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Flu season reminders

HOUSTON -- (September 18, 2009) -- Although the seasonal flu and the H1N1 (swine) influenza virus are very similar in terms of symptoms and treatment, the main difference between the two is in age-related susceptibility, according to an expert at Baylor College of Medicine.

"Since many people have partial immunity to the seasonal virus, it does not generally spread in warm weather," said Dr. Paul Glezen, professor of molecular virology and microbiology and pediatrics at BCM.

Conditions that spread virus

The seasonal virus transmission is enhanced under three conditions – when the weather is cold (with low humidity), when children are in school and when people are in close spaces. When all three conditions are present, the virus spreads quickly.

Because everyone under 40 years of age is equally susceptible to the H1N1 virus, the virus has been able to spread in warm weather and when children are out of school.

Seasonal vaccine important

It's important to get the vaccination for the seasonal flu while waiting for distribution of the pandemic H1N1 vaccination, he said. Seasonal influenza vaccine may provide some cross protection against the new H1N1 virus for persons over 40 years of age.

"Fifty thousand Americans are killed by the seasonal virus each year," said Glezen. "Don't neglect getting the vaccination."

Lower mortality rate, higher transmission rate

The overall mortality rate is expected to be lower in the pandemic than the seasonal virus, but the infection rate will be higher in young adults and children. Therefore, the age specific mortality for younger age groups will be higher – perhaps much higher – during the novel A(H1N1) pandemic than during the seasonal epidemic, he said.

"It's a myth that it's too soon to get the seasonal flu vaccine," said Glezen. "It takes 10 to 14 days to take effect."

Plenty of vaccines available

Seasonal vaccine is available in adequate supplies and in convenient locations, he said. The pandemic A (H1N1) vaccine has been produced on contract to the U.S. government and will be distributed through the state health departments beginning in October.