Table 2.

Probability of Protection Against Reverse-Transcription Polymerase Chain Reaction–Confirmed Influenza Illness According to Various Thresholds of Log₁₀ Hemagglutination Inhibition Titer Predicted by the Dunning Regression Model

Influenza Illness Endpoint	Probability of Protection at Stated Threshold
	1:40	1:80	1:160	1:320	1:640
RT-PCR–confirmed influenza illness: A/H1N1	49.7	62.5	73.7	82.5	88.8
RT-PCR–confirmed influenza illness: A/H3N2	54.7	67.9	78.7	86.6	91.8

Per-protocol correlate of protection. Hemagglutination inhibition titer was measured at 28 days after last vaccination.

Abbreviation: RT-PCR, reverse-transcription polymerase chain reaction.