DTaP shots were 96% effective in Alaska's 2024 pertussis outbreak, CDC finds

Three or more doses of the childhood DTaP vaccine were 96.2% effective at preventing pertussis in young children during a statewide whooping-cough outbreak in Alaska, the U.S. Centers for Disease Control and Prevention reported on 15 October 2026 [s1]. The estimate, from a matched case-control study, carried a 95% confidence interval of 89.6% to 98.6% [s1].

Between 1 May and 30 November 2024, Alaska reported 113 laboratory-confirmed pertussis cases among children aged 6 months to 6 years — an incidence of 193.0 per 100,000 children in that age group [s1]. Statewide pertussis incidence across all ages reached 83 per 100,000 population in 2024, a record high for the state [s1].

How the study was done

Researchers ran a matched case-control analysis, the standard design for measuring vaccine effectiveness in an outbreak. From the 113 cases, seven were excluded because the children were born outside Alaska and 22 because no age-matched control was available at the reporting facility, leaving 84 case-patients [s1]. These were matched to 229 control patients — children with acute cough who were tested and either negative for pertussis or not tested for it — drawn from 17 facilities, about 2.7 controls per case [s1]. The median age was 2.2 years [s1]. Models compared vaccinated children with unvaccinated children and were adjusted for race, sex and calendar month [s1].

The contrast in vaccination status was stark. Among cases, 52 (61.9%) were unvaccinated, compared with 28 (12.2%) of controls [s1]. Conversely, 177 of the controls (77.3%) had received three or more valid DTaP doses, against just 21 of the cases (25.0%) [s1]. Translated into odds, unvaccinated children had 26.1 times the odds of pertussis compared with fully vaccinated children, with a 95% confidence interval of 9.6 to 70.9 [s1]. A further 11 cases (13.1%) and 24 controls (10.5%) were partially vaccinated [s1]. The size of the unadjusted and adjusted estimates was similar, which suggests the measured protection was not an artefact of the factors the researchers controlled for.

Partial vaccination still helped

Children who had received only one or two doses were not left unprotected. Adjusted effectiveness for partial vaccination was 85.3%, with a wide confidence interval of 64.4% to 94.0% reflecting the small number of such children [s1]. The gradient — higher protection with more doses — is what the multi-dose DTaP schedule is designed to produce, and it argues for completing the series rather than treating one or two shots as sufficient.

The analysis also looked at whether protection faded with time since the last dose. Among fully vaccinated children, the median interval since the last DTaP dose was 15.3 months for cases and 10.2 months for controls, a difference that was not statistically significant (p = 0.23) [s1]. In other words, this outbreak did not show clear evidence of waning within the age range studied, though the authors note the sample was too small to analyse effectiveness by specific number of doses [s1].

What it does and does not show

The findings sit squarely within what is already known: acellular pertussis vaccines are highly protective in the first years after a child completes the series, even if protection is understood to wane over the longer term into adolescence. What this report adds is a clean, recent, real-world estimate from an active outbreak, where the stakes of under-vaccination are concrete rather than hypothetical.

The study has limits the authors are explicit about. It did not collect data on illness severity, hospitalisation or deaths, so it speaks to whether vaccinated children caught pertussis, not to how sick they became [s1]. Control children were identified through cough testing rather than a general population sample, and the small number of partially vaccinated children makes that estimate imprecise [s1]. The case-control design also cannot by itself explain why an outbreak of this size occurred.

Pertussis is cyclical and resurgent in several high-income countries, and outbreaks concentrate harm in the youngest children, for whom the disease is most dangerous. The practical reading of the Alaska data is narrow and firm: during this outbreak, children who had completed their DTaP doses were far less likely to be among the confirmed cases than children who had not.

This article is informational and is not medical advice.