Differing Virulence of H1n1 and H3n2 Influenza Strains

Abstract

Sequential influenza A/Texas/77 (H3N2) and A/USSR/77 (H1N1) epidemics occurred during the winter of 1977-1978 in two populations under viral surveillance for influenza. In college students who reported to the Vanderbilt student health service, roughly equivalent amounts of typical influenzal disease were documented by virus isolation and total health service visits with both strains. However, considering that the college population was fully susceptible to the first introduction of H1N1 virus in 20 years and partially immune to H3N2 viruses through repeated exposure, A/USSR appeared to be a relatively less pathogenic strain. Stronger proof of this was seen in a closely monitored group of 200 largely seronegative infants and young children less than 4 years of age enrolled in an experimental vaccine clinic. In this young population, A/USSR caused no recognizable illness and A/Texas caused typical febrile respiratory disease. Thus, two influenza strains circulating in close temporal association differed in virulence when observed in carefully monitored susceptible populations.

Severity of Fever in Influenza: Differential Pyrogenicity in Ferrets Exhibited by H1N1 and H3N2 Strains of Differing Virulence

“…This result is consistent with previous observations that although these recent H l N 1 isolates grew as well, and stimulated as high an inflammatory response, in the URT of intranasally inoculated ferrets as the virulent clones of this reassortant system, they induced much lower levels of pyrexial response (Toms et al, 1977;Matsuyama et al, 1980;Coates et al, 1985). In addition, this result is in accord with their reported less severe illness in man (Kung et al, 1978;Wright et al, 1981;Frank et al, 1985).…”

“…The recent H 1N 1 isolates produce relatively mild illness in man (Kung et al, 1978 ;Wright et al, 1981) and in a study of primary H3N2 and H1N l influenza virus infections in children between 1977 and 1982, infection with the H 1N 1 strains resulted in a smaller proportion of cases developing fever, and lower mean febrile temperatures, than infection with H3N2 strains (Frank et al, 1985). Influenza viruses also produce differing febrile responses in ferrets.…”

Common community respiratory viruses in patients with cancer

“…Influenza viruses also have the unique characteristic of antigenic variability, which permits recurrent epidemics despite widespread prior exposure of the population to influenza vaccines. 26 Two forms of antigenic variation are recognized: antigenic drift and antigenic shift.…”

Differential induction of cytotoxicity and apoptosis by influenza virus strains of differing virulence.

“…and correlates with the onset of fever (Sweet et al, 1979). The clinical effects of H3N2 influenza viruses in man are more severe than those of H1N1 viruses (Wright et al, 1980), and in ferrets a H3N2 strain (clone 7a) induced a significantly higher and longer fever than a H1N1 strain (A\Fiji) (Coates et al, 1986). Since both viruses replicated similarly in the URT and produced similar inflammatory responses, this indicated a greater fever-producing capacity of clone 7a than that of A\Fiji, an observation confirmed by direct injection of large quantities of both live and UV-inactivated viruses into ferrets Author for correspondence : Clive Sweet.…”