By Alison Young
The Atlanta Journal-Constitution
ATLANTA, Ga. — In the coming weeks, as hot and humid summer weather settles in, cases of swine flu are expected to slow significantly in Georgia and across the United States.
For reasons not clear to scientists, influenza viruses just don’t spread much during summer in parts of the world that have pronounced seasons.
“The whole question of seasonality is one that’s fascinated influenza researchers and the public alike,” said Dr. Nancy Cox, who heads the influenza division at the Centers for Disease Control and Prevention in Atlanta.
The change of seasons within weeks of scientists identifying the new 2009 H1N1 flu virus is good news for the United States, Mexico and other countries in the Northern Hemisphere. In the United States the flu season typically runs from October through April, with the cases usually peaking in February.
But in the Southern Hemisphere, which is heading toward its winter, the flu season is ramping up — just in time for the arrival of the new virus that people there have never been exposed to or vaccinated against.
Scientists around the world will be watching closely what happens and using the information to prepare for the swine flu’s expected return to the Northern Hemisphere and the United States in the fall.
Will swine flu become the dominant flu strain in the Southern Hemisphere, crowding out the other seasonal flu viruses? Does the severity of disease caused by the new virus increase or decrease? Does it develop resistance to antiviral drugs? Does the genetic makeup of the new virus change — and how will that affect its virulence and efforts to develop a vaccine before the flu season hits the U.S. next fall?
Experts said the answers to these questions are key to predicting what may happen here in the fall.
“During this period of time, between now and fall, is critically important to individual preparedness, the community preparedness and how the impact of this could be on our communities should this virus come back in a severe form,” Dr. Richard Besser, acting CDC director, said Thursday.
Besser noted that transmission of the swine flu virus continues in the U.S., and he strongly advised against people intentionally trying to expose themselves to it. There have been some reports nationally of people holding “swine flu parties” in the hopes that early exposure may provide later protection.
Besser encouraged the public to continue to wash hands, cover coughs and stay home when ill to slow the spread of the disease.
“Hopefully we’ll be aided by warmer weather,” he said.
Scientists aren’t sure why the spread of flu tends to be limited — though not eliminated — in the summer. Temperature and humidity may play a role, as may social conditions, including school schedules, that contribute to people congregating indoors during winter.
In Georgia, a handful of cases have been confirmed so far among about 900 nationwide. But many others are suspected.
While health officials continue to tally new cases, the exercise of identifying the mere presence of swine flu is becoming moot with the recognition that it’s circulating throughout the U.S. and its severity now is similar to seasonal flu.
So the focus is shifting to what may happen next fall.
“We’re worrying appropriately,” said Dr. Patrick O’Neal, director of preparedness for the Georgia Division of Public Health. By fall, O’Neal said he hopes that a swine flu vaccine will have been developed.
Based on initial reports of severe cases in Mexico, there were some early fears that this swine flu may be more virulent than the seasonal flu strains that circulate every year. But after examining a wider range of cases and studying the genetics of the virus, CDC officials said it appears similar to seasonal flu in the range of illness it causes.
Experts note that during the first wave of the infamous 1918 pandemic flu in March of that year, it appeared mild — then became highly fatal the next fall.
Even if the swine flu grows no more dangerous than seasonal flu, it still has the likelihood of causing serious disease. Every year, the CDC estimates, 5 percent to 20 percent of the U.S. population catches seasonal flu. More than 200,000 people are hospitalized and 36,000 die annually from flu-related complications.
Data from swine flu’s spread in the Southern Hemisphere is of significant interest to Georgia Tech researchers Pinar Keskinocak and Julie Swann. Last year they were part of a team that developed a sophisticated computer model to help predict how pandemic flu would spread in Georgia, giving local emergency officials ways of estimating resource needs.
The current model is based on a devastating 1918-like virus and shows the disease spreading rapidly in metro Atlanta’s densely populated counties. As data become available about how easily the new swine flu is spread, how often it causes severe disease and what age groups are most affected, health officials will be plugging those numbers into the model to examine when cases may peak and how the spread would be affected by interventions such as school closings and home isolation.
So far the new flu doesn’t appear anything like the model’s worst-case scenario.
“I do want to emphasize there is a real threat,” Swann said. “Based on experience, we do think the big ones hit every 30 years.”
The late spring arrival of swine flu is giving officials time to dust off pandemic plans developed years ago amid fears about the H5N1 avian flu virus, which still hasn’t developed the ability to spread easily between humans.
“It’s a significant wake-up call that it can happen,” said Marilyn Self, disaster readiness manager at the Metropolitan Atlanta Chapter of the American Red Cross.
Copyright 2009 The Atlanta Journal-Constitution