Jan 31, 2013
Studies find modest flu vaccine effectiveness in Canada, UK
Vaccine effectiveness (VE) against lab-confirmed influenza so far this flu season has been about 52% in Canada and 51% in the United Kingdom, slightly lower than recent US midseason estimates, according to separate studies in Eurosurveillance today. In the Canadian study, researchers compared data on 355 patients (cases) who tested positive for flu (17% of whom had been vaccinated) with 384 controls who tested negative, 27% of whom had received a flu vaccine. They found an adjusted VE of 52% overall (95% confidence interval [CI], 25%-69%), but only a 45% VE (95% CI, 13%-66%) against H3N2 strains, which constituted 86% of the case strains that were subtyped. In the UK study, investigators studied data on 498 patients who had lab-confirmed flu, 8% of whom had been vaccinated, and 1,203 test-negative controls, 19% of whom had been vaccinated. They found an adjusted overall VE of 51% (95% CI, 27%-68%), with a VE against influenza A of 49% (95% CI, -2% to 75%) and a VE against influenza B of 52% (95% CI, 23%-70%). Of the 498 cases of flu, 377 (76%) were caused by influenza B. Both studies involved patients and controls of all ages. A few weeks ago a US study found a 62% overall VE, a 55% influenza A VE, and a 70% influenza B VE.
Jan 31 Eurosurveill Canada report
Jan 31 Eurosurveill UK report
Jan 11 CIDRAP News story on US flu VE
Dutch study detects circulation of influenza B in seals
Influenza B continues to circulate in various types of seals, keeping alive the possibility that the animals could be a reservoir for the virus in humans, says a letter yesterday in Emerging Infectious Diseases describing work by Dutch researchers. Until 1999, influenza B was considered to be an infection of humans only. That belief was challenged by sporadic reports of the infection in pinnipeds, but whether the virus has continued to circulate has been unknown. The authors analyzed serum samples from 615 harbor and gray seals living in Dutch coastal waters from 2002 through 2012 that were admitted to the Seal Rehabilitation and Research Centre in Pieterburen. Animals were tested by hemagglutination inhibition assay, usually within 1 day of arrival at the facility. Influenza B virus–specific antibodies were not detected in samples collected from 2002 to 2009 or in 2012. In 2010, however, antibodies were identified in 9 of 21 samples, and in 2011 in 1 of 150 samples, with all but one positive sample from seals 6 to 12 months of age, when maternal antibodies would have declined to undetectable levels. This means the young seals had been infected in late 2009 through early 2010, say the authors, suggesting novel introduction of an influenza B virus by either seals or another source.
Jan 30 Emerg Infect Dis letter