Table 3.
Influenza Vaccine Effectiveness Against Influenza A(H3N2), Canadian Sentinel Practitioner Surveillance Network 2016–2017 and 2017–2018
| 2016–2017 | 2017–2018 | |||||||
|---|---|---|---|---|---|---|---|---|
| Model and Covariates | A(H3N2) Cases n vac/ N Total (%) | Influenza Test- Negative Controls n vac/ N Total (%) | Unadjusted VE % (95% CI) | Adjusteda VE% (95% CI) | A(H3N2) Cases n vac/ N Total (%) | Influenza Test-Negative Controls n vac/ N Total (%) | Unadjusted VE % (95% CI) | Adjusteda VE % (95% CI) |
| Overall (age,b province,c interval,d calendar timee) | 163/684 (24) | 416/1256 (33) | 37 (22–49) | 36 (18–50) | 201/639 (31) | 596/1719 (35) | 14 (−5 to 29) | 14 (−8 to 31) |
| + Comorbidityb-f | 148/624 (24) | 392/1163 (34) | 39 (24–51) | 36 (17–50) | 197/611 (32) | 572/1642 (35) | 11 (−8 to 27) | 9 (–14 to 27) |
| + Comorbidity and sexb-f,g | 148/621 (24) | 392/1159 (34) | 39 (24−51) | 35 (16−50) | 195/605 (32) | 569/1627 (35) | 12 (–8 to 27) | 10 (−13 to 28) |
| Restricted by age subset | ||||||||
| 1–19 yearsc-e,h | 26/201 (13) | 57/309 (18) | 34 (−9 to 60) | 12 (−53 to 49) | 21/124 (17) | 65/336 (19) | 15 (−46 to 51) | −21 (−116 to 33) |
| 20–64 yearsc-e,i | 84/386 (22) | 240/770 (31) | 39 (18–54) | 41 (19–56) | 109/404 (27) | 353/1133 (31) | 18 (−5 to 37) | 15 (−12 to 35) |
| ≥ 65 yearsc-e | 53/97 (55) | 119/177 (67) | 41 (2–65) | 40 (−8 to 67) | 71/111 (64) | 178/250 (71) | 28 (−15 to 55) | 25 (−24 to 55) |
| Restricted by province | ||||||||
| Albertab,d,e | 27/136 (20) | 109/301 (36) | 56 (29–73) | 55 (22–74) | 48/159 (30) | 163/429 (38) | 29 (−4 to 52) | 43 (10–64) |
| British Columbiab,d,e | 62/212 (29) | 147/427 (34) | 21 (−13 to 45) | 23 (−19 to 50) | 24/70 (34) | 149/442 (34) | −3 (−75 to 40) | 5 (−70 to 47) |
| Ontariob,d,e | 49/195 (25) | 126/329 (38) | 46 (20–63) | 38 (1–62) | 100/236 (42) | 227/566 (40) | −10 (−49 to 19) | −11 (−56 to 21) |
| Quebecb,d,e | 25/141 (18) | 34/199 (17) | −5 (−85 to 41) | 22 (−50 to 59) | 29/174 (17) | 57/282 (20) | 21 (−29 to 52) | 18 (−46–54) |
| Restricted by epidemic period | ||||||||
| November/Decemberb-d | 35/183 (19) | 83/332 (25) | 29 (−11 to 55) | 42 (5–65) | 52/162 (32) | 129/396 (33) | 2 (−45 to 34) | 26 (−17 to 54) |
| January/Februaryb-d | 113/450 (25) | 211/610 (35) | 37 (17–52) | 30 (5–48) | 122/419 (29) | 311/900 (35) | 22 (0–40) | 15 (−12 to 36) |
| March/Aprilb-d | 15/51 (29) | 122/314 (39) | 34 (−25 to 66) | 18 (−73 to 61) | 27/58 (47) | 156/423 (37) | −49 (−159 to 14) | −20 (−129 to 37) |
Abbreviation: CI, confidence interval; n vac, number vaccinated; VE, vaccine effectiveness.
aAll estimates displayed were additionally assessed using Firth’s penalized logistic regression [30–32] but remained within 1% (absolute) in 2016–2017 and within 3% (absolute) in 2017–2018.
bAdjusted for age group specified as: 1–8, 9–19, 20–49, 50–64, ≥ 65 years.
cAdjusted for province specified as: Alberta, British Columbia, Ontario, Quebec.
dAdjusted for specimen collection interval specified as ≤4 days, 5–7 days.
eAdjusted for calendar time based on week of specimen collection modeled using natural cubic spline function with 3 equally spaced knots.
fAdditionally adjusted for comorbidity specified as yes or no (excluding those with missing information) for any chronic conditions that Canada’s National Advisory Committee on Immunization has indicated place individuals at higher risk of serious complications from influenza including: heart, pulmonary (including asthma), renal, metabolic (such as diabetes), blood, cancer, or immune comprising conditions; conditions that compromise management of respiratory secretions and increase risk of aspiration; or morbid obesity (body mass index ≥ 40).
gAdditionally adjusted for sex as male or female, excluding those with missing information.
hAdjusted for age group specified as: 1–8, 9–19 years.
iAdjusted for age group as 20–49, 50–64 years.