The number of swine flu deaths increased 264 from a week earlier, according to WHO. (CBC)

Nearly 5,000 people have reportedly died from swine flu since it emerged this year and developed into a global epidemic, the World Health Organization said Friday.

Since most countries have stopped counting individual swine flu cases, the figure is considered an underestimate.

WHO said there were 4,999 total deaths through Oct. 18, most of them in the Western Hemisphere. The figure increased 264 from a week earlier.

Donald Low, the medical director of Ontario's public health laboratories, told CBC News on Thursday that the number of serious cases has increased sharply in recent weeks.

The last available figures, which combine data until Oct. 10, show a total of 1,541 hospitalized swine flu cases across Canada. There have been a total of 86 swine flu-related deaths since the spring, including three new fatalities reported in Ontario between Tuesday and Thursday, according to the Public Health Agency of Canada.

Iceland had its first swine flu death this week, and WHO said Sudan and Trinidad and Tobago also reported deaths from the virus for the first time this week.

In London, drug maker GlaxoSmithKline PLC said children may only need one shot of its swine flu vaccine to be protected.

In its statement Friday, Glaxo said one dose was enough to boost children's immune systems to fight the virus, based on data from a trial in Spain in 200 children aged six months to 3 years.

Glaxo's finding comes after experts said they expected children would need two doses, since their immune systems are weaker than those of adults. Last week, rival vaccine maker Sanofi Aventis said children would likely need two doses of vaccine against swine flu, or H1N1.

GlaxoSmithKline's Pandemrix vaccine contains an adjuvant, a chemical compound that stretches a vaccine's active ingredient and increases the human body's immune response. While European flu vaccines commonly use adjuvants, there is limited data on how safe they are in groups including children and pregnant women.

No adjuvants in U.S.

The adjuvant in Glaxo's swine flu vaccine has been used in more than 41,000 people in bird flu, swine flu and regular flu vaccines.

Swine flu vaccines in the U.S. do not have adjuvants. Some countries, such as Canada, have ordered special stocks of vaccines without adjuvants for their at-risk populations.

While most people recover from swine flu without needing medical treatment, the virus strikes children particularly hard.

According to data from the U.S. Centers for Disease Control and Prevention, more than half of hospitalizations and nearly a quarter of deaths due to swine flu are in children and adults under 25.

An Associated Press-GfK poll found that a third of American parents don't want their children to get the swine flu shot, with many citing concerns about side-effects.

Of the thousands of people who have so far received the swine flu vaccine, the most commonly reported side-effects have been soreness where the injection was given and minor flu symptoms.

On Thursday, New York state health officials suspended a ruling that would have forced health care workers across the state to get vaccinated against the swine flu by the end of November or risk losing their jobs. The decision was made because the vaccine is in short supply in the U.S., they said.

With files from The Associated Press