Health officials raised the alarm about a strain of swine flu that is resistant to the Tamiflu treatment as the virus claimed more lives on Tuesday, with Vietnam reporting its first fatal case.
India and South Africa both reported their first deadly cases of the A(H1N1) virus late Monday.
Maria Teresa Cerqueira, head of the Pan-American Health Organization office in La Jolla, California, said a Tamiflu-resistant mutation of A(H1N1) had been found around the US-Mexico border in El Paso and close to McAllen, Texas.
Experts had gathered in La Jolla, California, on Monday to discuss responses to the outbreak, and warned that resistant strains were likely emerging because of overuse of antivirals like Tamiflu.
"In the United States Tamiflu is sold with a prescription, but in Mexico and Canada it is sold freely and taken at the first sneeze. Then, when it is really needed, it doesn't work," said Cerqueira late Monday.
Cases of A(H1N1) that were resistant to the anti-viral medicine have now been found in the United States, Canada, Denmark, Hong Kong and Japan.
In Vietnam, officials reported the country's first swine flu fatality after a 29-year-old woman died from the disease in the southern coastal province of Khanh Hoa.
Nearly 1,000 people have been reported infected in Vietnam and about 500 of those are receiving hospital treatment, according to the health ministry.
In South Africa, authorities said a 22-year-old student at Stellenbosch University near Cape Town had died after contracting the virus, while in India a 14-year-old girl in the western city of Pune died.
With the world's highest number of HIV/AIDS-affected people -- nearly 19 percent of a 49-million-person population -- South Africa is considered particularly at risk because people with compromised immunity are more likely to fall prey to the disease.
South Africa's swine flu caseload has increased fourfold since the country's first case was reported on June 14.
In India, the government said that 2,479 people had been tested for swine flu so far out of whom 558 had tested positive for H1N1.
Some health officials in India have suggested a combination of climatic and meteorological factors -- such as high temperatures and humidity -- and social factors are likely to lower the risk of transmission there.
The virus continued to disrupt plans for public events.
The Russian state health agency warned football fans to stay away from the national team's World Cup qualifying tie with Wales in Cardiff on September 9.
"This would be an extremely unnecessary and inappropriate undertaking at a time of a flu epidemic," the head of Russia's state health agency Gennady Onishchenko said, according to local news agencies.
Onishchenko expressed fears that "the expressions of emotion on the part of football fans involving intense shouting" could lead to the airborne transmission of the flu virus.
Russia has to-date been relatively unscathed by the pandemic, with just 55 confirmed cases.
In China, the government decided to cancel summer camps in affected areas after recent outbreaks sickened children, parents and teachers, state media said Tuesday.
Student activities such as summer camps should be held "only when necessary," and in areas with a high incidence of A(H1N1), they should not go ahead at all, the China Daily reported, citing the health ministry.
China has reported a total of 2,152 cases of swine flu, but no deaths so far, according to the paper.
Experts remain puzzled as to why different countries have not always been affected to the same degree, with England and Scotland both heavily hit proportionately, yet neighboring France's tally appearing light by comparison.