CDC Report Shows DTaP Vaccine Reduced Pertussis Risk in Alaska Outbreak

What was announced

The CDC Morbidity and Mortality Weekly Report detailed a matched case-control study tracking young children in Alaska between May and November 2024. A case-control study compares individuals with a disease to similar individuals without it to find patterns in past exposures or treatments.

State records identified 113 laboratory-confirmed pertussis cases in children aged six months to six years. Researchers matched 84 of these children with 229 control patients who had cough symptoms but tested negative or were not tested for pertussis.

Among fully vaccinated participants who had received at least three valid DTaP doses, vaccine effectiveness was 96.2 percent. For partially vaccinated children who had one or two doses, vaccine effectiveness was 85.3 percent. Unvaccinated children had 26.1 times the odds of developing laboratory-confirmed pertussis compared to fully vaccinated children. Children with one or two doses had 3.8 times the odds of disease compared to those with three or more doses.

What it means

Pertussis is a respiratory bacterial infection that spreads easily between people. Vaccine coverage among young children in Alaska had fallen below national averages before the 2024 outbreak, while statewide incidence jumped from 0.27 cases per 100,000 people in 2022 to 83 cases per 100,000 in 2024.

The data indicates that completing the initial three-dose DTaP series gave young children substantial protection during a period of heavy transmission. Partial vaccination offered lower protection than the full primary series, but still lowered risks relative to receiving no doses.

Matching study participants by health facility helped researchers account for differences in local healthcare access and diagnostic habits across Alaska.

What the announcement does not tell us

The report does not provide details on symptom severity or medical outcomes like hospital stays and deaths. Surveillance systems did not collect data regarding how sick each child became.

It does not explain why pertussis cases spiked so sharply across Alaska in 2024 beyond noting potential factors like waning immunity and lower vaccination rates.

Additionally, the analysis excluded 29 infected children because they lacked matched controls at their facility or were born outside the state. The authors noted that children with mild symptoms who never sought medical care were not captured in the study.