Posted on the Pediatric SuperSite on November 25, 2009
Seasonal vaccine may not induce cross-reactive antibody response to
influenza A (H1N1)
Cross-reactive antibody response by a factor of four may
have occurred in fewer than 20% of adults who were vaccinated with recent
seasonal influenza vaccines, according to results of a recent study.
The results indicated that individuals aged younger than
30 years demonstrated little evidence of cross-reactive antibodies to the
current strain, but that a proportion of older adults may have pre-existing
cross-reactive antibodies.
The researchers used a microneutralization assay to
measure cross-reactive antibodies to influenza A (H1N1) in stored serum
samples. The samples had been taken from individuals who had donated blood or
were vaccinated with the recent seasonal vaccine or the 1976 swine influenza
vaccine.
Among 107 individuals born after 1980, 4% had
pre-existing cross-reactive antibody titers of 40 or more against the current
pandemic strain. Among 115 individuals born before 1950, 34% had titers of 80
or more.
Among individuals vaccinated with seasonal trivalent
inactivated influenza vaccines, an increase in the level of cross-reactive
antibody to influenza A (H1N1) by a factor of four or more was observed in 0%
of 55 children aged six months to nine years old, 12% to 22% of 231 of adults
aged 18 to 64 years and in 5% or less of 113 adults older than 60.
There was no association between vaccines that were
formulated with adjuvant and enhanced cross-reactive antibody response.
Substantially boosted cross-reactive antibodies to
influenza A (H1N1) were observed in adults who had received the A/New
Jersey/1976 swine influenza vaccine.
Hancock K et al. N Engl J Med.
2009;361:1945-1952.
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