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Phylogenetic and Antigenic Analysis of Influenza A(H3N2) Viruses Isolated from Conscripts Receiving Influenza Vaccine Prior to the Epidemic Season of 1998/9
R. Pyhälä, N. Ikonen, M. Haanpää, R. Santanen and R. Tervahauta
Epidemiology and Infection
Vol. 129, No. 2 (Oct., 2002), pp. 347-353
Published by: Cambridge University Press
Stable URL: http://www.jstor.org/stable/3864963
Page Count: 7
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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.
Epidemiology and Infection © 2002 Cambridge University Press