Influenza Epidemiology and Vaccine Effectiveness among Patients with Influenza-Like Illness, Viral Watch Sentinel Sites, South Africa, 2005–2009Reportar como inadecuado




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Background

There is limited data on the epidemiology of influenza and few published estimates of influenza vaccine effectiveness VE from Africa. In April 2009, a new influenza virus strain infecting humans was identified and rapidly spread globally. We compared the characteristics of patients ill with influenza AH1N1pdm09 virus to those ill with seasonal influenza and estimated influenza vaccine effectiveness during five influenza seasons 2005–2009 in South Africa.

Methods

Epidemiological data and throat and-or nasal swabs were collected from patients with influenza-like illness ILI at sentinel sites. Samples were tested for seasonal influenza viruses using culture, haemagglutination inhibition tests and-or polymerase chain reaction PCR and for influenza AH1N1pdm09 by real-time PCR. For the vaccine effectiveness VE analysis we considered patients testing positive for influenza A and-or B as cases and those testing negative for influenza as controls. Age-adjusted VE was calculated as 1-odds ratio for influenza in vaccinated and non-vaccinated individuals.

Results

From 2005 through 2009 we identified 3,717 influenza case-patients. The median age was significantly lower among patients infected with influenza AH1N1pdm09 virus than those with seasonal influenza, 17 and 27 years respectively p<0.001. The vaccine coverage during the influenza season ranged from 3.4% in 2009 to 5.1% in 2006 and was higher in the ≥50 years range 6.9% in 2008 to 13.2% in 2006 than in the <50 years age group range 2.2% in 2007 to 3.7% in 2006. The age-adjusted VE estimates for seasonal influenza were 48.6% 4.9%, 73.2%; −14.2% −9.7%, 34.8%; 12.0% −70.4%, 55.4%; 67.4% 12.4%, 90.3% and 29.6% −21.5%, 60.1% from 2005 to 2009 respectively. For the AH1N1pdm09 season, the efficacy of seasonal vaccine was −6.4% −93.5%, 43.3%.

Conclusion

Influenza vaccine demonstrated a significant protective effect in two of the five years evaluated. Low vaccine coverage may have reduced power to estimate vaccine effectiveness.



Autor: Genevie M. Ntshoe , Johanna M. McAnerney, Stefano Tempia, Lucille Blumberg, Jocelyn Moyes, Amelia Buys, Dhamari Naidoo, Marietjie

Fuente: http://plos.srce.hr/



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