Influenza - World Weekly Summary

Influenza viruses circulate around the world at different times of the year. Some of these viruses can cause serious illness in persons with pre-disposing chronic illnesses. The 2009 pandemic H1N1 strain (swine flu) is still circulating in many countries and can cause serious illness and death in many age groups, especially in younger persons.

The number of persons consulting health-care providers for influenza-like illness may increase above normal levels. Although not all influenza-like illness is actually due to influenza viruses, the number of people who seek medical care for this illness is a good measure of the level of circulation of influenza viruses.

North America - USA

Influenza viruses are now circulating in all 50 states and are widespread in 37. There is a high level of virus circulation in 20 states, a moderate level in 9 states, and a low level reported in all other states, including New York City. Since October 1, 2010, 54% of the laboratory identified influenza viruses have been the seasonal flu strain (H3N2), while 13% have been the 2009 pandemic H1N1 strain (swine flu). Type B influenza has accounted for 33% of the identified viruses.

North America - Canada

While flu activity has started to decline in most provinces, there has been increased circulation of flu viruses in Quebec and the Atlantic provinces. Since the beginning of the flu season, 87.0% of the laboratory tests were the seasonal virus (H3N2). Influenza B virus continues to increase as a proportion of positive flu cases.

Europe -

Overall, flu transmission continues to be high and is increasing in some European countries, while the countries in north Europe are beginning to record decreasing trends. The dominant flu virus in Europe is still the 2009 pandemic strain, H1N1 (swine flu). The seasonal flu strain (H3N2) has accounted for only 6% of the identified cases.

In the western European countries, hospital admissions due to flu are declining while the eastern countries report an increase. In France, persons admitted to the hospital for intensive care are found to be infected with the 2009 pandemic H1N1 strain (90%)

North Africa and the Middle East -

Flu transmission in North Africa and the Middle East appears to have peaked, although a few countries, e.g., Algeria, are reporting increasing activity. The 2009 pandemic H1N1 strain (swine flu) and type B viruses are co-circulating in nearly equal numbers.

Northern Asia -

The flu-like illness activity has been variable in different countries in northern Asia. Several countries have noted a peak of flu activity, mostly due to the seasonal H3N2 virus, e.g., in northern China and Mongolia. However, the 2009 pandemic HIN1 virus (swine flu) has predominated in the Republic of Korea. Japan is reporting a sharp increase in flu-like illness activity.

Tropical Zone Countries -

Flu activity is most prominent in Asia. With a few exceptions, in the Americas and sub-Saharan Africa, there appears to be very little circulation of flu viruses. Madagascar, however, is reporting an increase in circulation of the seasonal H3N2 strain. In southern China, Singapore and Hong Kong, there is a high level of circulation of the 2009 pandemic H1N1 strain (swine flu).

Southern Hemisphere Countries -

There is very little flu activity in the southern hemisphere countries since they are in their summer season.

Travellers -

Travellers should be aware that the risk of exposure to flu is variable around the world. Travellers in areas where there is active circulation of seasonal or pandemic viruses should consider vaccination with the currently recommended flu vaccine. The World Health Organization has advised that the currently circulating flu viruses are the same viruses included in the 2010-11 flu vaccines for the northern hemisphere. The same viruses are included in the recommended vaccine for the 2011 southern hemisphere flu season.

Visit our Health Library for more information on exposure to and the prevention of Flu.

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