Table 3.
Number and percentage of influenza virus positive (Flu +) illnesses among children aged 2–8 years by vaccine exposure category and estimates of influenza vaccine effectiveness (VE) against all influenza A and B viruses in each season and against A(H3N2) viruses only and against B influenza viruses only during the combined 2011–12 and 2012–13 seasons
| Season 2011–12 - All Viruses | Season 2012–13 - All Viruses | Seasons 2011–12 and 2012–13- A[H3N2] onlya | Season 2012–13 - B viruses onlyb | ||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Adjustedc | Adjustedc | Adjustedc | Adjustedc | ||||||||||||||||||||||||||
| Total | Flu + |
(Row % |
% | ) | VE | (95% CI) |
Total | Flu + c |
(Row % |
% | ) | VE | (95% CI) |
Totalb | H3 Flu + |
(Row % |
% | ) | VE | (95% CI) |
Totala | Flu B+ |
(Row % |
% | ) | VE | (95% CI) |
||
| Current Season Dose of IIV3 Regardless of Priming for Ages 2–8 Years Old | |||||||||||||||||||||||||||||
| Unvaccinated (REF) | 633 | 128 | ( | 20 | ) | REF | 654 | 332 | ( | 51 | ) | REF | 1051 | 224 | ( | 21 | ) | REF | 516 | 194 | ( | 38 | ) | REF | |||||
| One or more doses | 458 | 46 | ( | 10 | ) | 47 |
(22– 65) |
394 | 123 | ( | 31 | ) | 49 |
(32– 62) |
773 | 90 | ( | 12 | ) | 47 |
(28– 60) |
338 | 67 | ( | 20 | ) | 53 |
(32– 68) |
|
| Alternative Definitions of Priming for Ages 2–8 Years Old | |||||||||||||||||||||||||||||
| Priming: ≥1 doses of any influenza vaccine in prior season onlyd | |||||||||||||||||||||||||||||
| Unvaccinated current and prior season (REF) | 449 | 101 | ( | 22 | ) | REF | 471 | 253 | ( | 54 | ) | REF | 737 | 171 | ( | 23 | ) | REF | 365 | 147 | ( | 40 | ) | REF | |||||
| Primed only (with no current season dose) | 184 | 27 | ( | 15 | ) | 40 |
(1– 64) |
183 | 79 | ( | 43 | ) | 36 |
(6– 56) |
314 | 53 | ( | 17 | ) | 39 |
(11– 58) |
151 | 47 | ( | 31 | ) | 38 |
(2– 61) |
|
| Current season dose(s) only (with no prime) | 102 | 14 | ( | 14 | ) | 30 | (−35, 64) |
95 | 25 | ( | 26 | ) | 66 |
(41– 80) |
178 | 20 | ( | 11 | ) | 58 |
(27– 75) |
84 | 14 | ( | 17 | ) | 66 |
(33– 83) |
|
| Current season and prime dose(s) | 356 | 32 | ( | 9 | ) | 61 |
(37– 76) |
299 | 98 | ( | 33 | ) | 52 |
(32– 66) |
595 | 70 | ( | 12 | ) | 53 |
(34– 66) |
254 | 53 | ( | 21 | ) | 58 |
(34– 73) |
|
| Priming: ≥1 doses of any influenza vaccine in any prior seasone | |||||||||||||||||||||||||||||
| Unvaccinated in current and prior seasons (REF) | 249 | 51 | ( | 20 | ) | REF | 228 | 111 | ( | 49 | ) | REF | 396 | 81 | ( | 20 | ) | REF | 176 | 59 | ( | 34 | ) | REF | |||||
| Primed only (with no current season dose) | 384 | 77 | ( | 20 | ) | 16 | (−30, 46) |
426 | 221 | ( | 52 | ) | 8 | (−32 35) |
655 | 143 | ( | 22 | ) | 9 | (−28, 36) |
340 | 135 | ( | 40 | ) | −1 | (−57, 35) |
|
| Current season dose only (with no prime) | 46 | 7 | ( | 15 | ) | −12 | (− 187, 56) |
27 | 10 | ( | 37 | ) | 25 | (−81, 69) |
64 | 8 | ( | 13 | ) | 33 | (−55, 71) |
23 | 6 | ( | 26 | ) | 6 | (−179, 68) |
|
| Current season and prime doses | 412 | 39 | ( | 9 | ) | 58 |
(30– 74) |
367 | 113 | ( | 31 | ) | 54 |
(32– 69) |
709 | 82 | ( | 12 | ) | 51 |
(29– 66) |
315 | 61 | ( | 19 | ) | 55 |
(37, 73) |
|
| Priming: ≥2 doses of any influenza vaccine received across prior seasonsf | |||||||||||||||||||||||||||||
| Unvaccinated current season and unprimed (REF) | 378 | 78 | ( | 21 | ) | REF | 340 | 165 | ( | 49 | ) | REF | 343 | 75 | ( | 22 | ) | REF | 166 | 59 | ( | 36 | ) | REF | |||||
| Primed only (with no current season dose) | 255 | 50 | ( | 20 | ) | 26.2 | (−14, 52) |
312 | 165 | ( | 53 | ) | −10 | (−42, 26) |
708 | 149 | ( | 21 | ) | 16 | (−19, 41) |
350 | 135 | ( | 39 | ) | 10 | (−40, 42) |
|
