Study: Children, middle-aged most vulnerable to variant H3N2
Aug 10, 2012 (CIDRAP News) – A serologic study from Canada suggests that children and middle-aged adults have little or no immunity to the swine-origin variant H3N2 influenza virus (H3N2v), but about half of adolescents and young adults have some degree of immunity as measured by antibody levels.
The researchers also found that seasonal flu vaccines used in the past two seasons did not improve participants' ability to mount an immune response to H3N2v. Their report was published this week in the Journal of Infectious Diseases.Given the results, "A specific vaccine would be needed in the event A(H3N2)v establishes epidemic spread," says the study, which was led by Danuta M. Sowronski, MD, of the British Columbia Centre for Disease Control as first author.-snip-
The CDC has prepared a candidate vaccine for the novel virus, and clinical trials are expected this fall.
A CDC expert, Jacqueline Katz, PhD, said the Canadian findings generally agree with previous smaller studies conducted by her agency and a group in Norway. But she said the study is much larger and offers greater insight into the age-related differences in seroprotection against H3N2v. Katz is chief of the immunology and pathogenesis branch of the CDC's Influenza Division.
"Overall, the three studies agree that there is negligible cross-reactive antibody to the H3N2v virus detected in younger children," Katz said. The work also confirms previous findings that seasonal trivalent flu vaccine containing an H3N2 strain does not trigger much of a cross-reactive response to the novel virus, she added."What's novel about Skowronski's study is it's the largest to date and had the ability to look more closely at different age groups," she said. "They have quite an interesting finding that middle-aged adults, ages 40 to 69, show a substantial reduction in the level of cross-reactive antibody compared with younger adults."The Norwegian study had a similar finding, but in a tighter age-group of adults, she said, adding that further research is warranted to try to find an explanation for the phenomenon.Katz concurred with the Canadian team's suggestion that different childhood exposures may be a reason for the age-related differences in seroprotection."It may be that that particular group [middle-aged adults] had a different exposure, that they saw an earlier H3N2 virus for the first time, and didn't have the same robustness of response to the viruses from the 1990s that are closest to the H3N2v strain," she said. "We're interested in looking into that a little more.""When you do genetic and antigenic analysis, you can see that viruses from the early 1990s are genetically most closely related to the hemagglutinin of the H3N2 variant viruses," Katz said. "So it does make sense that individuals who were of an age to be exposed to those in the early 1990s and made a robust response may have the highest cross-reactive antibody response to the variant strain."
CDC: (I'll put this over on the right side-bar for future reference):
Influenza A (H3N2) Variant Virus Outbreaks
Since July 2012, there have been outbreaks of H3N2 variant viruses with the matrix (M) gene from the 2009 H1N1 pandemic virus in multiple U.S. states. Investigations into H3N2v cases indicate that the main risk factor for infection is prolonged exposure to pigs, mostly in fair settings. Found in U.S. pigs in 2010 and humans in July 2011, this virus appears to spread more easily from pigs to people than other variant viruses. Though limited person-to-person spread with this virus has occurred, no sustained community spread of H3N2v has been detected at this time. Associated illness so far has been mostly mild with symptoms similar to seasonal flu and most cases have occurred in children who have little immunity against this virus. Like seasonal flu, however, serious illness, resulting in hospitalization and death is possible. People at high risk of serious complications from H3N2v include children younger than 5, people with certain chronic conditions like asthma, diabetes, heart disease, weakened immune systems, pregnant women and people 65 years and older. These people are urged to avoid pigs and pig arenas at fairs this season. The Centers for Disease Control and Prevention (CDC) is working with states to respond to these outbreaks and continues to monitor the situation closely.
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