FLU NEWS SCAN: Antivirals and hospitalizations, type B vaccine response in kids, H1N1 reassortants in swine, test misses B variant

Aug 19, 2011

Study: Antiviral use during pandemic prevented up to 12,600 hospitalizations
A team of researchers estimates that the use of antiviral drugs during the 2009 H1N1 pandemic prevented up to 12,600 hospitalizations in the United States. The researchers, mainly from the Centers for Disease Control and Prevention, presented their findings in a report published online yesterday by Emerging Infectious Diseases (EID). Relying on the IMS Health Xponent proprietary database of prescriptions, which includes prescriptions filled at 73% of US retail pharmacies, the researchers estimated that about 8.2 million prescriptions for neuraminidase inhibitors were filled between Apr 24, 2009, and Mar 26, 2010. They estimated how many prescriptions were written for prophylaxis and personal stockpiling and how many antiviral regimens were not completed by the patients. Relying on previous studies on the effects of antivirals on hospitalization risk in different age-groups, they estimated that the drugs prevented between 8,400 and 12,600 hospitalizations for H1N1 flu. About 60% of these were among adults aged 18 to 64, and the rest were almost equally divided between those younger and older, the team estimates. The authors say their findings indicate that antivirals were used successfully during the pandemic and that public health officials should renew their planning for antiviral use in the next pandemic.
Aug 18 Emerg Infect Dis report

In small children, influenza B vaccine responses recall original dose
Small children whose first influenza vaccination included a type B virus of the Yamagata lineage continued to generate antibodies primarily to the Yamagata virus in the following 2 years when they received vaccines targeting the other type B lineage, Victoria, according to a report by Canadian researchers in the Pediatric Infectious Disease Journal. The participants were primed (received their first flu vaccination) as infants or toddlers with two doses of the 2008-09 trivalent inactivated vaccine containing a type B Yamagata lineage antigen. In the following 2 years, subsets of the original group received the 2009-10 and 2010-11 seasonal vaccines, which contained a type B Victoria antigen. Before the children received the 2009-10 vaccine, antibody to the 2008-09 antigens had fallen to low levels. In response the 2009-10 vaccine, more than 85% of the children showed a seroprotective response (defined as a hemagglutination inhibition titer of at least 40) to the original Yamagata antigen, but fewer than 25% of them showed a seroprotective response to the Victoria lineage antigen in the vaccine. When a subset of children received the 2010-11 vaccine, they again generated antibodies primarily to the original Yamagata virus rather than the Victoria virus. The authors note that this pattern of immune response has been called "original antigenic sin" (OAS). "Although OAS has been described for influenza A in humans and animal models, we are not aware of its specific evaluation in relation to influenza B," they write, adding that their findings warrant further investigation of a possible role for OAS in influenza B infection and immunization. The study did not evaluate how much protection the vaccines conferred against influenza B.
Aug 17 Ped Infect Dis J abstract

Swine surveillance turns up nine 2009 H1N1 reassortants in US
Routine influenza surveillance in US pig herds in 2009 and 2010 while the 2009 H1N1 virus was circulating found nine reassortants, which did not appear to be more pathogenic than the 2009 H1N1 strain or endemic swine flu viruses, according to a research group headed by scientists at St. Jude Children's Research Hospital in Memphis. Their report was published online today by Emerging Infectious Diseases. Samples for the study were obtained from an active surveillance program in Iowa, Indiana, Minnesota, North Carolina, and Illinois. Of 176 viruses isolated, all but one were from pigs that had respiratory symptoms. The nine reassortant viruses came from pigs in Minnesota, Indiana, and North Carolina. All but one of the viruses had hemagglutinin and neuraminidase genes from endemic swine flu viruses and M genes from the 2009 H1N1 virus. In vitro tests showed no growth differences between endemic swine viruses and the reassortants. Tests in ferrets showed that the reassortants didn't have different disease and growth properties from the 2009 H1N1 virus. The authors wrote that though finding 2009 H1N1 reassortants in US pigs was not unexpected, they didn't predict that they would see so many. They noted that they found seven distinct genotypes among the nine reassortants. The team concluded that the reassortants aren't likely to have a great impact on the health of US pig herds and that the dynamic nature of flu viruses seen in the findings shows the importance of monitoring the virus in swine populations.
Sep Emerg Infect Dis study

Possible new influenza B variant missed by routine test
The missed diagnosis in a Singaporean child of a possible new variant of influenza B is a reminder for local laboratories using molecular techniques to be constantly vigilant to the possibility of emerging virus variants that may decrease the sensitivity of their frontline assays, say the authors of a preliminary report in yesterday's Eurosurveillance. The child was a 3-year-old boy seen in April 2011. Influenza B virus was isolated from culture and confirmed by standard immunofluorescence testing, but it was not detected by a routine polymerase chain reaction assay targeting the nucleoprotein (NP) gene, the report says. Further testing is ongoing to determine if in fact the virus is a new variant. The authors say labs should have access to parallel testing using viral isolation by culture. They also advise that labs should test any assay they have developed in-house and should adapt their primers and probes accordingly to minimize the risk of missed diagnoses. The researchers further comment that it is essential for diagnostic and research labs to continuously update and share gene sequences of possible novel local viruses to allow labs to develop assays for new variants.
Aug 18 Eurosurveillance article

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