Vaccine effectiveness by week of vaccination calculated by the case-series method.

Results are given for different lengths of the unprotected period (9 vs 11 days, respectively; first column); for all ages, those aged less than 14 years and 14 years and above (third column); and when the number of total cases exercising force of infection excludes (lower half) or includes (upper half) reported cases with unknown vaccination status. Cells are empty for weeks where no vaccinated case was reported neither in the unprotected nor in the protected period; pv = post vaccination; up = unprotected period; pp = protected period; VE = vaccine effectiveness; CL = confidence limit.