Officials from the US Centers for Disease Control and Prevention (CDC) said on Tuesday that more than half of Americans hospitalized with the new H1N1 swine flu are under 25, and nearly a quarter of deaths are among that age group, revealing a pattern that is quite different to seasonal flu.

Director of CDC’s National Center for Immunization and Respiratory Diseases, Dr Anne Schuchat, told the media that with seasonal flu they would expect to see about 60 per cent of hospitalizations being people aged 65 and over, but figures from 27 states show that 53 per cent of hospitalizations with H1N1 are people under 25 and only 7 per cent are people aged 65 and over.

According to Reuters news agency, Schuchat stressed that the figures were incomplete, but it was unlikely that the complete picture is much differenet and if anything she expects the current figures to underestimate the extent of the pandemic.

Calling H1N1 swine flu “a disease of the young”, Schuchat said that deaths to the virus were reflecting a similar higher percentage of young people. Of the 292 deaths reported from 28 states, nearly a quarter were people under 25 years of age, and 65 per cent were people aged 25 to 64, with just 12 per cent being people over 65.

In a normal year of just seasonal flu the vast majority of deaths, about 90 per cent, are among those over 65, she said.

Experts are suggesting that the reason H1N1 is affecting young people more severely is because senior citizens are more likely to have been exposed to a swine-related flu in the past and have some residual immunity that offers some protection agains the current strain. Young people have no such memory in their bodies and are thus more vulnerable.

The CDC’s flu situation update late last week showed that 41 states are now reporting widespread influenza activity, and said that so many reports of widespread activity was “unprecedented during seasonal flu”.

However, Schuchat said the picture is becoming less clear because as the cooler weather sets in, other viruses that cause flu-like symptoms such as cough, sore throat, fever, aches and pains, are emerging. She said about 30 per cent of people with flu-like symptoms are being diagnosed with flu, nearly all of which is H1N1 rather than seasonal flu.

Schuchat said the percentage of people with H1N1 is probably higher than this because tests often miss cases of H1N1, reported Reuters.

The CDC is urging the use of antivirals like Tamiflu for people who get really ill with swine flu, or who have underlying medical conditions or who are pregnant.

According to a report in the Los Angeles Times, Schuchat told the press that doctors should give the antiviral if they have a patient in one of these groups whom they suspect of having flu.

“We don’t want to wait for laboratory confirmation,” she said, emphasizing that the tests can also give a false negative and doctors should not be fooled by this.

If your patient is sick, “don’t believe a negative rapid test,” said Schuchat.

Meanwhile vaccine supplies are slower than the government was expecting, with so far only 12.8 million doses available for states to order: the federal authorities were hoping there would be 40 million available by the end of the month, reports the Wall Street Journal.

Schuchat said that while vaccine availability was increasing daily, she acknowledged that current stocks are not enough to meet demand and that there is also a shortage of seasonal vaccine in some places.

Sources: CDC, Reuters, Los Angeles Times, Wall Street Journal.

Written by: Catharine Paddock, PhD