Tuesday, November 24, 2009

U.S. Flu Decline Confirmed

The CDC is reporting a decline in U.S. flu cases. The CDC’s numbers are potentially misleading, but are confirmed by other measures. It is now safe to say the H1N1 flu really did peak in August.

The CDC’s measures can be misleading, as they are mainly influenced by the number of doctor visits, which in turn are strongly affected by the hype surrounding the flu. Health authorities engineered an avalanche of media reports about flu at the end of September and in the first half of October to try to persuade people to get the H1N1 flu vaccine. The scare tactics worked. They also scared lots of people into thinking they had the flu, and when they went to the doctor, many got tested, and sure enough, nearly half of them did have the H1N1 flu. The spike in flu cases confirmed during that period does not indicate a spike in flu during that time, though, just an increase in testing, as other measures showed flu at a much lower level than during its August peak.

The flu hype certainly faded as we went into November, so the decline reported by the CDC also has to be taken with a grain of salt. Yet the picture coming from the CDC of a substantial decline in flu this month is probably true because it matches other measures, based mostly on self-reporting. These show a total rate of flu barely half that of late September and October, and perhaps a fifth of the rate of the second half of August and first few days of September.

According to one epidemiological estimate, based mostly on lab tests from people who appeared healthy, about 14 percent of Americans came down with H1N1 flu during the summer, and if I can extrapolate that, that would mean about 4 to 5 percent caught it in the fall — with most showing no more than vague, fleeting symptoms. The first wave, then, was over long before anyone could have produced a vaccine. The current fuss over the way the vaccine was produced and delivered is largely academic, at least in the United States.

Doctor-visit reports from Canada are still showing an increase in H1N1 flu, but remaining at a much lower level than seen in the United States. There, the vaccine probably did arrive before the flu peak.

There will be a second wave of H1N1 flu in the United States during the winter months, and probably again during the following winter, but the first wave was so large that any subsequent wave would have to be smaller — too small to notice, if we weren’t all looking for it.

Across the northern hemisphere, there are concerns about the spread of H1N1 flu, but the facts so far are not living up to the worst fears. This is particularly so with an epidemic in Ukraine in which more than one fourth of the population was thought to have come down with flu. The Ukraine epidemic is worrisome because of the number of deaths reported, even though tests so far suggest that most of the cases do not involve flu. This means that the problem is probably a different infectious disease. At this point, determining the cause and nature of the Ukraine illnesses ought to be a greater priority than the mop-up work remaining to be done for H1N1 flu.