Phylogenetic and antigenic analysis of influenza A(H3N2) viruses isolated from conscripts receiving influenza vaccine prior to the epidemic season of 1998/9.
Roughly half (54%) of the 910 young conscripts at a garrison in Finland were vaccinated with commercial influenza vaccines in autumn 1998. During the influenza outbreak in February 1999, 12 H3N2-subtype virus strains were isolated from vaccinated patients, and 11 such strains were isolated from unvaccinated patients. The isolates were related to the vaccine strain A/Sydney/5/97 and could be classified into three subgroups based on sequence variation in the HA1 gene coding for the variable domain of viral haemagglutinin (HA). A total of 6-10 amino-acid substitutions in HA1, three of these in the receptor-binding site, differentiated the field strains from the vaccine virus. In haemagglutination inhibition (HI) tests, eight strains from the study population exhibited reduced reactivity with a variety of antisera including human post-vaccination sera. Six of these strains were isolated from vaccinated and two from unvaccinated patients. The reduced reactivity did not correlate with particular amino-acid changes in HA1. We suggest that low-reactivity viruses may have an advantage over other co-circulating variants under some circumstances characterized by enhanced immunity-mediated selection and high infection pressure. Whether the frequency of these viruses increased in our vaccinated study population cannot be determined, nor can their effect on vaccine efficacy.
Pyhälä
R
R
National Influenza Centre, National Public Health Institute, Helsinki, Finland.
Ikonen
N
N
Haanpää
M
M
Santanen
R
R
Tervahauta
R
R
D000328:Adult; D000595:Amino Acid Sequence; D016022:Case-Control Studies; D004196:Disease Outbreaks; D005387:Finland; D006385:Hemagglutination Inhibition Tests; D006389:Hemagglutinins, Viral / Q000235:genetics; D006801:Humans; D053122:Influenza A Virus, H3N2 Subtype; D009980:Influenza A virus / Q000145:classification / Q000235:genetics* / Q000276:immunology*; D007252:Influenza Vaccines; D007251:Influenza, Human / Q000097:blood / Q000453:epidemiology / Q000517:prevention & control*; D008297:Male; D008889:Military Personnel; D008969:Molecular Sequence Data; D010802:Phylogeny; D012621:Seasons
D006389:Hemagglutinins, Viral; D007252:Influenza Vaccines