Table 1.

Characteristics of the study population.

	All children	Infected before vaccination	Not infected before vaccination
N	64	30	34
Age (mean(sd))	12 (3)	10 (3)	13 (2)
Sex (N female (%female))	39 (61)	22 (73)	17 (50)
1 vaccine / 2 vaccines (N)	18/28	18/12	0/34
Vaccine Interval (median days (range))	28 (21-81)	56 (21 - 81)	28 (21-60)
Paired samples before first vaccination and after first vaccination available (N)	44	30	14
Paired samples before second vaccination and after second vaccination available (N)	43	9	34

sd, standard deviation.