[Influenza season 1998/99; composition of vaccine for 1999/2000]

The first indication of influenza activity in the Netherlands in the 1998/'99 season was the isolation of an influenza B virus in week 47 of 1998. In subsequent weeks influenza activity slowly increased, reaching a peak in week 6 of 1999. After a gradual decline for three weeks a second peak was reached in week 8 of 1999. The first wave of influenza activity was primarily caused by influenza B viruses, whereas during the second wave predominantly influenza A viruses of the A/H3N2 subtype were isolated. The antigenic properties of the influenza A viruses resembled those of the viruses isolated in the previous season and the vaccine strain A/Sydney/5/97. The influenza B viruses did not completely match with B/Harbin/7/94 which is most commonly used for vaccine production. The vaccine, however, did provide good protection against the epidemic strains of influenza. This season influenza A/H1N1 viruses did not play a significant part and only a small number of viruses of this subtype were isolated at the end of the season. For the influenza season 1999/2000 it is recommended by the World Health Organization that the vaccines contain the following (or similar) virus strains: A/Sydney/5/97 (H3N2), A/Beijing/262/95 (H1N1) and B/Beijing/184/93.