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]) × 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 [CI], 27.7% to 99.3%) for PCV7 and 86.5% (95% CI, 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% CI, 1.2-25.4) and PCV13 (5.9, 95% CI, 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 PCV13 in the second year of life to maintain protection.