Table 2:

Crude and adjusted estimates of vaccine effectiveness, including sensitivity analyses*

Variable; time since last vaccinationPertussis positive, no. vaccinated/totalPertussis negative, no. vaccinated/totalCrude vaccine effectiveness, % (95% CI)Adjusted vaccine effectiveness, % (95% CI)
Up-to-date vaccination
 15–364 d54/2131691/247684 (78 to 89)§80 (71 to 86)§
 1–3 yr46/2051089/187479 (71 to 85)§84 (77 to 89)§
 4–7 yr51/210391/117636 (10 to 54)§62 (42 to 75)§
 ≥ 8 yr42/201213/9983 (−41 to 33)41 (0 to 66)
Partial vaccination
 15–364 d13/172340/112581 (66 to 89)§75 (54–86)§
 1–3 yr27/186344/112961 (41 to 75)§68 (50 to 80)§
 4–7 yr30/189223/100834 (−1 to 56)56 (30 to 72)§
 ≥ 8 yr64/223305/1090−4 (−43 to 25)36 (−6 to 61)
Sensitivity analyses for participants with up-to-date vaccination compared with unvaccinated participants
Exposure misclassification
 15–364 d54/2131691/247696 (89 to 100)§95 (87 to 100)§
 1–3 yr46/2051089/187498 (93 to 100)§98 (94 to 100)§
 4–7 yr51/210391/117656 (27 to 80)§63 (35 to 82)§
 ≥ 8 yr42/201213/99814 (−61 to 67)22 (−70 to 73)
Excluding infants aged < 7 mo with incomplete primary series
 15–364 d26/1581192/176191 (86 to 94)§87 (79 to 92)§
 1–3 yr46/1781089/165882 (74 to 87)§84 (77 to 89)§
 4–7 yr51/183391/96044 (20 to 60)§62 (42 to 75)§
 ≥ 8 yr42/174213/78215 (−24 to 42)42 (0 to 66)
Indeterminate pertussis PCR considered positive
 15–364 d105/3051691/427676 (69 to 81)§71 (61 to 79)§
 1–3 yr82/2821089/187470 (61 to 78)§79 (72 to 85)§
 4–7 yr68/268391/117632 (8 to 50)§62 (45 to 74)§
 ≥ 8 yr59/259213/9980 (−9 to 24)41 (5 to 63)§
Indeterminate pertussis PCR considered negative
 15–364 d54/2131742/256884 (78 to 88)§80 (53 to 86)§
 1–3 yr46/2051125/195179 (70 to 85)§83 (76 to 89)§
 4–7 yr51/210408/123435 (9 to 54)§59 (37 to 73)§
 ≥ 8 yr42/201230/10565 (−37 to 35)37 (−7 to 63)
Restricted to years 2009–2011
 15–364 d22/53839/114474 (55 to 85)§71 (43 to 85)§
 1–3 yr13/44455/76072 (45 to 86)§84 (65 to 92)§
 4–7 yr11/42144/44925 (−54 to 63)70 (26 to 87)§
 ≥ 8 yr4/3561/36628 (−70 to 69)79 (28 to 94)§
Restricted to years 2012–2013
 15–364 d32/160852/133286 (79 to 91)§83 (73 to 89)§
 1–3 yr33/161634/111481 (71 to 87)§85 (76 to 90)§
 4–7 yr40/168247/72739 (4 to 62)§57 (29 to 73)§
 ≥ 8 yr38/166152/6326 (−41 to 38)24 (−38 to 51)
Excluding outbreak
 15–364 d48/1391578/225078 (68 to 84)§76 (63 to 84)§
 1–3 yr38/129974/164671 (57 to 81)§82 (72 to 88)§
 4–7 yr34/125342/101427 (−12 to 52)§65 (41 to 79)§
 ≥ 8 yr25/116183/855−1 (−62 to 37)55 (13 to 77)§
  • Note: CI = confidence interval, PCR = polymerase chain reaction.

  • * Reference group was the unvaccinated population.

  • Adjusted for age, sex, rural v. urban residence, income quintile, any comorbidity, ambulatory health care use in previous 12 months, emergency health care use in previous 12 months and inpatient health care use in previous 12 months.

  • Additional details in Appendix 2, available at www.cmaj.ca/lookup/suppl/doi:10.1503/cmaj.160193/-/DC1.

  • § p < 0.05.

  • The variable “any comorbidity” was excluded from these models owing to quasi-separation of data points.