Table 4. Association of 2011–2012 influenza vaccine A strain seroprotection (HI titer ≥ 1:40) and seroconversion with count* of historical strains that have seroprotective titers (HI titer ≥ 1:40) at Day 0 from logistic regression: adjusted results.
| Row | Variable | 2011–2012 Influenza A Vaccine Strains | |
|---|---|---|---|
| A(H1N1) Odds Ratio (95% CI) |
A(H3N2) Odds Ratio (95% CI) |
||
| Outcome: Pre-vaccination Day 0 Titers ≥ 1:40 vs. < 1:40 | |||
| 1 | Count of seroprotective responses to historical strains | 1.43 (1.17–1.75) | 2.66 (1.95–3.64) |
| Outcome: Post-vaccination Day 21 Seroprotective Titers ≥ 1:40 vs. < 1:40: Full Data Set | |||
| 2 | Day 0 2011–2012 strain titers ≥ 40 (ref. < 40) Day 0 | 8.46 (3.94–18.15) | 6.28 (2.60–15.19) |
| 3 | Count of seroprotective responses to historical strains | 1.28 (1.02–1.61) | 1.34 (1.09–1.65) |
| Outcome: Post-vaccination Day 21 Seroprotective Titers ≥ 1:40 vs. < 1:40: Restricted to Day 0 Vaccine Seronegatives | |||
| 4 | Count of seroprotective responses to historical strains | 1.41 (1.09–1.82) | 1.32 (1.07–1.62) |
| Outcome: Seroconversion - 4-fold Rise in Day 21 Titers | |||
| 5 | Count of seroprotective responses to historical strains | 1.20 (0.96–1.50) | 1.24 (1.01–1.52) |
| 6 | log2 Day 0 2011–2012 strain titers | 0.53 (0.41–0.69) | 0.55 (0.42–0.72) |
All models adjusted for age group, sex, race, site (Marshfield vs. Pittsburgh), and diabetes. CI, confidence interval. *The number of historical strains for which each specimen had a titer ≥ 1:40 for that type was called the “historical count”; for example, if a given serum specimen were tested against 6 historical A(H1N1) viruses and had a titer ≥1:40 for 4 of them, the historical count was 4 for A(H1N1).