Three split-virion vaccines (Vaxigrip, Begrivac, and Influsplit/Fluarix) and 
three subunit vaccines containing only viral surface glycoproteins (Influvac, 
Agrippal, and Fluvirin) available for the 1994-95 season were analysed by 
biological, molecular, and biochemical methods. Although all vaccines are 
required by health authorities to contain 15 micrograms haemagglutinin per dose 
of each virus strain, there were significant differences in haemagglutination 
titres among the examined vaccines of both types. The enzymatic activity of 
neuraminidase was present in all vaccines except Fluvirin. Total protein content 
was lower for subunit vaccines. Viral nucleoprotein was detected in all split 
vaccines but to varying levels according to SDS-PAGE and Western blot analyses. 
The ovalbumin content was low in general but was about tenfold higher for 
Influvac than for the other vaccines analysed. This protein may induce 
hypersensitive reactions among persons with severe egg allergy. All three 
split-virion vaccines were found to contain the matrix protein; however, it was 
not detected in the subunit vaccines. Differences in influenza antigen variety 
in currently available vaccines may affect efficacy, whereas differences in 
concentrations of nonviral compounds such as ovalbumin and endotoxin may lead to 
different postvaccination reactogenicity profiles.