Effectiveness of Seven and Thirteen Valent Pneumococcal Conjugate Vaccines in a Schedule without a Booster dose: a Ten Year Observational Study.

Background. Unique among high-income countries, Australia has used a 3 + 0 schedule(3 primary doses,no booster)for infant pneumococcal conjugate vaccine(PCV)since January 2005, initially 7 valent (PCV7) then 13 valent (PCV13) from July 2011. We measured vaccine effectiveness(VE)of both PCVs against invasive pneumococcal disease(IPD) using 2 methods. Methods. Cases were IPD notifications to the national surveillance system of children eligible for respective PCVs. For case-control method, up to 10 age-matched controls were derived from the Australian Childhood Immunisation Register. For indirect cohort method, controls were IPD cases due to serotypes not in PCVs. VE was calculated as(1 - odds ratio [OR]) x 100 by logistic regression. VE waning was estimated as odds of vaccine type (VT) IPD in consecutive 12-month periods post-dose 3. Results. Between 2005 and 2014, there were 1209 and 308 IPD cases in PCV7-eligible and PCV13-eligible cohorts, respectively. Both methods gave comparable VE estimates. In infants, VE for 3 doses against VT IPD was 92.9% (95% confidence interval [Cl], 27.7% to 99.3%) for PCV7 and 86.5% (95% Cl, 11.7% to 97.9%) for PCV13. From 12 months post-dose 3, the odds of VT IPD by 24-36 months increased significantly for PCV7(5.6, 95% Cl, 1.2-25.4) and PCV13 (5.9, 95% Cl, 1.0-35.2). Conclusions. For both PCVs in a 3 + 0 schedule, despite similar VE, progressive increase in breakthrough cases only occurred post-PCV13. This supports the importance of a booster dose of PCV 13 in the second year of life lo maintain protection.