The number of confirmed cases of the new influenza A (H1N1) has climbed to 6,497, including 65 deaths, the World Health Organisation said on Thursday.

The number of countries reporting confirmed cases remains at 33, with the vast majority of cases in Mexico and the United States, the WHO said in a twice-daily update.

The latest update appeared before a meeting of experts later on Thursday by the WHO to decide whether drugmakers should switch production of flu vaccine to deal with the new outbreak, widely known as swine flu, from seasonal flu.

Seasonal flu kills 500,000 people a year, mainly the elderly or those with respiratory problems like asthma.

So the WHO will want to be sure that the H1N1 outbreak poses a severe threat before recommending the switch.

Drugmakers do not have the capacity to make both. One question the experts will examine is whether a course against swine flu would require two shots rather than one, taking up twice as much manufacturing capacity.

Recommendations by the experts will be put to the WHO’s World Health Assembly next week. In the meantime manufacturers have already started producing the H1N1 vaccine.

The spread of the disease has led the WHO to declare a pandemic is imminent. On April 29 it raised its pandemic alert to 5 on a 6-level scale.

Evidence the new flu was spreading in a sustained manner in countries outside North America would trigger a move to phase 6 for a full-blown pandemic.

Conversely, signs the infection is not spreading in new countries and is slowing in North America could allow the WHO to lower the alert level.

Mexico’s Health Minister Jose Angel Cordova told Reuters the flu was infecting fewer people and was likely to cause no more than 100 deaths in the country.

WHO experts say it is not possible to create a scale giving a scientific assessment of the severity of the outbreak, on the lines of hurricane warnings or the Richter scale for earthquakes.

That is because the new flu affects people differently in various countries, depending on their stage of development, healthcare systems and experience in dealing with epidemics.

The WHO’s tally lags national reports but is considered more secure. Rising numbers can indicate that a backlog of cases is being processed, as well as the spread of the disease.

The WHO said Mexico has reported 2,446 confirmed cases including 60 deaths. The United States has reported 3,352 confirmed cases including 3 deaths. Canada has 389 confirmed cases and Costa Rica 8 cases, both with one death.

Other countries with confirmed cases but no deaths are Argentina (1), Australia (1), Austria (1), Brazil (8), Britain (71), China (4), Colombia (7), Cuba (1), Denmark (1), El Salvador (4), Finland (2), France (14), Germany (12), Guatemala (3), Ireland (1), Israel (7), Italy (9), Japan (4), Netherlands (3) New Zealand (7), Norway (2), Panama (29), Poland (1), Portugal (1), South Korea (3), Spain (100), Sweden (2), Switzerland (1) and Thailand (2).

(For a WHO map of the spread of cases, go to:

http://www.who.int/csr/don/h1n1_20090514_0800.jpg )

(For WHO information on swine flu, go to: http://www.who.int/csr/disease/swineflu/en/index.html )

GENEVA (Reuters)