Mexico City reemerges from H1N1 threat

As U.S. health authorities told Congress on Wednesday that they were prepared to mass produce a vaccine against the new H1N1 influenza virus if needed, World Health Organization officials said they would convene an expert committee next week to determine if such production was necessary -- or desirable. The U.S. is expected to follow the recommendation.

Production of a vaccine against the virus in anticipation of its return in the fall might sound like an obvious step, but doing so would sharply limit the amount of seasonal flu vaccine that would be available because the new vaccine would be manufactured instead of the traditional one.

The virulence of the new strain remains unclear, but seasonal flu is a known killer. About 36,000 people die from it in the U.S. each year and tens of thousands more worldwide.

“We would not want to have no seasonal influenza vaccine,” said Dr. Marie-Paule Kieny, director of the WHO Initiative for Vaccine Research, at a Geneva news conference.

She said the 20 influenza vaccine manufacturers worldwide had an annual production capacity of about 900 million doses of seasonal flu vaccine, and that might be stretched to as many as 2 billion doses of H1N1 vaccine. But that would mean abandoning the production of seasonal vaccines in plants that switched to the new vaccine.

She also said many questions remained about the production of an H1N1 vaccine, including how fast the virus would grow in the eggs used as a production medium, what size dose would be required and whether one dose would suffice.

Because the new virus is so different from circulating strains, and the general public has had no previous exposure to it, many experts think a booster shot will be necessary in addition to the vaccination. Such a booster is not needed with the traditional vaccine because of residual immunity from previous years.

If it becomes necessary to give two doses, that will sharply reduce the number of people who can be immunized.

Dr. Anne Schuchat of the Centers for Disease Control and Prevention told Congress that researchers had carried out the preliminary phase of vaccine production more rapidly than expected, and “should we need to manufacture a vaccine, we can work toward that goal very quickly.”

As of Wednesday afternoon, more than 2,000 cases of H1N1 infection had been confirmed globally, with Sweden and Poland becoming the most recent countries reporting a case, bringing the tally to 24 nations.

In the U.S., 30 new cases in Arizona, 40 in Illinois and scattered infections elsewhere brought the total to 680 confirmed cases.

More details began to emerge about the first H1N1-related death of a U.S. citizen. She has been identified as 33-year-old Judy Trunnell, a teacher in Harlingen, Texas, just over the border from Mexico.

She died early Tuesday after being hospitalized April 19, according to Leonel Lopez, Cameron County’s epidemiologist. Trunnell was pregnant when she entered the hospital, and the baby was delivered by cesarean section after she fell into a coma.

Health officials said she had “chronic underlying health conditions,” but would not give further details and would not say whether her death was a direct result of the flu.

The only other fatality outside of Mexico was a Mexican toddler who died in a Houston hospital last week.

Dr. Richard Besser, acting director of the CDC, said at least 35 people in the U.S. had been hospitalized with H1N1 flu. The median age is 15, with a range of 8 months to 53 years. Seasonal flu normally strikes the elderly and the very young heavily, and officials are at a loss to explain this virus’ different age distribution -- one that has been observed in Mexico as well.

One possibility is that the elderly retain some vestige of immunity from contact with swine flu viruses that circulated two to four decades ago.

Also Wednesday:

* As 136 Mexican nationals who had been quarantined in China returned home on an Aeromexico airliner, Chinese officials said they would release 28 students and a professor from the University of Montreal who had been held in quarantine in Changchun since Saturday. None of them displayed any symptoms of infection.

* Haiti turned away a Mexican aid ship carrying 77 tons of rice, fertilizer and emergency food kits. Mexican officials said the navy ship’s crew had been screened and showed no signs of infection, but the Haitian government requested that it come “on another occasion.”

* The WHO issued new cautions about pigs, seemingly contradicting earlier statements that it was safe to consume pork from infected animals.

“Meat from sick pigs or pigs found dead should not be processed or used for human consumption under any circumstances,” Jorgen Schlundt, director of the WHO’s Department of Food Safety, Zoonoses and Foodborne Diseases, told Reuters.

But he conceded that there was no data available about the survival of the virus on meat or on the infectious dose for humans.

Paul Sundberg, vice president of science and technology for the National Pork Board in the U.S., said Schlundt was technically correct, but added that rules already prevented meat from sick pigs or those found dead from entering the food system.

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thomas.maugh@latimes.com