Swine flu is starting to taper off along with the influenza season in the Southern Hemisphere, but it has killed at least 36 U.S. children, U.S. officials reported on Thursday.

Two companies working on vaccines against the new H1N1 virus said they gotten a good immune response in some volunteers with just a single dose of vaccine, but flu experts were skeptical about the limited results.

The reports will help countries in the Northern Hemisphere plan for a resurgence of the pandemic as temperatures cool and schools return from summer breaks, officials said.

The U.S. government said an analysis of the epidemics in Australia, Argentina, Chile, New Zealand, and Uruguay showed that while H1N1 dominated the flu seasons there, it was only moderately severe.

“All countries report that after mid-July, disease activity in most parts of the country decreased,” according to the report published at http://www.flu.gov.

“This indicates that the duration of the current influenza season in the Southern Hemisphere, in which the 2009 H1N1 virus is the predominate strain, may be similar in length to an average seasonal influenza season.”

The pandemic did stress healthcare systems, but not for long, the report said.

“All five countries reported early regional surges in hospital, emergency department and outpatient visits. Some countries reported transient hospital bed, equipment or medication shortages,” the report reads.

In a separate report, the U.S. Centers for Disease Control and Prevention reported that 36 American children had died of the new H1N1 flu since it was identified in April.

It said 67 percent of them had medical conditions putting them more at risk of severe disease, such as asthma, or were disabled with conditions such as cerebral palsy, but 22 percent of the children were under 5 and healthy.

Children who did not have an underlying condition and who did become severely ill were often suffering from secondary bacterial infections, the CDC said.

CDC Director Dr. Thomas Frieden said it was important to identify and promptly treat children at special risk of complications from any flu, especially children with chronic conditions or a child that appears to have trouble breathing.

VACCINE SUCCESS

In Zurich, Novartis AG reported that a single dose of its Celtura H1N1 vaccine, boosted with an immune-stimulating compound called an adjuvant, produced desired effects in 80 out of 100 volunteers.

The World Health Organization said if this was borne out in larger studies, it might help stretch a limited vaccine supply.

In Beijing, China’s Sinovac Biotech said it had received approval from China’s State Food and Drug Administration for its vaccine, which Sinovac says needs only one 15 microgram dose to be effective.

Frieden said he would like to examine the data from both trials. Most studies so far have suggested that because many people lack any immunity to the new virus, they will need two doses to be fully protected from infection.

He noted that the five vaccines approved for the U.S. market do not use adjuvants and that trials in people are still going on to see which dose would work best.

“The good news is that so far, everything that we’ve seen, both in this country and abroad, shows that the virus has not changed to become more deadly. That means that although it may affect lots of people, most people will not be severely ill,” Frieden told reporters in a telephone briefing.

The U.S. Institute of Medicine released a report recommending the use of special masks called N95 respirators for healthcare workers treating people with suspected H1N1 flu, but also saying much more research is needed into how flu spreads.

A N95 respirator covers the nose and mouth tightly, filtering out tiny particles that can carry viruses and bacteria. Research suggests that surgical masks, commonly worn in Mexico during the height of the pandemic, do little to protect the wearer.

And a survey commissioned by the U.S. Meat Export Federation showed that nearly two-thirds of consumers in China, the world’s largest pork producer and consumer, stopped eating pork in the early stages of the pandemic.

The survey of 1,200 Chinese consumers also showed that more than one in five Chinese consumers still wrongly believe that eating pork can result in catching the flu virus.

U.S. pork exports to China for June, the latest month available, totaled 1.861 million pounds, down from 3.161 million pounds in May and down sharply from 69.623 million in June 2008, when exports to China soared ahead of the summer Olympics.

By Maggie Fox, Health and Science Editor
WASHINGTON (Reuters)