| Current season dose only (with no prime) | 162 | 20 | ( | 12 | ) | 32.7 | (−19, 62) |
72 | 23 | ( | 32 | ) | 44 |
(1– 68) |
37 | 4 | ( | 11 | ) | 42 | (−84, 82) |
17 | 5 | ( | 29 | ) | 14 | (−184, 74) |
|
| Current season and prime doses | 296 | 26 | ( | 9 | ) | 64.8 |
(42, 79) |
324 | 102 | ( | 31 | ) | 47 |
(26– 62) |
736 | 86 | ( | 12 | ) | 53 |
(32– 68) |
321 | 62 | ( | 19 | ) | 59 |
(32– 75) |
|
| Priming: 2 doses received in the same prior seasong | |||||||||||||||||||||||||||||
| Unvaccinated current season and unprimed (REF) | 511 | 106 | ( | 21 | ) | REF | 508 | 248 | ( | 49 | ) | REF | 844 | 179 | ( | 21 | ) | REF | 398 | 138 | ( | 35 | ) | REF | |||||
| Primed only (with no current season dose) | 122 | 22 | ( | 18 | ) | 16 | (−46, 51) |
146 | 84 | ( | 58 | ) | −53 | (− 132, −1) |
207 | 45 | ( | 22 | ) | −23 | (−85, 19) |
118 | 56 | ( | 47 | ) | −56 | (− 153, 4) |
|
| Current season dose only (with no prime) | 318 | 41 | ( | 13 | ) | 37 |
(3– 59) |
254 | 95 | ( | 37 | ) | 37 |
(11– 55) |
511 | 75 | ( | 15 | ) | 33 |
(7– 52) |
h | 210 | 51 | ( | 24 | ) | 42 |
(11– 63) |
| Current season and prime doses | 140 | 5 | ( | 4 | ) | 80 |
(49– 93) |
140 | 28 | ( | 20 | ) | 58 |
(32– 75) |
262 | 15 | ( | 6 | ) | 70 | (47–83) | 128 | 16 | ( | 13 | ) | 68 |
(21– 77) |
|
Note: Non-zero VE estimates (with 95% confidence intervals [CI] that do not overlap with zero) are bolded.
Totals exclude children with illnesses associated with influenza B viruses, A(H1N1)pdm09 virus, or unsubtyped A viruses. For season 2012–13, there were 3 influenza A(H3N2) and B coinfections that were excluded. Thus, the percentage influenza positive (Flu+) is simply the number of A(H3N2) illnesses divided by the sum of influenza negatives and A(H3N2) positives. This is presented as an illustration to aid interpreting VE.
Totals exclude children with illnesses associated with influenza A viruses. Thus, the percentage of children who are influenza B virus positive (Flu B+) is simply the number of influenz B virus illnesses divided by the sum of influenza negatives and influenza B positives. This is presented as an illustration to aid interpreting VE.
Models adjusted for study site, month of enrollment, age (in months), high risk status, race/ethnicity, and days from illness onset to enrollment. The model for A(H3N2) illness also included a variable for season and an interaction term for season by month.
For season 2011–12, prior season is 2010–11; for season 2012–13, prior season is 2011–12; the prior vaccine could be inactivated or live attenuated. Receipt of monovalent A(H1N1)pdm09 vaccine was not included. Unvaccinated children received no vaccine in current nor prior season.
Any prior season includes any seasonal vaccination received prior to the current study season (either 2011–12 or 2012–13). Unvaccinated children received no current season IIV3 and have no record of any prior influenza vaccination.
Primed children had records confirmed receipt of 2 or more doses summed across prior seasons; "unvaccinated and unprimed" children did not receive current season IIV3 and did not receive 2 or more previous doses (but may have had 1 dose in one or more seasons).
Primed children received 2 doses in a single season prior to the study season; "unvaccinated and unprimed" children did not receive current season IIV3 and did not have 2 doses of any influenza vaccine in a single prior season (but may have had 2 or more doses across multiple prior seasons).
The odds of being A(H3N2) positive were 2.4-fold (95% CI = 1.4–4.3) higher among children who received IIV3 but were unprimed compared to children who received IIV3 after receiving 2 doses in a previous season.