Effectiveness of Pneumococcal Conjugate Vaccine Using a 2+1 Infant Schedule in Quebec, Canada

Background: In the province of Quebec, Canada, pneumococcal conjugate vaccine (PCV) is offered to all children aged less than 5 years, and a 2 + 1 schedule (2, 4, and 12 months) is recommended for low-risk infants, with other schedules including a lower number of doses for older children. Objective: To estimate PCV effectiveness against invasive pneumococcal disease (IPD). Methods: IPD cases in children aged 2-59 months and reported during the years 2005-2007 were eligible and uninfected controls were randomly identified in the provincial health insurance registry. Parents were interviewed by telephone and immunization records were reviewed. The PCV effectiveness was computed using unconditional logistic regression models adjusting for potential confounders. Results: 180 IPD cases (60.4% of total reported) and 897 controls were included. Predictors of IPD risk were age, season, high-risk medical conditions, day-care attendance, and low family income. Overall PCV protection (>1 dose) against IPD caused by any serotype was 60% (95% CI: 38%-75%), and was 92% (83%-96%) against IPD caused by vaccine serotypes. Among low-risk children who received the recommended 2 + 1 schedule, 6 cases of vaccine failure occurred after the first dose, 1 case after the second dose, and no cases after the booster dose. Conclusion: These results confirm the effectiveness of PCV after 2 and 3 doses.