Only one dose of vaccine is needed for protection against pandemic H1N1 flu and the jabs have so far proved to be safe, the World Health Organisation has said.

Health experts have been debating whether one or two shots are necessary to protect against H1N1, known as swine flu. The number of doses required is key to estimating how many vaccines are needed in total.

The WHO has repeatedly sought to reassure people around the world that the H1N1 vaccines being made by 25 different companies, with various formulations, are safe.

'All the reports received to date following vaccination -- either in clinical trials or in mass vaccination campaigns -- have shown that the safety profile of these pandemic vaccines is good and is very similar to the one which is known for seasonal influenza vaccine,' said WHO expert Marie-Paule Kieny.

'Nothing special in terms of adverse events has been noted,' Kieny, who heads the UN health agency's vaccine research, told journalists on a telephone conference.

Safe, single dose

Earlier this week, its Strategic Advisory Group of Experts on Immunisation (SAGE) examined vaccines for H1N1, which tends to affect teenagers and young adults most.

A statement from the Geneva-based WHO said the SAGE experts had found no signs of unusual 'adverse events' -- the technical terms for severe complications such as illness or death -- from pandemic vaccines.

As a result, they said pregnant women, who are particularly vulnerable to H1N1, should be given the pandemic vaccines.

At least 5,712 people have died from confirmed cases of H1N1, WHO said in an update.

The SAGE committee recommended that a single dose of H1N1 vaccine should be used for adults and adolescents from age 10.

It said more studies were needed on the effectiveness of vaccines in children aged up to 10 years. Where national health authorities have made children a priority for vaccination, they should aim to vaccinate as many children as possible with a single dose, the group concluded.

The recommendation corresponds to WHO's estimate earlier this month that one dose suffices. Last week Europe's drug watchdog said two doses would be preferable.

In its statement, the WHO said 1 to 10 per cent of patients who developed a serious illness needed hospital treatment. Of those, 10 to 25 per cent needed treatment in an intensive care unit and 2 to 9 per cent died.

Very young children are most likely to require hospital treatment for the flu strain.

The WHO declared H1N1 an unstoppable global pandemic in June. Kieny said it could still make sense for countries to close schools, as Ukraine has done after its first confirmed swine flu death, to slow the spread of the virus.

In most cases, the WHO said is safe to administer vaccines for H1N1 and regular seasonal flu together, but not when both were 'live attenuated' vaccines such as nasal sprays.

WHO guidance on H1N1 vaccination is seen as pivotal for the pharmaceutical industry's investment decisions as well as government policies on purchasing and distributing vaccines.

Earlier this week GlaxoSmithKline said it would get a boost from H1N1 vaccine sales this year. And Sanofi-Aventis raised its outlook for 2009 saying the swine flu vaccine could add about $500 million to its sales in the fourth quarter. – Reuters