H1N1 matches seasonal flu peak months early -CDC

* Pandemic hits peak comparable to seasonal winter flu

* 1,000 killed in U.S., 20,000 hospitalized

WASHINGTON, Oct 23 (Reuters) - H1N1 swine flu has become widespread in 46 of the 50 U.S. states, a level comparable to the peak of ordinary flu seasons but far earlier and with more waves of infection expected, a top U.S. health official said on Friday.

“Forty-six states having widespread transmission is the peak of flu season. To be basically in the peak of flu season in October is extremely unusual,” said Dr Thomas Frieden, the director of the U.S. Centers for Disease Control and Prevention.

Frieden said seasonal flu normally peaks sometime between late November and early March. And he noted that this virus was sickening young adults and children as opposed to seasonal flu, which usually hits people over 65 the hardest.

“We expect that influenza will occur in waves and we can’t predict how high, how far or how long the wave will go or when the next will come,” he told reporters in a telephone briefing.

Swine flu has killed more than 1,000 Americans and put more than 20,000 in the hospital in the United States since it emerged earlier this year, Frieden said.

But health officials are quick to note that the actual number of cases cannot be measured. “We have had up until now many millions of cases of pandemic influenza in the U.S. and the numbers continue to increase,” Frieden said.

In a separate statement on Friday, the World Health Organization reported more than 414,000 laboratory confirmed cases of H1N1 worldwide, with nearly 5,000 deaths.

But the Geneva-based health agency noted that the figures were only the tip of the iceberg.

“As many countries have stopped counting individual cases, particularly of milder illness, the case count is significantly lower than the actual number of cases that have occurred,” WHO said.

Frieden said swine flu manufacturers have produced 16.1 million doses of vaccine, and as of Wednesday, 11.3 million doses had been shipped to U.S. states.

The U.S. government initially expected to have 40 million doses of vaccine available by the end of October but last week cut that projection by 25 to 30 percent, saying production problems would limit the October supply to 28 million to 30 million doses.

“Vaccine production is much less predictable than we wish. We are nowhere near where we thought we’d be by now. We are not near where the vaccine manufacturers predicted we would be,” Frieden said.

Much of the vaccine currently available is a nasal spray from AstraZeneca's AZN.L unit MedImmune.

The Obama administration has ordered vaccine from five manufacturers: Sanofi-Aventis SA SASY.PA, CSL Ltd CSL.AX, Novartis AG NOVN.VX, GlaxoSmithKline GSK.L and AstraZeneca's MedImmune. (Reporting by David Morgan; Editing by Maggie Fox and Eric Beech)