Flu Scan for Dec 11, 2014

Flu vaccine impact in 2013-14
Avian flu in British Columbia
H7N9 severity

CDC estimates flu vaccine prevented 7 million illnesses last season

Despite the incomplete uptake and moderate effectiveness of the seasonal influenza vaccine, the Centers for Disease Control and Prevention (CDC) estimates that vaccination prevented more than 7 million illnesses and about 90,000 hospitalizations during the 2013-14 flu season.

Using updated estimates of vaccine effectiveness (VE), vaccination coverage, and flu-related hospitalizations, the agency estimated that vaccination prevented about 7.2 million (95% confidence interval [CI], 5.1 million to 9.9 million) illnesses, 3.1 million (95% CI, 2.1 million to 4.4 million) medically attended illnesses, and 90,068 (95% CI, 51,231 to 144,751) hospital stays, according to an article today in Morbidity and Mortality Weekly Report (MMWR).

If vaccination coverage had reached 70%, the Healthy People 2020 target, another 5.9 million illnesses, 2.3 million medically attended illnesses, and 42,000 hospitalizations might have been averted, the CDC said.

Overall, illnesses and hospitalizations due to flu were estimated to be 16.9% lower than they would have been without a vaccine, according to the report. This percentage was similar to estimates for previous seasons and was highest for children less than 5 years old (25%) and lowest for adults aged 20 through 64 years (15%), the CDC said.

The latter group—working-age adults—had the lowest flu vaccine coverage of any age-group, at 37%, the CDC said. In 2013-14 the group, which makes up about 60% of the population, accounted for 77% of estimated flu cases and 46% of hospitalizations, the last figure much higher than usual.

The article says flu VE last season ranged from 39% (CI, -6% to 65%) for elderly people to 56% (CI, 37% to 69%) for those aged 5 to 19; it does not list an overall VE estimate.

The CDC acknowledges several limitations of its estimation method, including that vaccine coverage estimates were based on self-reporting by survey respondents rather than vaccination records. The report notes that more-effective flu vaccines are needed, but adds that efforts to increase vaccine uptake this season will further reduce the burden of flu, especially among non-elderly adults.
Dec 12 MMWR article
Dec 12, 2013, CIDRAP News story covering CDC estimates of flu vaccine impact in 2012-13


New avian flu outbreaks bring number of affected BC farms to 8

The Canadian Food Inspection Agency (CFIA) yesterday confirmed three new avian flu outbreaks in poultry in British Columbia's Fraser Valley, bringing to eight the number of affected farms at seven separate locations.

One of the new outbreaks is at a barn adjacent to a previously affected barn (premises #5), but the two barns have different owners, so officials are counting them as separate farms, authorities said yesterday at a press briefing. They did not specify the strain, but it is presumed to be H5N2, the strain affecting the other five farms.

"This identification of additional farms is not unexpected, given that avian influenza is highly contagious," said Harpreet Kochhar, DVM, PhD, Canada's chief veterinary officer.

The new outbreaks, all near Abbotsford and within 2 miles of the first turkey farm affected in that area, bring the total number of affected birds to 155,000, said Jane Pritchard, DVM, chief veterinary officer with British Columbia's Ministry of Agriculture. The barn next to the one previously affected has about 33,000 poultry, and the other two farms house 3,750 and 5,100 broiler/breeder chickens, respectively, Pritchard said.

Culling of poultry has been completed at the first four sites and is ongoing at premises 5, the officials said. Birds at the other farms will be culled in the coming days.

Kochhar noted that countries now imposing restrictions on poultry from all of Canada, British Columbia, or the Fraser Valley include Hong Kong, Japan, Mexico, Singapore, South Africa, South Korea, and the United States.
British Columbia page with audio of Dec 10 press conference


Study: H7N9 cases more severe in second epidemic wave

While the risk of death among symptomatic human cases of H7N9 avian flu remained relatively consistent across the two epidemic waves in 2013 and 2014, the risk of death among hospitalized patients was slightly higher but the age-specific risk significantly higher in the second wave than in the latter part of the first, say results of a study from China published today in Eurosurveillance.

The first epidemic wave of human H7N9, comprising 134 case-patients of whom 124 were hospitalized, spanned January through September 2013; the second wave lasted from October 2013 to October 2014 and comprised 306 confirmed cases with 273 hospitalizations.

The authors used data reported to the Chinese Center for Disease Control and Prevention to determine hospitalization fatality risk (HFR) in confirmed H7N9 cases as well as data from the country's sentinel influenza-like illness surveillance system in urban areas to determine asymptomatic case fatality risk (CFR) in the second wave and compare them with those of the first wave.

HFR in the first wave, reported earlier, was estimated at 36% and CFR was 0.16% to 2.8%, according to the authors. In the second wave, the authors estimated HFR at 36% (95% confidence interval [CI], 28%-45%) in patients younger than 60 years of age but at 59% (95% CI, 51%-67%) in those 60 or older. CFR in the second wave was 0.10 (95% CI, 0.029%-3.6%).

The authors state that the increased risk of death in the second wave could be attributable to changes in the virus, seasonal changes in host susceptibility, or variation in treatment practices, but they note that the increase could be artifactual, caused by changes in ascertainment of cases.

They say their results "highlight that many influenza A(H7N9) virus infections can cause mild disease" and that "risk of death among laboratory-confirmed cases is a misleading measure of severity," and they conclude, "Comprehensive surveillance of avian influenza virus infections in animals and humans is essential in order to monitor risk and guide the use of control measures."
Dec 11 Eurosurveillance study

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