Background: The aim of this study was to assess humoral response to influenza vaccine in children with acute lymphoblastic leukemia.
Methods: Studies were performed in 25 patients previously vaccinated against influenza (Group A) and in 20 children who had never been immunized before (Group B). In Autumn, 1996, they were vaccinated with subunit trivalent influenza vaccine containing 15 microg of hemagglutinin of A/Singapore/6/86, A/Wuhan/359/95 and B/Beijing(184/93. Antihemagglutinin (HI) and antineuraminidase antibody titers were determined before immunization and 3 weeks and 6 months after vaccination by the hemagglutinin inhibition test and the neuraminidase inhibition test. All results were presented as the geometric mean titer of antibodies, mean fold increase of antibody titer, protection rate and response rate.
Results: In Group A mean fold increase of HI antibodies ranged from 17.2 to 26.7 three weeks after vaccination and from 22.1 to 38.2 six months after vaccination, while in Group B it ranged from 15.7 to 22.6 and from 30.3 to 39.3, respectively. In the case of neuraminidase, mean fold increases for Group A varied from 9.2 to 13.2 three weeks after immunization and from 15.6 to 21.1 six months after vaccination, whereas for Group B they varied from 5.5 to 8.3 and from 14.4 to 23.4, respectively. Six months after vaccination the proportion of subjects with HI antibodies > or = 1:40, as well as those with at least 4-fold increase of HI antibody titers, ranged from 68 to 100% in Group A and from 90 to 100% in Group B. No vaccinated child was infected with the influenza virus; the vaccine was well-tolerated and did not cause any adverse reactions.
Conclusions: The results obtained in this study indicate that influenza vaccine is immunogenic in patients with acute lymphoblastic leukemia, despite their serious disease.