Flu Scan for Jul 10, 2014

UK flu vaccine effectiveness
China swine flu changes

UK study finds low H3N2 vaccine protection in 2012-13

An analysis of flu vaccine effectiveness (VE) during the 2012-13 season in the United Kingdom found moderate protection against influenza B, good protection against the 2009 H1N1 virus, but very poor protection against H3N2.

A research team from several European countries used a test-negative study design and surveillance data from five primary care sentinel sites, including swabbing results from 4,649 people. They published their findings today in Eurosurveillance.

The UK flu season was long that year, marked by early outbreaks of influenza B, followed by H3N2 activity that lasted late into the season.

The researchers found that VE against H3N2 was only 26% (95% confidence interval [CI], -4% to 48%), for 2009 H1N1 it was 73% (95% CI, 37%-89%)—although data were based on only 127 cases—and for influenza B it was 51% (95% CI, 34%-63%). Also, partly because about three fourths of influenza A cases studied involved H3N2, VE for both influenza A strains was only 35% (95% CI, 11%-53%).

In addition, the team found evidence, though not significant, that VE declined over time against H3N2.

Results pointed to a second year of low VE against H3N2, which the researchers said supported the World Health Organization (WHO) recommendation for a change to a cell-propogated H3N2 vaccine virus. They also said the lower VE against influenza B reflects antigenic drift away from that season's vaccine strain, findings that also triggered a WHO-recommended change to a different influenza B component.

The team wrote that the test-negative design has now become the most commonly used approach for evaluating flu VE, because it is simple and involves a well-matched control group. They added that late-season nursing home outbreaks also hint at waning protection, and continuous VE monitoring is needed to gauge the impact of vaccine strain changes and introductions of different vaccine schemes, such as the intranasal vaccine for younger UK children.
Jul 10 Eurosurveill report


Study finds 2009 H1N1 impact on Chinese swine flu viruses

A genetic analysis shows that repeated introduction of 2009 H1N1 influenza into Chinese swine over the past few years appears to have changed the makeup of circulating swine influenza viruses (SIVs), a development that bears watching in case the viruses jump to humans, according to a new study.

To assess the impact, the research team from China looked at the complete genomes of 387 SIVs that were collected from 2009 to 2012 as part of the country's flu surveillance, according to the study in the Journal of Virology.

The investigators found 17 reassortants that had genes from the 2009 H1N1 virus, along with evidence suggesting that internal genes from the former pandemic virus have become established and are now the predominant lineage in Chinese pigs. The main reassortants had at least five 2009 H1N1 internal genes with surface genes that were European avian-like (EA) or human H3N2-like.

The researchers said the findings point to a change in the evolution of Chinese SIVs, with the possibility that 2009 H1N1 internal genes might be replacing EA- or triple-reassortant–like internal genes.
Jul 9 J Virol abstract

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