Table 2.

Percentage of P.69 types isolated from different age groupsa

Age group (mo)No. of strainsVaccine-induced immunityb% of P.69 types isolatedc
Vaccine type (P.69A)Non-vaccine types (P.69B and P.69C)
0–355No2278
4–1135Partial1189
12–4840Optimal893
>4867Waning1882
 Total1971684
  • a Data are from the years 1989 to 1996.

  • b Estimation of the level of vaccine-induced immunity was based on the fact that in The Netherlands, children are vaccinated at 3, 4, 5, and 11 months of age. Further, vaccine-induced immunity is known to wane after a few years.

  • c Percentages were calculated within each age group. The downward trend observed in the percentage of vaccine type P.69 in the categories with no, partial, and optimal vaccine-induced immunity was significant (P = 0.024), and the upward trend observed in the categories with optimal and waning immunity was marginally significant (P = 0.066).