Increased anti-influenza A virus cytotoxic T cell activity following vaccination of the chronically ill elderly with live attenuated or inactivated influenza virus vaccine.

The possible enhancement of anti-influenza A virus memory cytotoxic T cell (CTL) responses to inactivated influenza virus vaccine by coadministration of intranasal live attenuated influenza A virus vaccine was investigated. Fifty elderly nursing home residents received inactivated trivalent influenza virus vaccine intramuscularly and simultaneously were randomly assigned to receive either bivalent live attenuated influenza A virus vaccine or saline placebo intranasally in a blinded fashion. A larger proportion of volunteers who received live attenuated virus vaccine than of those who received placebo experienced a postvaccination rise in anti-influenza A virus CTL activity (15 of 23 vs. 8 of 24; P < .05). Anti-influenza A virus cytotoxicity was primarily mediated by CD8+ T cells and was influenza A virus-specific and HLA-restricted. There was a possible advantage of administering live attenuated with inactivated virus vaccine because of enhanced memory anti-influenza A virus CTL activity.