People wearing masks walk on a street in Tokyo, Japan, on May 19. (XINHUA)

The A/H1N1 influenza virus has caused a total of 9,830 human infections in 40 countries, including 79 deaths, the World Health Organization (WHO) said in a latest update on Tuesday.

The United States, Mexico and Canada have continued to report the largest numbers of laboratory confirmed infections, with 5,123; 3,648 and 496 cases respectively. But most of the deaths have occurred in Mexico, where the new virus was first identified.

Other countries that have been hit hard by the new virus include Spain,Britain and Japan, which have reported 103, 102 and 159 cases respectively.

So far most of the cases outside Mexico have been mild. But the WHO has warned repeatedly that the severity of the disease might increase because of the intrinsic mutability of the flu virus and other unknown factors.

"This virus may have given us a grace period, but we do not know how long this grace period will last. No one can say whether this is just the calm before the storm," WHO Director-General Dr. Margaret Chan said on Monday.

"The emergence of the new virus creates great pressure on governments, ministries of health, and the WHO to make the right decisions and take the right actions at a time of great scientific uncertainty," Chan told health ministers attending the 62nd World Health Assembly.

(Xinhua News Agency May 19, 2009)