Related Experiment Videos
Influenza A (H3N2) outbreak, Nepal.
Luke T Daum1, Michael W Shaw, Alexander I Klimov
1Air Force Institute for Operational Health, Brooks City Base, San Antonio, Texas 78235, USA. Luke.Daum@brooks.af.mil
Emerging Infectious Diseases
|August 17, 2005
Summary
Influenza A (H3N2) viruses in Nepal showed significant antigenic drift from the 2004 vaccine strain. This viral evolution necessitated a vaccine strain update for the 2005-2006 influenza season.
Area of Science:
- Virology
- Epidemiology
- Immunology
Background:
- An influenza A (H3N2) outbreak occurred in Bhutanese refugee camps in Nepal in July 2004.
- This outbreak provided an opportunity to study viral evolution and vaccine strain matching.
Purpose of the Study:
- To investigate the antigenic properties of H3N2 influenza viruses isolated during the 2004 Nepal outbreak.
- To compare these isolates with the contemporary A/Wyoming/3/03 vaccine strain.
- To inform influenza vaccine strain selection for the subsequent season.
Main Methods:
- Hemagglutination inhibition assays were used to assess antigenic distinctness.
- Amino acid sequencing of viral isolates was performed.
- Comparison of isolate sequences with the A/Wyoming/3/2003 vaccine strain.
Main Results:
- Approximately 40% of H3N2 isolates were antigenically distinct from the A/Wyoming/3/03 vaccine strain.
- Four key amino acid substitutions were identified in most isolates compared to the vaccine strain.
- Substitutions were located in or near antibody-binding sites, including a notable K145N substitution.
Conclusions:
- H3N2 influenza viruses continue to evolve, demonstrating antigenic drift from established vaccine strains.
- The observed substitutions suggest ongoing viral adaptation and potential immune escape.
- The 2005-2006 Northern Hemisphere vaccine strain was updated to A/California/7/2004 to better match circulating strains.