BACKGROUND Acellular pertussis vaccines replaced whole-cell vaccines for the 5-dose childhood vaccination series in 1997. A sixth dose of pertussis-containing vaccine, tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis, adsorbed (Tdap), was recommended in 2005 for adolescents and adults. Studies examining Tdap vaccine effectiveness (VE) among adolescents who have received all acellular vaccines are limited. METHODS To assess Tdap VE and duration of protection, we conducted a matched case-control study during the 2012 pertussis epidemic in Washington among adolescents born during 1993–2000. All pertussis cases reported from January 1 through June 30, 2012, in 7 counties were included; 3 controls were matched by primary provider clinic and birth year to each case. Vaccination histories were obtained through medical records, the state immunization registry, and parent interviews. Participants were classified by type of pertussis vaccine received on the basis of birth year: a mix of whole-cell and acellular vaccines (1993–1997) or all acellular vaccines (1998–2000). We used conditional logistic regression to calculate odds ratios comparing Tdap receipt between cases and controls. RESULTS Among adolescents who received all acellular vaccines (450 cases, 1246 controls), overall Tdap VE was 63.9% (95% confidence interval [CI]: 50% to 74%). VE within 1 year of vaccination was 73% (95% CI: 60% to 82%). At 2 to 4 years postvaccination, VE declined to 34% (95% CI: −0.03% to 58%). CONCLUSIONS Tdap protection wanes within 2 to 4 years. Lack of long-term protection after vaccination is likely contributing to increases in pertussis among adolescents.

Overall, non-food exposures were as important as food-related exposures with regard to their contributions to the proportion of cases. Infection prevention efforts should address kitchen hygiene practices and non-food exposures, such as recreational water exposure, in addition to food-consumption risks.

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A comparison of sex differential mortality rates indicates that women are at increased risk in several countries of Asia, in part due to less access to a variety of services and lower priority for food than their male siblings. Poorer nutritional status becomes apparent during adolescence, with a delay in maturation which may have repercussions for subsequent ability of the biologically immature woman to carry through a normal pregnancy. There is a dearth of information on girls during this vulnerable period of life which is recently being corrected by studies in Nepal, India and the Philippines where the magnitude of dietary risk is being compared with its impact on nutritional status and the sociocultural factors that may be responsible.