NEWS SCAN: Flu vaccine link to H1N1, low US flu activity, CDC flu vaccine effectiveness resource, H5N1 evolution, lettuce Listeria recall

Oct 14, 2011

Study: No confounders in link between seasonal vaccine and H1N1 flu
An association between seasonal flu vaccine and lab-confirmed pandemic 2009 H1N1 flu (pH1N1) could not be attributed to any potential statistical confounder, according to a study by Canadian and Dutch researchers. The team analyzed data from a case-control study of 462-lab confirmed pH1N1 cases and 484 test-negative controls. They found that case-patients were more likely to have received the seasonal flu vaccine after they adjusted for multiple confounders using multivariate regression (odds ratio [OR], 1.82; 95% confidence interval [CI], 1.25-2.65), using propensity matching (OR, 1.86; 95% CI, 1.19-2.92), and in subsequent sensitivity analyses. They calculated that, for a non-significant association, an unmeasured confounder would need a prevalence of 20% and an OR of 3.5 or more with the vaccine and 3.0 or more with pH1N1. The authors conclude that the seasonal flu vaccine's relationship with pH1N1 "was not likely explained by an unmeasured confounder."
Oct 12 Vaccine abstract

CDC: First flu report of new season shows little activity
In its first report for the US 2011-12 flu season, the Centers for Disease Control and Prevention (CDC) said today that flu activity is low, with all measures below baselines. The number of respiratory specimens testing positive for flu for the previous week was 1.2%. Flu viruses identified so far include 2009 H1N1, H3N2, and influenza B, the CDC said. No locations reported widespread, regional, or local geographic spread of flu. Sporadic activity was reported by 20 states, plus the District of Columbia, Puerto Rico, and the US Virgin Islands. Joe Breese, MD, chief of the CDC's Influenza and Epidemiology Prevention Branch, said in a press release e-mailed to reporters today that the circulating flu strains so far are a good match to the ones included in the seasonal flu vaccine. Though officials can't predict exactly when flu activity will intensify, the number of cases is likely to increase over the next few weeks, he said, adding that now is a good time to be vaccinated, because it takes about 2 weeks for a full immune response. As of late September, 110 million doses of flu vaccine had been delivered, with manufacturers expecting to produce a record 166 million to 173 million doses, the CDC said.
Oct 14 CDC influenza update

CDC backgrounder helps health providers interpret flu vaccine effectiveness
The CDC recently posted a background document to brief healthcare professionals on issues surrounding flu vaccine effectiveness. Compared with information on the topic posted earlier for consumers and healthcare providers, the latest information provides more details on how researchers assess how well flu vaccines work. The new document, dated Oct 12, describes the difference between vaccine efficacy studies—randomized controlled trials that have lab-confirmed flu as the endpoint—and vaccine effectiveness studies, which are observational studies that can sometimes be affected by bias and have endpoints that may be less specific indicators of flu. The CDC notes that although vaccine efficacy studies are the gold standard, the relatively new universal flu vaccination recommendation, which applies to most people aged 6 months and older, makes it unethical to perform them. It adds that effectiveness estimates can equal those from efficacy studies. The document details the types of bias, such as selection, that can affect interpretation of vaccine effectiveness studies and notes that lab-confirmed flu provides the most specific estimate in those studies. Estimates of effectiveness can vary widely, depending on how well the viruses in the vaccine match circulating strains, the CDC said. The review also details what is reported in the medical literature about how effective the flu vaccine is in different groups, such as people with chronic conditions, older adults, and children, and what is known about the protection provided by different types of flu vaccines. The CDC notes that it conducts annual vaccine effectiveness studies among all age-groups, with targeted studies on some specific issues, such as flu-related hospitalizations in seniors.
Oct 12 CDC flu vaccine effectiveness document

Poultry vaccination may enhance H5N1 evolution
Highly pathogenic H5N1 avian flu viruses in countries that mass-vaccinate poultry appear to evolve more rapidly than viruses in countries that do not, a study in Vaccine revealed. An international research team analyzed 751 H5N1 sequences from Egypt, Indonesia, Nigeria, Turkey, and Thailand, noting that the first two nations practice mass vaccination, while the other three do not. The team wrote, "Although the direct association between H5N1 vaccination and virus evolution is difficult to establish, we found evidence for a difference in the evolutionary dynamics of H5N1 viruses among countries where vaccination was or was not adopted." The mean rates of evolution among viruses, in thousandths of a nucleotide substitution per site per year, were: Egypt, 5.36; Indonesia, 6.13; Nigeria, 5.20; Turkey, 4.04; and Thailand, 2.52. In Egypt, the subclade most widely circulating in poultry, subclade B, had a rate of 8.87. As a measure of selection pressure, the investigators also assessed the number of positively selected sites in the hemagglutinin gene of viruses from the various countries: Egypt, 9; Indonesia, 6; Nigeria, 2; Turkey, 0; and Thailand, 3. The authors emphasize that vaccination, when properly planned and adopted, is a powerful tool against H5N1. But they conclude that, if it's not properly implemented, "vaccination may contribute to the rapid evolution and antigenic change of H5N1 viruses, creating opportunities for the viruses to escape from vaccine protection."
Oct 12 Vaccine abstract

Listeria finding prompts shredded lettuce recall
Giant Eagle, a Pittsburgh-based grocery chain, has recalled packages of Giant Eagle Farmer's Market shredded iceberg lettuce because of possible Listeria monocytogenes contamination, according to an Oct 12 recall notice from the US Food and Drug Administration (FDA). The company said it launched the recall after the FDA notified it that routine sampling had turned up the pathogen in a package of the lettuce. No illnesses have been reported. The recalled lettuce was produced by River Ranch Foods, LLC, based in Salinas, Calif. The 8-ounce packages have a use-by date of Oct 14. The lettuce was also used in a small number of Giant Eagle prepared deli sandwiches.
Oct 12 FDA recall notice
The recall is the second Listeria recall affecting packaged lettuce products in recent weeks. On Sep 29 True Leaf Farms, based in San Juan Bautista, Calif., recalled 90 cartons of chopped romaine lettuce after random testing detected Listeria in a single bag. No illnesses have been associated with that recall, either.
Sep 29 FDA recall notice

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