DTaP Effectiveness Estimated at 96% During Alaska Pertussis Outbreak

Children aged 6 months to 6 years who had completed the 3-dose primary diphtheria and tetanus toxoids and acellular pertussis vaccine (DTaP) series had markedly lower odds of laboratory-confirmed pertussis than unvaccinated children during a 2024 statewide outbreak in Alaska, according to a report in the CDC's Morbidity and Mortality Weekly Report.

US pertussis incidence increased in 2024 after a low period during and shortly after the COVID-19 pandemic, and the authors noted limited real-world data on DTaP effectiveness during this resurgence. Alaska’s incidence rose from 0.27 cases per 100,000 population in 2022 to a record 83 cases per 100,000 in 2024.

Alaska Department of Health investigators conducted a matched case-control analysis of 84 children with first-time, laboratory-confirmed pertussis and symptom onset from May through November 2024 and 229 control patients with acute cough, matched by birth year and health care facility. Compared with unvaccinated children, adjusted vaccine effectiveness (VE) was 96.2% (95% CI, 89.6%-98.6%) among fully vaccinated children, who had received at least 3 valid DTaP doses at least 2 weeks before specimen collection. Unvaccinated children had approximately 26 times the odds of pertussis compared with fully vaccinated children (adjusted odds ratio [aOR], 26.1; 95% CI, 9.6-70.9).

Adjusted VE was 85.3% (95% CI, 64.4%-94.0%) among partially vaccinated children, who had received 1 or 2 valid doses; these children had higher odds of pertussis than fully vaccinated children (aOR, 3.8; 95% CI, 1.7-8.6). Among fully vaccinated children, time since the most recent dose did not differ significantly between case patients and control patients. The authors cited limitations, including missing symptom-severity data, possible inclusion of control children with untested pertussis, and findings that may not generalize to older children or milder cases.

The authors wrote that declining childhood pertussis vaccination coverage in Alaska might have contributed to the outbreak’s size and that the findings reinforce 2018 Advisory Committee on Immunization Practices recommendations for pertussis vaccination of all infants beginning at age 2 months.

Source: Newell K, Ohlsen E, Moore K, Aho S, Castrodale L, McLaughlin J. Effectiveness of diphtheria and tetanus toxoids and acellular pertussis vaccine in children aged 6 months–6 years during a statewide pertussis outbreak — Alaska, May–November 2024. MMWR Morb Mortal Wkly Rep. 2026;75(40):601-606. doi:10.15585/mmwr.mm7540a1