title: The Possible Impact of Vaccination for Seasonal Influenza on Emergence of Pandemic Influenza via Reassortment.
abstract: One pathway through which pandemic influenza strains might emerge is reassortment from coinfection of different influenza A viruses. Seasonal influenza vaccines are designed to target the circulating strains, which intuitively decreases the prevalence of coinfection and the chance of pandemic emergence due to reassortment. However, individual-based analyses on 2009 pandemic influenza show that the previous seasonal vaccination may increase the risk of pandemic A(H1N1) pdm09 infection. In view of pandemic influenza preparedness, it is essential to understand the overall effect of seasonal vaccination on pandemic emergence via reassortment.
  
  
  
  In a previous study we applied a population dynamics approach to investigate the effect of infection-induced cross-immunity on reducing such a pandemic risk. Here the model was extended by incorporating vaccination for seasonal influenza to assess its potential role on the pandemic emergence via reassortment and its effect in protecting humans if a pandemic does emerge. The vaccination is assumed to protect against the target strains but only partially against other strains. We find that a universal seasonal vaccine that provides full-spectrum cross-immunity substantially reduces the opportunity of pandemic emergence. However, our results show that such effectiveness depends on the strength of infection-induced cross-immunity against any novel reassortant strain. If it is weak, the vaccine that induces cross-immunity strongly against non-target resident strains but weakly against novel reassortant strains, can further depress the pandemic emergence; if it is very strong, the same kind of vaccine increases the probability of pandemic emergence.
  
  
  
  Two types of vaccines are available: inactivated and live attenuated, only live attenuated vaccines can induce heterosubtypic immunity. Current vaccines are effective in controlling circulating strains; they cannot always help restrain pandemic emergence because of the uncertainty of the oncoming reassortant strains, however. This urges the development of universal vaccines for prevention of pandemic influenza.
authors.affiliation: Modelling and Economics Unit, Centre for Infectious Disease Surveillance and Control, Public Health England, London, United Kingdom; Medical Research Council Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College School of Public Health, London, United Kingdom.
authors.forename: Xu-Sheng
authors.initials: XS
authors.lastname: Zhang
authors.affiliation: Respiratory Diseases Department, Centre for Infectious Disease Surveillance and Control, Public Health England, London, United Kingdom.
authors.forename: Richard
authors.initials: R
authors.lastname: Pebody
authors.affiliation: Statistics Unit, Centre for Infectious Disease Surveillance and Control, Public Health England, London, United Kingdom; Medical Research Council Biostatistics Unit, University Forvie Site, Cambridge, United Kingdom.
authors.forename: Daniela
authors.initials: D
authors.lastname: De Angelis
authors.affiliation: Modelling and Economics Unit, Centre for Infectious Disease Surveillance and Control, Public Health England, London, United Kingdom; Medical Research Council Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College School of Public Health, London, United Kingdom; NIHR Health Protection Research Unit in Modelling Methodology, Department of Infectious Disease Epidemiology, Imperial College School of Public Health, London, United Kingdom.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: White
authors.affiliation: Statistics Unit, Centre for Infectious Disease Surveillance and Control, Public Health England, London, United Kingdom.
authors.forename: Andre
authors.initials: A
authors.lastname: Charlett
authors.affiliation: Medical Research Council National Institute for Medical Research, Mill Hill, London, United Kingdom.
authors.forename: John W
authors.initials: JW
authors.lastname: McCauley
mesh_terms: D003429:Cross Reactions / Q000276:immunology; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics* / Q000276:immunology; D007252:Influenza Vaccines / Q000627:therapeutic use*; D007251:Influenza, Human / Q000453:epidemiology / Q000276:immunology / Q000517:prevention & control*; D008962:Models, Theoretical; D058873:Pandemics / Q000517:prevention & control / Q000706:statistics & numerical data; D011159:Population Surveillance; D016865:Reassortant Viruses / Q000235:genetics* / Q000276:immunology; D012621:Seasons
chemical_list: D007252:Influenza Vaccines