Table 2

Mean unadjusted change within individuals in cycle length and menses length, and adjusted difference in the change from three prevaccination cycle average to first or second vaccination cycle and cycle after the second vaccination cycle

Outcome per cycleUnvaccinatedVaccinatedAdjusted difference in change (days; 99.3% CI)*
NoUnadjusted change from prevaccination average (99.3% CI)NoUnadjusted change from prevaccination average (99.3% CI)
Cycle length
 First dose46860.09 (–0.08 to 0.27)14 9360.81 (0.68 to 0.93)0.71 (0.47 to 0.96)
 Second dose44230.21 (0.02 to 0.39)96000.76 (0.60 to 0.93)0.56 (0.28 to 0.84)
 Cycle after second dose41340.20 (0.01 to 0.39)88710.09 (–0.03 to 0.20)–0.11 (–0.33 to 0.10)
Menses length
 First dose4686–0.06 (–0.12 to 0.00)14 5600.01 (–0.02 to 0.04)0.07 (0.00 to 0.13)
 Second dose4423−0.10 (–0.15 to –0.04)90850.03 (–0.01 to 0.07)0.13 (0.06 to 0.20)
  • CI=confidence interval.

  • *Differences between groups come from mixed effects models with random intercepts and slopes at the individual level, an interaction between vaccination status and before and after vaccination timing, and are adjusted for age, body mass index, educational attainment, parity, relationship status, and global region.