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.
dAlthough pertussis disease is vaccine preventable, Washington State experienced a substantial rise in pertussis incidence beginning in 2011. By June 2012, the reported cases reached 2,520 (37.5 cases per 100,000 residents), a 1,300% increase compared with the same period in 2011. We assessed the molecular epidemiology of this statewide epidemic using 240 isolates collected from case patients reported from 19 of 39 Washington counties during 2012 to 2013. The typing methods included pulsed-field gel electrophoresis (PFGE), multilocus variable number tandem repeat analysis (MLVA), multilocus sequence typing (MLST), and pertactin gene (prn) mutational analysis. Using the scheme PFGE-MLVA-MLST-prn mutations-Prn deficiency, the 240 isolates comprised 65 distinct typing profiles. Thirty-one PFGE types were found, with the most common types, CDC013 (n ؍ 51), CDC237 (n ؍ 44), and CDC002 (n ؍ 42), accounting for 57% of them. Eleven MLVA types were observed, mainly comprising type 27 (n ؍ 183, 76%). Seven MLST types were identified, with the majority of the isolates typing as prn2-ptxP3-ptxA1-fim3-1 (n ؍ 157, 65%). Four different prn mutations accounted for the 76% of isolates exhibiting pertactin deficiency. PFGE provided the highest discriminatory power (D ؍ 0.87) and was found to be a more powerful typing method than MLVA and MLST combined (D ؍ 0.67). This study provides evidence for the continued predominance of MLVA 27 and prn2-ptxP3-ptxA1 alleles, along with the reemergence of the fim3-1 allele. Our results indicate that the Bordetella pertussis population causing this epidemic was diverse, with a few molecular types predominating. The PFGE, MLVA, and MLST profiles were consistent with the predominate types circulating in the United States and other countries. For prn, several mutations were present in multiple molecular types.
Policy-makers require information on the potential benefits of and economic case for pneumococcal conjugate vaccination in middle-income countries. We built decision analysis models to evaluate a three-dose infant series of the 7-, 10- or 13-valent pneumococcal conjugate vaccines in 77 middle-income countries compared with no vaccination, accounting for direct protection of vaccinated children as well as herd protection and serotype replacement in unvaccinated children and adults. Over 10 years, pneumococcal vaccination would prevent at least 11.0 million cases and 314 000 deaths in children under-5, one-third of the pneumonia and invasive disease cases and deaths that would occur in this age group without vaccination. Herd protection would prevent 3.1 million cases and 163 000 deaths in older children and adults. A total of 11.1 million discounted disability-adjusted life-years (DALY) would be averted. At a dose cost of $10 for lower- middle-income and $20 for upper-middle-income countries, the net pooled (for all countries together) discounted vaccination cost would be $18.1 billion ($1600 per DALY averted). Vaccination would be cost effective for 72 countries with the 7-valent vaccine and for all countries with the 10- or 13-valent vaccines. The economic case for vaccination is compelling for middle-income countries.
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