Flu Scan for Feb 17, 2014

Flu vaccine performance in Europe
;
H5N1 outbreaks in Vietnam
;
H7N9 study in pigs

Study: Last year's flu vaccine yielded 42% to 50% protection in Europe

Data from seven European countries suggests that last season's influenza vaccine yielded about 42% to 50% protection, depending on the flu type, according to a recent report in Eurosurveillance.

The researchers used a test-negative study design to examine flu vaccine effectiveness (VE) at sites in France, Germany, Ireland, Poland, Portugal, Romania, and Spain in 2012-13. Patients who had a influenza-like illness (ILI) were tested for flu and their vaccination status was determined. The authors are members of the Influenza Monitoring Vaccine Effectiveness in Europe (I-MOVE) network.

Europe saw circulation of H3N2, 2009 H1N1, and influenza B viruses last season. The authors counted the following numbers of ILI patients and cases for each strain: 2009 H1N1, 3,516 patients and 1,068 cases; H3N2, 3,340 patients and 730 cases; and type B, 4,627 ILI patients with 1,937 cases.

The team adjusted for age, sex, week of symptom onset, and presence of chronic conditions to come up with these adjusted VE estimates: 2009 H1N1, 50.4% (95% confidence interval [CI], 28.4%-65.6%); H3N2, 42.2% (95% CI, 14.9%-60.7%); and type B, 49.3% (95% CI, 32.4%-62.0%).

By age-group, the adjusted VE estimates were somewhat higher for 15- to 59-year-olds than for children 0 to 14 years old. There were too few elderly patients to yield an adjusted VE estimate for that age-group.

The estimates for H1N1 and type B came out lower than interim estimates that I-MOVE members calculated during the 2012-13 season (February 2013): H1N1, 50.4% versus 62.1%, and B, 49.3% versus 78.2%. The final and interim estimates for H3N2 were similar: 42.2% and 41.9%.

Previously I-MOVE members had reported that vaccine effectiveness in the preceding season (2011-12) waned by 3 to 4 months after vaccination. This time the researchers found no clear evidence of waning protection late in the season, but they noted that the samples were small, and there was a hint of waning protection against influenza B.
Feb 13 Eurosurveillance study
Jan 31, 2013, CIDRAP News story on late-season waning of protection
Jan 11, 2013, CIDRAP News story on US flu VE in 2012-13

 

Four recent H5N1 outbreaks kill 13,000 Vietnamese poultry

Four H5N1 avian flu outbreaks in separate provinces in Vietnam last week affected almost 13,000 poultry, according to a recent World Organization for Animal Health (OIE) report.

The outbreaks, in Lao Cai province in the north and Long An, Phu Yen, and Dak Lak provinces in the south, were in flocks that ranged from 1,630 to 6,813 birds. From 206 to 1,100 birds in each flock were killed by the virus, with all surviving birds in the flocks culled to prevent disease spread.

All told, the outbreaks involved 9,387 H5N1 cases, 2,771 deaths, and the culling of 10,173 poultry, for a total of 12,946 birds killed. The outbreaks began from Feb 10 to Feb 14, and disinfection of the premises is under way, according to the report.
Feb 15 OIE report

 

Avian H7N9 strains replicate better in pigs than do human strains

In a study in pigs, avian-origin H7N9 influenza viruses were found to replicate well,but human H7N9 viruses replicated poorly after three passages, Chinese researchers reported in Virology.

The team also found that nine specific mutations enhance the binding affinity for human-type receptors of avian-isolated H7N9.

The researchers found that, after they inoculated 4-week-old pigs with either the avian strain or human strain and analyzed nasal and throat swabs and lung tissue, the avian virus was able to replicate to a high titer after one passage. The human isolates, in contrast, replicated poorly even after three passages in pig lungs. None of the inoculated pigs showed any clinical signs of flu.

In addition, sequence analysis found nine substitutions in the avian isolates that led to enhanced binding affinity for human-type receptors. Except for one—Met67Ile in the hemagglutinin protein—the mutations were found in a number of H7N9 viruses in GenBank, with most in human isolates.

The authors conclude, "These results indicate that avian H7N9 influenza viruses can be easily adapted to pigs and that pigs may act as an important intermediate host for the reassortment and transmission of such novel viruses."
March Virology abstract

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