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Because people can catch the new H1N1 swine flu by inhaling the virus, health-care workers who deal with flu patients should wear properly fitted N95 disposable respirator masks, a new report from the Institute of Medicine advises.

These masks are not the same as loosely fitted surgical masks. N95 respirators fit tightly around the mouth and nose and have filters that can block about 95 percent of the flu virus, according to the report released Thursday.

“The U.S. Centers for Disease Control and Prevention guidelines for protection of health-care workers during an H1N1 outbreak have been that those in close contact with people who have H1N1 flu should wear N95 respirators,” said Dr. Kenneth I. Shine, chair of the Committee on Respiratory Protection for Healthcare Workers in the Workplace Against Novel H1N1 Influenza A.

The Institute evaluated the effectiveness of N95 respirators and medical masks in protecting wearers from the H1N1 flu at the request of the CDC and other government agencies.

“We saw a fair amount of evidence that suggests that this virus can be transmitted through the air,” said Shine, who is also executive vice chancellor for health affairs at the University of Texas. “How much of transmission is due to that is still an unproven issue and needs a lot of research.”

Shine noted that the virus is also transmitted by person-to-person contact and by contact with surfaces that have been exposed to the virus. Hence, the advice to wash hands often.

Tests showed that the protection provided by N95 masks was eight to 12 times greater than that offered by surgical masks, the report said.

In addition, tests of surgical masks show wide variations in protection. They can filter from 4 percent to as much as 90 percent of the virus, but there is no way of controlling leakage around the edges of the mask, Shine said.

“Surgical masks were not designed to protect people from airborne infection, and they are not likely to be effective, whereas N95 respirators have a much better ability to protect health-care workers,” he said.

Based on these findings, the report recommends that health-care workers should use N95 respirators. Because a tight seal is so important, they should be individually fit-tested, it said.

The N95 respirators are not a perfect solution, however. “We are aware that there are shortages of these respirators,” Shine said. Also, some health-care workers, particularly anyone with heart or lung disease or other health conditions, could find it difficult to breathe through a respirator mask. Those people “should talk with your doctor before using a respirator,” the CDC says.

The N95 face masks cost $10 to $20 a box depending on the manufacturer and the model. Like surgical masks, they should “be worn only once and then thrown away,” the agency says.

While not advising surgical masks for health-care workers, Shine said he would like to see flu patients wear them. “There, the principal affect is to decrease droplet spread from sneezing and coughing,” he said.

Another expert said the general public shouldn’t rush to buy either type of mask to protect them from the H1N1 flu.

“Surgical masks are not effective and will only spread panic,” said Dr. Marc Siegel, an associate professor of medicine at New York University Langone Medical Center in New York City. “Only people with flu should use them.”

“Health-care workers in direct contact with flu patients should use N95 respirator masks,” Siegel added. “They are the most effective, but are not for general use.”

Because it is still unclear what proportion of influenza cases gets spread by airborne particles, the report called for more research on flu transmission. More cooperation among three government agencies — the U.S. Food and Drug Administration, the U.S. Occupational Safety and Health Administration and the CDC’s National Institute for Occupational Safety and Health — in evaluating and recommending protective masks is also warranted, Shine said.

Dr. Pascal James Imperato, dean and distinguished service professor of the School of Public Health at the State University of New York Downstate Medical Center in Brooklyn, agreed with the recommendations “based on current scientific knowledge.”

Also, the call for more research on the routes of flu transmission will benefit the general public, he said.

The discovery of immune system particles that attack the AIDS virus may finally open a way to make a vaccine that could protect people against the deadly and incurable infection, U.S. researchers said on Thursday.

They used new technology to troll through the blood of 1,800 people infected with the AIDS virus and identified two immune system compounds called antibodies that could neutralize the virus.

And they found a new part of the virus that the antibodies attack, offering a new way to design a vaccine, they reported in the journal Science.

“So now we may have a better chance of designing a vaccine that will elicit such broadly neutralizing antibodies, which we think are key to successful vaccine development,” said Dennis Burton of The Scripps Research Institute in La Jolla, California, who led the study.

“The findings themselves are an exciting advance toward the goal of an effective AIDS vaccine because now we’ve got a new, potentially better target on HIV to focus our efforts for vaccine design,” added Wayne Koff of the International AIDS Vaccine Initiative, or IAVI, which sponsored the study.

Since the AIDS pandemic started in the early 1980s, more than 25 million people globally have died from the virus. The World Health Organization estimates that 33 million are currently infected.

There is no cure, although a cocktail of drugs can help keep the virus under control. Efforts to make a vaccine have failed almost completely.

MUTABLE VIRUS

Part of this is because the virus mutates so much that any one person is infected with millions of different versions, each one appearing different to the immune system.

In addition, the virus infects the very immune cells that are supposed to help protect the body. And if even one virus gets past the immune defense, it appears to set up a lifelong infection. No drug has been able to eradicate it.

IAVI director Dr. Seth Berkley said the findings will not lead directly to a vaccine, but show that there are new and better ways to design one.

He said 10 percent of the patients whose blood was screened had a strong antibody response to the virus. “We have people with even more potent serum out there. We will probably see more,” he said in a telephone interview.

It may also be possible to use such antibodies as therapy themselves — such as the gamma globulin used for hepatitis virus. But the eventual goal, Berkley said, is a vaccine that produces antibodies that could stop the virus from ever infecting a person in the first place.

“We haven’t been able to do that because we haven’t been able to find the right kind of response,” Berkley said.

Most vaccines elicit an antibody response, priming the body to make antibodies that will recognize and attack an invader such as a bacteria or virus.

The two antibodies, called PG9 and PG16, are the first new HIV antibodies to have been identified in more than 10 years. They target a region of the spike the virus uses to infect cells, the researchers wrote.

A team at South San Francisco-based Monogram Biosciences Inc screened the blood for the ability to neutralize HIV. Theraclone Sciences used its technology to identify the antibodies involved.

North Carolina-based Laboratory Corp of America Holdings acquired Monogram in July.