title: Influenza epidemiology and vaccine effectiveness among patients with influenza-like illness, viral watch sentinel sites, South Africa, 2005-2009.
abstract: 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 A(H1N1)pdm09 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 A(H1N1)pdm09 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 A(H1N1)pdm09 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 A(H1N1)pdm09 season, the efficacy of seasonal vaccine was -6.4% (-93.5%, 43.3%).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Division of Public Health Surveillance and Response, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Genevie M
authors.initials: GM
authors.lastname: Ntshoe
authors.affiliation: Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Johanna M
authors.initials: JM
authors.lastname: McAnerney
authors.affiliation: Influenza Division, United States Centers for Disease Control and Prevention, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Stefano
authors.initials: S
authors.lastname: Tempia
authors.affiliation: Division of Public Health Surveillance and Response, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Lucille
authors.initials: L
authors.lastname: Blumberg
authors.affiliation: Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Moyes
authors.affiliation: Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Amelia
authors.initials: A
authors.lastname: Buys
authors.affiliation: World Health Organisation, Geneva, Switzerland.
authors.forename: Dhamari
authors.initials: D
authors.lastname: Naidoo
authors.affiliation: Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Marietjie
authors.initials: M
authors.lastname: Venter
authors.affiliation: World Health Organisation, Geneva, Switzerland.
authors.forename: Terry
authors.initials: T
authors.lastname: Besselaar
authors.affiliation: Centre for Vaccines and Immunology, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Barry D
authors.initials: BD
authors.lastname: Schoub
authors.affiliation: School of Health Systems and Public Health, University of Pretoria, Pretoria, South Africa.
authors.forename: Bernice N
authors.initials: BN
authors.lastname: Harris
authors.affiliation: Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases of the National Health Laboratory Service, Johannesburg, South Africa.
authors.forename: Cheryl
authors.initials: C
authors.lastname: Cohen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology / Q000302:isolation & purification / Q000502:physiology; D007252:Influenza Vaccines; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control*; D008875:Middle Aged; D058873:Pandemics / Q000517:prevention & control; D012621:Seasons; D018571:Sentinel Surveillance; D013019:South Africa / Q000453:epidemiology; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines
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