Originally published in MedPage Today
by Michael Smith, MedPage Today North American Correspondent
In the first six months of the H1N1 flu pandemic, 22 million Americans fell ill from the virus, the CDC now estimates.
The estimates are higher than initial counts, which included only laboratory-confirmed cases, Schuchat told reporters in a news conference.
“For influenza it’s virtually impossible to find every case with a lab test,” she said. “These estimates give a bigger picture of what’s going on.”
“Things haven’t really changed from last week to this week,” Schuchat said, “but we just feel that we’re finally able to update the public about how big a toll this virus is having so far.”
“Unfortunately I do expect all of these numbers to rise,” she added.
Particularly striking is the estimate of children who have died — some 540 — which contrasts with the 129 confirmed cases reported last week by the agency.
Schuchat said the apparent jump is the result of adding in children who died outside the healthcare system, were not diagnosed with the flu, or whose tests showed an unsubtyped strain of flu.
The new number is a “better estimate of the big picture of what’s out there,” she said.
For these estimates, she said, the CDC began with data from the Emerging Infections Program (EIP), which conducts surveillance for laboratory-confirmed flu-related hospital stays in children and adults in 62 counties covering 13 metropolitan areas in 10 states.
Those figures were extrapolated to the entire U.S. and then corrected for missing data, including people who did not seek care or were not diagnosed with H1N1 when they did, Schuchat said.
In some cases, a flu diagnosis is made, but a subtype can’t be assigned, she said, while in other cases the primary diagnosis may be bacterial pneumonia and no flu test will be done.
The estimates give a range of possible numbers, Schuchat said. For instance, the total number of cases, according to the estimates, ranges from 14 million to 34 million between April and Oct. 17.
The estimated hospital stays range from 63,000 to 153,000, while the number of deaths ranges from 2,500 to 6,100, she said.
The agency also broke its estimates down by age group and found that most cases occurred in those under 65:
* For children under 18, there were an estimated eight million illnesses, 36,000 hospital stays, and 540 deaths.
* For adults from 18 through 64, there were 12 million cases, 53,000 hospital stays, and 2,900 deaths.
* For those 65 and older, there were 2 million cases, 9,000 hospital stays, and 440 deaths.
Schuchat said the new estimates reinforce the value of the H1N1 vaccine and also the CDC’s recommendation that younger people get the vaccine first.
She added that about 41.6 million doses of the H1N1 vaccine are now available or have been distributed. That is less than officials had hoped, she said.
The seasonal flu vaccine distribution has now reached 94 million doses, up from 91 million last week, and manufacturers have told the CDC that 114 million will be shipped by the end of the year, Schuchat said.
The CDC is still suggesting that people get both vaccines, she said.
In the Nov. 13 issue of Morbidity and Mortality Weekly Report, the agency is reporting that — as previous data have suggested — there’s no protection against H1N1 to be found in the seasonal vaccine.
In a case-cohort analysis, the CDC found that the trivalent seasonal flu vaccine’s effectiveness against H1N1 was minus 10%.
Along with other evidence, the agency reported, the results “do not support an effect of seasonal 2008-2009 trivalent influenza vaccine in either decreasing or increasing the risk for pandemic influenza A (H1N1).”