In a trial of influenza virus vaccines, 3,103 students (13.6% of a campus population) were given a standard dose of vaccine (400 chick-cell agglutination [CCA] units of influenza A and 300 CCA units of influenza B) in October or December 1971. Fifty-eight percent of the vaccinees received a tri-(n-butyl) phosphate (TNBP) split virus vaccine; 42% received inactivated whole virus vaccine. In January, a discrete influenza outbreak occurred. Influenza A/HK virus (H3N2) was recovered as the predominant infecting agent. In a three-week period, 168 students sought medical assistance for febrile influenza. Only eight (4.8%) of these were vaccinees, representing a 69% reduction from the attack rate in nonvaccinees. The protection derived from split virus and whole virus vaccine was similar.
Ruben FL, Akers LW, Stanley ED, Jackson GG. Protection With Split and Whole Virus Vaccines Against Influenza. Arch Intern Med. 1973;132(4):568-571. doi:10.1001/archinte.1973.03650100082015