Science tries to address concerns of edgy public

DALLAS — Top headlines about swine flu continue to be about the lack of vaccine. But behind the news is a daily trickle of new information about the H1N1 virus itself.

Since swine flu was first spotted last spring, thousands of researchers all over the world have been tweezing out the secrets of the pandemic.

What do we know now that we didn't know when the first swine-flu warnings were sounded in April?

The best news is it could be a lot worse. That has meant that although swine flu spreads easily, most people who get it suffer no more than a few days.

Here are some answers to H1N1 questions, based on the science of the moment:

Q: Why is the vaccine production going so slowly?

A: The manufacturers had bad luck when there was no room for a misstep, said Dr. James Luby, an expert on infectious diseases at the University of Texas Southwestern Medical Center in Dallas.

Making flu vaccine, Luby said, requires growing the virus in chicken eggs.

Some strains, even of the same kind of flu, grow faster than others.

For the seasonal flu, manufacturers may have time to adjust midstream.

But the need to get the H1N1 vaccine out in a hurry meant researchers had to take their best shot.

The strain that was chosen simply grows more slowly in vaccine production than most other flu viruses.

Q: Are we near the peak of this infection?

A: Nobody knows. What flu experts are really worried about is whether there will be another peak. In the 1917-1918 and 1957-1958 pandemics, illness was widespread in the fall, went away, then came roaring back in January.

This year's pattern of infection looks a lot like those earlier pandemics, Luby said.

Q: If I get the vaccine this year, will it protect me next year?

A: Maybe not, says Dr. Jeffrey Kahn, chief of infectious diseases at Children's Medical Center in Dallas and professor of pediatrics and microbiology at UT Southwestern.

"Next year's swine-flu vaccine may need to be a different strain than this year's," he said.

After all, new seasonal-flu vaccines are made every year. The viruses mutate enough to avoid the body's defenses that had been primed from the prior year's shot.

So far, H1N1 is not changing.

But as more people become immune — either through infection or vaccination — that will put genetic pressure on the virus to change, Kahn said.

Q: Why doesn't this flu follow the same seasonal pattern as most other flus?

A: Scientists don't really know why any flu has a particular season, so figuring out why this one is different is a real challenge.

Kahn and Luby think it has something to do with the fact that very few people had any immunity to this virus.

So what might have been a small cluster of offseason infections instead spread quickly.

Q: Why do the elderly seem to have resistance to the new H1N1 flu?

A: This flu is something like the 1957 pandemic flu. And something like the 1976 swine flu.

People who were young adults in 1957 seem to have some resistance to the new flu.

People who were around for the 1957 flu and got the 1976 flu vaccine appear to have even more resistance, Luby said.

Q: Why do a small number of otherwise healthy people get much sicker than most others who catch this flu?

A: Some of the worst cases are easy to understand: People with other health problems are more vulnerable. The risk to pregnant women is harder to explain, but may be related to hormonal changes to the immune system or breathing constrictions in the third trimester. More mysterious still are the otherwise healthy people who get very ill.

Kahn thinks that some people have a genetic weakness to this particular virus that doesn't show up in any other way — an invisible pre-existing condition.

Luby blames some of the worst illness on the fact that some people carry colonies of microbes around without any illness. The flu infection damages the lungs and gives otherwise asymptomatic pneumonia and MRSA bacteria a place to grow.

But viruses are too tricky for any pat answer. "If you take identical twins and expose them to the same virus, sometimes you have very different clinical outcomes," Luby said.