Many epidemiologists have pointed out that, in reality, millions of people have had swine flu, usually in mild form, so the numbers of laboratory-confirmed cases were actually meaningless. And performing the tests has overwhelmed many national laboratories.

But the cases  and, more to the point, the deaths  have been closely watched by the media and flu experts, even those who knew they were undercounts, as a crude measure of how the epidemic spread around the globe. Such figures can also, in theory, be useful to public health officials. For example, knowing that Chile has had far fewer deaths than Argentina even though their outbreaks began almost simultaneously could be useful to other countries who might want to imitate Chile’s response.

The briefing note said countries would still be asked to report their first few confirmed cases. It also said countries should watch for clusters of fatalities, which could indicate the virus had mutated to a more lethal form. Other “signals to be vigilant for,” it said, were spikes in school absenteeism and surges in hospital visits.

Wealthy countries routinely collect such data, and also do blood tests to see what percentage of a population has flu antibodies, indicating they were infected but recovered. However, poor countries do not.

Dr. Joseph S. Bresee, chief of epidemiology for the C.D.C.’s flu division, said he agreed with the W.H.O. premise that case counts were just too inaccurate to keep using.