# 6278
From the CDC’s MMWR today we get a study that looked for the presence of serum cross-reactive antibodies to the recently emergent H3N2v (variant) swine flu virus among the U.S. population by age groups.
By way of background, over the past year a small number of novel H3N2v influenza infections have been detected (13 across 6 states), affecting primarily children under the age of 10.
The most recent case was reported yesterday (see Novel (H3N2v) Flu Detected In Weber County, Utah).
In an attempt to see what levels of pre-existing immunity might be present in the population, researchers looked at serum samples from two sources; a 2010–11 TIV study and the 2007–2008 National Health and Nutrition Examination Survey (NHANES).
What they were looking for was evidence of cross-reactive antibodies to the H3N2v virus by age cohorts – antibodies that might provide some degree of immunity against the H3N2v strain - and if those antibodies were boosted by the receipt of the 2010–11 seasonal trivalent influenza vaccine (TIV).
What they found was that children under the age of 10 had few or no cross-reactive antibodies to the H3N2v strain, suggesting they would be the most vulnerable age group to the virus.
Based on the small sampling of tests conducted, approximately 1/3rd of those aged 10–49 years displayed cross-reactive antibodies that might provide some protection against infection from the H3N2v virus.
Receipt of the 2010-11 TIV boosted antibody titers in some adults and teenagers (but not children < 3), but to a lesser extend that it did for seasonal H3N2.
For the details on how this study was conducted, you’ll want to read the entire release at the link below. But for the short version, you can skip to the summary after the link.
Antibodies Cross-Reactive to Influenza A (H3N2) Variant Virus and Impact of 2010–11 Seasonal Influenza Vaccine on Cross-Reactive Antibodies — United States
Weekly
April 13, 2012 / 61(14);237-241
The short version is summarized in the report as follows:
What is already known on this topic?
Twelve human infections with influenza A (H3N2)v virus were detected in the United States in 2011, compared with eight cases in the preceding 2 years. Most of these cases were in children aged <10 years.
What is added by this report?
Children aged <10 years have few or no cross-reactive antibodies to A (H3N2)v virus, but some older children and adults do have cross-reactive antibodies to the virus. Vaccination with the 2010–11 seasonal influenza vaccine had no impact on cross-reactive antibody levels in children aged <3 years but did boost cross-reactive antibodies in adults aged 18–49 years and ≥65 years, but only to levels that were lower than to seasonal A (H3N2) virus.
What are the implications for public health practice?
In the event of sustained human-to-human transmission of A (H3N2)v virus, children aged <10 years are likely to be the most susceptible to infection among groups studied.
Although unlikely to protect against A (H3N2)v in this susceptible age group, receipt of seasonal influenza vaccine continues to be recommended to protect against circulating human influenza viruses for all age groups and might provide some protection against A (H3N2)v infection in the adult population.
A vaccine virus specific for A (H3N2)v has been developed and could be used to produce an H3N2v vaccine, if needed.
Percentage titer achievement for cross-reactive hemagglutination inhibition (HI) and microneutralization (MN) antibodies to influenza A (H3N2) variant virus* before and after receipt of 2010–11 trivalent inactivated seasonal influenza vaccine, by age group — United States
