Flu Scan for Oct 25, 2013

Recent US flu vaccine uptake
H5N1 mutation transmission
More H7N2 in Australia

CDC: Flu vaccine uptake increased in recent years

The US Centers for Disease Control and Prevention (CDC) today published a broad look at flu vaccine coverage patterns over five recent seasons—based on an analysis of eight different surveillance tools—that showed significant gains in both kids and adults. Coverage levels for all age and risk groups, however, are well below the Healthy People (HP) 2020 goal of 70% for children and adults and 90% for healthcare providers.

According to the report, the tools the CDC uses to gauge flu vaccine uptake range from the National Health Interview Survey (NHIS), which is designed to track progress on HP 2020 goals, to Internet panel surveys. The analysis, in Morbidity and Mortality Weekly Report (MMWR), includes data from the 2007-08 to 2011-12 seasons.

For children, coverage rose significantly over the five seasons, from 31.1% in 2007-08 to 56.7% in 2011-12 as measured by NHIS

For adults, flu vaccine coverage remained low but increased slightly, from 33.0% in 2007-08 to 38.3% in 2011-12 as measured by NHIS. Among adults, seniors had the highest vaccination levels—69.4% in 2011-12 according to NHIS data.

Coverage declined by age in kids but rose by age in adults. Coverage varied by state for both adults and children.

The investigators found that uptake in health providers is increasing but, at 62% in 2011-12, is still well below targets. Likewise, vaccination in pregnant women is on the rise, but only about half receive the flu shot.

The authors say that the results point to a need for more strategies to improve flu vaccine coverage, such as expanding the use of standing orders and increasing awareness in public health officials of the strengths and limitations of various methods used to gauge uptake.
Oct 25 MMWR report


Study: Uncommon H5N1 mutations may transmit in mammals

A study assessing H5N1 avian flu mutations as the virus spreads in ferrets found that mutations that were present in as few as 5.9% of the viruses infecting one ferret could be transmitted to another, according to data published this week in Nature Communications.

US and Japanese researchers, including Yoshihiro Kawaoka, DVM, PhD, of the University of Wisconsin, used data from transmission studies already conducted by Kawaoka in 2011 on engineered H5N1 strains. Publication of that controversial work was originally halted but later allowed by US biosecurity experts.

The team used deep sequencing to identify genetic mutations that happened as the virus replicated in and transmitted between ferrets. They found that during transmission natural selection acts strongly on hemagglutinin (HA), the protein the virus uses to attach to host cells.

They found that within-host genetic diversity in HA increases during replication but is dramatically reduced upon transmission via respiratory droplets—to only one or two distinct HA segments, a small portion of the viral genome.

However, the discovery that mutations present in only 5.9% of the viruses infecting one ferret could be transmitted to another suggests that even rare mutations could be transmitted if they have an evolutionary advantage, according to a Science Daily story on the study.

"Fully avian viruses may act differently in nature," said lead author Thomas Friedrich, PhD, from the University of Wisconsin. "But the data suggest to us that it wouldn't take many viruses from a chicken to infect a person, if the right mutations were there—even if they were a tiny minority of the overall virus population."
Oct 23 Nature Comm abstract
Oct 23 Science Daily story


H7N2 strikes another farm in New South Wales

An H7N2 strain of avian flu has killed 620 chickens on a farm in New South Wales, Australia, that houses 55,000 layer hens near where an outbreak occurred last week, according to a report today from the World Organization for Animal Health (OIE).

The farm listed in today's report was under surveillance because of the previous H7N2 outbreak, which the OIE confirmed on Oct 16. It houses caged layer hens 45 to 84 weeks old. Authorities will cull the remainder of the flock and disinfect the property to prevent further disease spread, the report said.

Last week's outbreak killed 18,000 of 435,000 chickens on a separate farm, and the remaining birds were subsequently culled, the OIE said.
Oct 25 OIE report
Oct 16 CIDRAP News Scan on previous outbreak

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