Background: The Wyeth heptavalent CRM-197 pneumococcal conjugate vaccine (PCV) was found to be 97.4% effective against invasive pneumococcal disease in 37,868 children within Northern California Kaiser Permanente. An intent-to-treat analysis of effectiveness against acute otitis media (AOM) found a 7.1% reduction in AOM office visits.
Objective: To assess the effectiveness of PCV against AOM by age, season of the year, and frequency of AOM.
Design/Methods: Randomized double blind trial (PCV vs. active placebo) with follow-up from randomization (mean age: 2.1 months) through April 1999 (mean age: 2.3 years, range: 0.9 - 3.7). Effectiveness was examined using Cox regression for multiple events with robust variance estimation.
Results: There were 3.3 AOM visits per child, with incidence highest at ages 8-11 months. By age group, the percent of AOM visits prevented by PCV was: 4.0% (2-7 mths), 7.8% (8-11 mths), 7.9% (12-14 mths), 11.1% (15-17 mths), 7.1% (18-23 mths), 4.6% (24-30 mths), and 5.6% (30-42 mths). The 11.1% effectiveness at 15-17 months, soon after the booster dose, was significantly higher than was found before 7 months or after 24 months (p < .05). Effectiveness did not vary by season. The PCV group received 24.9% fewer tympanostomy tube procedures than the control group. PCV reduced by 11.0% the risk of 5 visits, by 14.7% the risk of 10 visits, and by 15.4% the risk of 15 visits.
Conclusions: The effectiveness of PCV against AOM is highest at age 15-17 months and unrelated to season. Effectiveness is highest against frequent AOM.