The number of people infected with the influenza A(H1N1) virus has topped 2,000, the United Nations health agency confirmed Thursday, stressing that although symptoms for the vast majority of the cases are mild, there is no room for complacency.

The World Health Organization (WHO) noted that its international pandemic alert remains at phase 5, on a 6-level warning scale, as the number of laboratory confirmed cases rises to 2,099 – up by 441 from Wednesday – including 44 deaths.

As of 06:00 GMT Thursday, 23 countries reported influenza A(H1N1) infection, with Mexico containing 1,112 cases and 42 deaths, and the United States verifying 642 cases and 2 deaths.

“We continue to see human-to-human transmission – community level transmission – primarily in North America,” said WHO assistant director-general Keiji Fukuda at the agency’s daily update in Geneva.

“We are not seeing it yet anywhere else,” he said, explaining the decision to maintain the pandemic alert level at phase 5.

Mr. Fukuda warned that the situation is still evolving and “we really don’t understand how things are going to go in the future.”

Important questions remain over the spread of the flu from the northern hemisphere and whether it will become more dangerous over time than it is now. If the outbreak were to hit pandemic proportions, it would be reasonable to estimate a third of the world’s population would be infected, warned Mr. Fukuda.

Even when on an individual basis, illness for most people is relatively mild, if the numbers of infected are multiplied on a pandemic scale, the number of deaths will increase, he cautioned.

WHO also reiterated that people have not been infected by the influenza A(H1N1) virus through eating processed pork or other food products derived from pigs.