers to test that relationship directly, but those detailed breakdowns have not yet been released for the current reporting period. For now, health departments are relying on provisional summaries and internal dashboards to track where clusters are forming and which age groups are most affected.
Analysis published by a recent medical review links the U.S. surge explicitly to declining vaccination rates, noting that coverage has dropped in groups that are critical to shielding newborns who are too young for their own shots. Infants under six months bear the highest risk of hospitalization and death from whooping cough, and they depend almost entirely on the immunity of people around them. When community coverage falls below recommended thresholds, the disease can reach babies before they have completed their primary series of doses.
How CDC tracks and classifies pertussis infections
Every case counted toward the 28,000 figure passes through a reporting chain that starts with a clinician or laboratory, moves to a state or local health department, and then flows to the CDC through the National Notifiable Diseases Surveillance System. The agency’s official criteria for pertussis set the bar for what qualifies as a reportable infection. States apply these criteria uniformly, which means the national count reflects a consistent diagnostic standard rather than a patchwork of local rules.
Under that framework, confirmed cases must meet strict laboratory or epidemiologic conditions, while probable cases rely more heavily on clinical presentation and exposure history. Both categories matter for understanding the trajectory of the outbreak, but confirmed infections carry particular weight when officials communicate about trends. Laboratories are encouraged to use PCR testing, which can detect the bacteria early in the course of illness, though culture remains the gold standard in some settings.
The CDC also operates an Enhanced Pertussis Surveillance program through its Active Bacterial Core surveillance network. That program collects deeper epidemiologic and laboratory detail than the standard weekly tables, including information on vaccination status, household contacts, and clinical outcomes. However, it covers a smaller geographic footprint and does not provide real-time case-level data matching the headline threshold. For the broadest national picture, the weekly notifiable disease dataset remains the primary reference.
One critical caveat shapes how readers should interpret the 28,000 figure: all weekly counts in the national notifiable system are provisional. As the CDC’s own interpretation guidance explains, numbers can shift as states finalize reports, reclassify cases, or submit late entries. Some cases initially logged as probable may be upgraded to confirmed, while others may be removed if they fail to meet the definition after further review. The direction of the trend, however, is clear. Early-year totals already exceed comparable windows from prior peak seasons, and the traditional high-transmission months of late summer and fall have not yet arrived.
Gaps in state-level data and vaccination tracking
Several important pieces of the picture are still missing. The publicly available weekly dataset does not yet include finalized state-by-state cumulative totals for the exact week the national count passed 28,000. Without those granular breakdowns, it is difficult to rank states beyond the broad observation that California leads. Researchers and public health officials are waiting for updated extracts that would allow a more precise geographic analysis, including county-level hot spots and age-specific rates.
Equally important, the CDC’s current pertussis surveillance pages do not publish vaccination coverage rates or exemption data alongside case counts. That gap makes it harder to draw a direct, quantified line between falling DTaP uptake in specific jurisdictions and the size or duration of local outbreaks. Annual immunization surveys from the agency’s school-entry and adolescent programs provide some of that information, but those datasets typically lag by months and cover different reporting periods than the weekly disease tables.
The hypothesis that declining booster compliance is the strongest predictor of outbreak severity is plausible on its face and consistent with the medical analysis linking coverage gaps to rising incidence. But proving it at the county or school-district level will require linking two data streams that the federal government does not yet publish in an integrated format. Until that linkage happens, the relationship between vaccine refusal and case clustering will rest on state-level patterns and ecological comparisons rather than precise local evidence.
Local health departments have tried to fill some of these gaps by combining their own immunization registry data with case investigations. In many jurisdictions, investigators ask about vaccination history during contact tracing, then map infections against neighborhoods where school exemptions or delayed schedules are most common. Those efforts can inform targeted outreach, but they are labor-intensive and not standardized nationwide, limiting their value for building a cohesive national picture.
What families can do during the current surge
For parents and caregivers, the practical takeaway is direct. The CDC recommends that children receive five doses of DTaP vaccine by age six, with a Tdap booster in adolescence and additional Tdap doses for adults who have never received one. Pregnant people are advised to get Tdap during each pregnancy, typically in the third trimester, to pass antibodies to the fetus and provide early protection after birth. These measures create layers of defense that can blunt the impact of a pertussis wave even when community transmission is high.
Families can also reduce risk by keeping infants away from people with coughs, encouraging anyone who is ill to stay home from school or work, and seeking medical care promptly if a baby develops spells of intense coughing, pauses in breathing, or difficulty feeding. Clinicians may start antibiotics for suspected pertussis before test results return, particularly in young infants or pregnant patients, to reduce severity and limit spread.
Public health experts stress that the current surge, while serious, is not inevitable in its future scale. Higher vaccination coverage, especially for boosters in older children, teenagers, and adults, can slow transmission and protect those most likely to experience severe disease. As more detailed data emerge over the coming months, they are expected to clarify how closely local coverage patterns track with case counts-and how quickly communities that raise their immunization rates can bend the curve of this year’s outbreak.
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*This article was researched with the help of AI, with human editors creating the final content.
