WASHINGTON (Reuters) - The United States now has 642 confirmed cases of the new H1N1 flu, with two deaths, the Centres for Disease Control and Prevention reported on Wednesday.
And officials are puzzled because most of the 35 people who have been hospitalized with the new swine flu are young — 53 and younger.
However most cases are mild and work is going ahead on a new vaccine, although it is not clear if one will be offered in the autumn.
“We are reporting 1,487 probable and confirmed cases in 44 states,” CDC acting director Dr. Richard Besser told a news briefing. People of all ages have been infected but 58 percent of the cases are among people 18 and younger — not the pattern seen with seasonal flu, which tends to attack the elderly.
CDC officials have said they expect the new swine flu to spread to all 50 states, to cause severe disease and some more deaths, although most cases have been mild. Two people have died in the United States.
Mexico has confirmed 42 deaths and said it was impossible to get samples from about 70 more people who died of flu-like illness recently. Globally, more than 1,600 cases have been reported in 23 countries.
“The hospitalized patients are younger than what you see with seasonal flu,” Besser said. “That is something we are keeping an eye on.”
It is not clear whether this has to do with the ages of people who travelled to Mexico, or might indicate that older people have some protection against the new strain.
Besser said seven out of 13 of the patients who have details available had underlying disease that would make them more likely to have serious symptoms.
On Tuesday, the confirmed U.S. cases of H1N1 stood at 403.
Many of the newly reported cases in Mexico and the United States come from a backlog of samples awaiting testing, but Besser said now that new test kits have been distributed to all U.S. states and 16 countries, reporting of new cases should pick up.
The World Health Organisation is waiting to see if more cases turn up in Europe or Asia before declaring a full pandemic. The current phase of pandemic alert is a 5.
“For WHO to move from a level 5 to a level 6 they would look to see if there is sustained transmission of a virus in more than one WHO region,” Besser said.
“With the number of cases in other countries, I would be surprised if we don’t get to a level 6.”
Besser said officials are debating whether a new vaccine is needed against the strain.
It is possible a separate vaccine could be formulated and offered, Besser and WHO officials say. Tests would be needed to know if people would need one or two doses, Besser said.
But Dr. Gregory Poland, director of the vaccine research group at the Mayo Clinic in Rochester, Minnesota, said the new virus is distinct enough that a priming dose would be needed for many people.
“It would almost certainly take two doses in younger people. I think what is unknown is whether it would take two in older adults or just one,” Poland said in a telephone interview.
Additional reporting by Julie Steenhuysen in Chicago; editing by Mohammad Zargham