* Genetic sequencing shows no virus mutation, WHO says
* Virus circulating widely, has killed at least 2,837
* Red Cross launches information campaign to avert deaths (recasts, adds annual toll from seasonal flu in new 9th para)
By Stephanie Nebehay
GENEVA, Sept 4 (Reuters) - The pandemic H1N1 flu virus continues to cause widespread infection in many parts of the world but is not becoming more serious, the World Health Organisation (WHO) said on Friday.
The WHO said it had counted 2,837 deaths worldwide but noted that not every case was being counted any more.
The United Nations agency is closely monitoring the strain, commonly known as swine flu, but said it had not detected any mutation which might signal that it has become more deadly.
"It is not causing more severe illness than before, there have been no changes in the behaviour of the virus," WHO spokesman Gregory Hartl told a news briefing.
"We are continuing to see increased number of deaths because we are seeing many, many more cases."
About a quarter of a million cases have been laboratory-confirmed worldwide, but this is far fewer than the true number according to the WHO which has stopped requiring its 193 member states to report individual cases.
Its previous update of Aug. 28 showed at least 2,185 deaths, meaning an additional 652 deaths were reported in the past week.
The virus could eventually infect 2 billion people, or a third of the world’s population, according to WHO estimates.
Every year, seasonal influenza kills between 250,000 and 500,000 people globally, it says. But H1N1 is causing a year-round flu season and may infect more people than a usual seasonal virus, potentially adding up to more deaths.
"In the best case scenario we have today, we will still have a moderate virus that is projected to cause several million deaths," Dr. Tammam Aloudat, senior health officer at the International Federation of Red Cross and Red Crescent Societies, told a separate news briefing.
"Which means that even in the best case scenario, we do have an emergency on our hands, an emergency of a scale different from what we have seen before in the modern era," he said.
The Federation, the world’s largest disaster relief network, on Friday launched an information campaign to help the poorest communities reduce infection through simple hygiene measures.
H1N1, declared a pandemic on June 11, causes many mild symptoms, but has killed more people with medical conditions, such as asthma, or pregnant women, who should be treated with the antiviral Tamiflu by Roche Holding AG ROG.VX, WHO says.
Tropical regions of many countries in South and Southeast Asia are reporting "increasing or sustained high levels of respiratory disease", although Thailand has reported a declining trend, according to the WHO’s latest weekly update.
In Latin America, countries including Ecuador, Venezuela, Peru and Brazil are reporting more respiratory disease, while outbreaks seem to have peaked in Chile and Argentina, it said.
Japan is seeing an early start to its regular flu season. In Canada and the United States, influenza activity remains "low overall", despite increases in the southeastern U.S. region.
Drugmakers are racing to develop vaccines amid experts’ warnings that a "second wave" of the virus is approaching as weather cools in the northern hemisphere and the traditional flu season starts.
On Thursday, Novartis AG NOVN.VX said a single dose of its vaccine might protect against the virus, raising hopes that potentially tight supplies could go further when mass immunisation starts this month. [ID:nL3450192]
Hartl has called the preliminary results "encouraging", noting any vaccine that can be administered in one dose would substantially increase the number of overall doses available. (Additional reporting by Laura MacInnis in Geneva and Maggie Fox in Washington; Editing by Janet Lawrence)