GENEVA, Jan. 9 (Xinhua) -- People should consider vaccination as the primary intervention against influenza, as the northern hemisphere influenza season starts increasing in many temperate countries, a World Health Organization (WHO) expert advised on Tuesday.

Seasonal influenza is an acute respiratory infection caused by influenza viruses which circulate in all parts of the world. There are four types of seasonal influenza viruses, types A, B, C and D, of which influenza A and B viruses circulate and cause seasonal epidemics of disease.

Influenza A viruses are further classified into subtypes according to the combinations of the hemagglutinin (HA) and the neuraminidase (NA), the proteins on the surface of the virus. Currently circulating in humans are subtype A(H1N1) and A(H3N2) influenza viruses.

According to Dr. Zhang Wenqing, director of WHO Global Influenza Program, influenza vaccines, which have been used every year in the past dozens of years and for which the technologies are mature, are licensed by national regulatory agencies and safe. It's the primary intervention to reduce influenza morbidity and mortality, especially in risk groups.

She confirmed that people should consider influenza vaccines to protect themselves, even if the vaccine is not closely related to the predominant circulating virus at moment. As seasonal influenza vaccines include several different influenza viruses, even if one of the viruses is not closely related, the other viruses in the vaccine are likely to be closely related and therefore offer good protection.

In addition to vaccines, other personal protective measures against influenza should also include regular hand washing with proper drying of the hands, good respiratory hygiene such as covering mouth and nose when coughing or sneezing, early self-isolation of those feel unwell, feverish or having other symptoms of influenza, and avoiding close contact with sick people, said Dr. Zhang.

Currently the northern hemisphere influenza season starts increasing in many temperate countries. The death toll of seasonal influenza cases in United States, the number of states reporting widespread flu activity jumped from 23 to 36, while "widespread" means that more than 50 percent of geographic regions within the state are reporting flu activity; and in China, the authorities have said that predominant virus strains responsible for the flu outbreak this winter have been little seen in recent years.

According to a latest WHO report released in late 2017, up to 650,000 deaths annually are associated with respiratory diseases from seasonal influenza. The agency has already urged all countries to work together to control influenza outbreaks.