. 2014 Dec 17;211(12):1915–1924. doi: 10.1093/infdis/jiu622

Table 4.

Comparisons of the Duration of Immunity, Based on Day 30 and Day 180 Hemagglutination Inhibition (HI) Titers, for Recipients of High-Dose and Standard-Dose Inactivated Influenza Vaccines, by Influenza Season and Vaccine Strain

Season, Strain	Log₂ HI Titer, Day 30 − Day 180, Mean ± SD
Season, Strain	Standard Dose	High Dose
2011–2012
A/California/07/2009(H1N1)	0.3 ± 1.0	0.1 ± 1.2
A/Victoria/210/2009(H3N2)	0.0 ± 0.8	0.1 ± 1.0
B/Brisbane/60/2008	0.7 ± 0.8^a	0.7 ± 1.0^a
2012–2013
A/California/07/2009(H1N1)	0.6 ± 0.9^a	0.8 ± 1.2^a
A/Victoria/361/2011(H3N2)	−0.8 ± 2.2^a,b	−0.5 ± 2.2
B/Texas/6/2011	0.2 ± 1.5	0.5 ± 1.4^c

Abbreviation: SD, standard deviation.

^a P < .01, by the paired t test.

^b Pittsburgh experienced an outbreak of influenza A(H3N2) infection in 2012–2013, which is a possible explanation for day 180 titers exceeding day 30 titers.

^c P < .05, by the paired t test.