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Update: influenza activity--worldwide, March-August 1997
Abstract:
During the October 1996-March 1997 influenza epidemic season, influenza activity was moderate to severe in the Northern Hemisphere. In Europe, Japan, and North America, influenza A(H3N2) viruses predominated, but influenza B viruses were more commonly isolated by the end of the season. In contrast, in some countries in the World Health Organization (WHO) region of Asia (e.g., China, Iran, and Israel), influenza B viruses were isolated more frequently than influenza A(H3N2) viruses. Influenza A(H1N1) viruses were isolated infrequently worldwide, except in Europe, where 14 countries reported sporadic isolations, and a late-season outbreak in April affected children in the Czech Republic. Since March 1997, influenza activity has increased in the Southern Hemisphere, and outbreaks and epidemic level activity have been associated with both influenza A(H3N2) and influenza B viruses. This report summarizes worldwide influenza activity during March-August 1997, as reported through WHO, the WHO international network of collaborating laboratories, and U.S. state and local health departments, and characterizes influenza isolates collected during March-July.
Insights
Influenza A(H3N2) and B viruses predominated globally during the 1996-1997 season, with regional variations. Influenza activity increased in the Southern Hemisphere by March 1997.
Area of Science:
- Virology
- Epidemiology
- Public Health
Background:
- The 1996-1997 influenza season exhibited moderate to severe activity in the Northern Hemisphere.
- Influenza A(H3N2) viruses were initially dominant, with a later increase in influenza B virus circulation.
- Regional variations in predominant influenza strains were observed, particularly in Asia.
Purpose of the Study:
- To summarize global influenza activity from March to August 1997.
- To characterize influenza virus isolates collected between March and July 1997.
- To provide an overview of influenza epidemiology and virology during the specified period.
Main Methods:
- Data collection through the World Health Organization (WHO) and its international network of collaborating laboratories.
- Inclusion of reports from U.S. state and local health departments.
- Characterization of influenza virus isolates.
Main Results:
- Influenza A(H3N2) and B viruses were the primary circulating strains globally.
- Influenza B viruses became more common later in the season in Europe, Japan, and North America.
- Influenza B viruses predominated over influenza A(H3N2) in some Asian countries.
- Influenza A(H1N1) was infrequent globally, with notable exceptions in Europe and the Czech Republic.
- Increased influenza activity, including outbreaks, was noted in the Southern Hemisphere from March 1997 onwards, linked to both A(H3N2) and B viruses.
Conclusions:
- The 1996-1997 influenza season was characterized by the predominance of influenza A(H3N2) and B viruses, with distinct geographical patterns.
- Shifts in viral prevalence occurred within the season, highlighting the dynamic nature of influenza epidemiology.
- The findings underscore the importance of global surveillance for monitoring influenza activity and informing public health strategies.