FRIDAY, July 24, 2009 (HealthDay News) -- The H1N1 swine flu could end up affecting as many as 40 percent of Americans, if one includes workers who stay home to care for people who contract the illness, U.S. health officials said Friday.
The projection from the U.S. Centers for Disease Control and Prevention is based on the influenza pandemic in 1957, when almost 70,000 people in the United States died from the flu.
"Our planning assumptions for a severe pandemic were that up to 40 percent of the workforce might be affected and not able to work, either because they were ill or because they needed to stay home to care for an ill family member," Dr. Anne Schuchat, director of CDC's National Center for Immunization and Respiratory Diseases, said Friday in a press conference.
But even if the new H1N1 virus never reaches that proportion, it is expected to gain strength come fall.
"We had a 6 to 8 percent attack rate just during the spring months," Schuchat said. "We think that in a longer winter season, attack rates would be two to three times as high as that," she said.
A public health campaign and a vaccination program, which will probably begin in October, could reduce the impact of the H1N1 swine flu, she said.
"We think we can limit, somewhat, the illness and severe complications of that kind of virus circulation with updated guidance and, of course, with the efforts we are making towards the development of a vaccine," Schuchat said.
Vaccine trials, already underway in Australia, are expected to begin in the United States next week, Schuchat said.
U.S. officials hope to have 160 million doses of injectable swine flu vaccine on hand by October, with more doses coming in the form of a nasal spray -- if trials of experimental vaccines are successful.
To determine who should receive the vaccine first, the CDC's Advisory Committee on Immunization Practices will meet Wednesday.
In the Southern Hemisphere, where it is winter now, seasonal flu and the new H1N1 swine flu continue to spread, Schuchat said.
The good news is that "specimens we have collected have not changed. They are still the same strain we are seeing here, meaning that the vaccine we are working on is directed against the strain that is still active both here in the U.S. and in Southern Hemisphere countries," she said.
Also, the CDC, in this week's Morbidity and Mortality Weekly Report, cited four children in Texas who developed neurological complications from encephalitis, associated with the H1N1 flu. Two of them also had seizures, but all recovered and had no lasting neurological effects after leaving the hospital.
"This is a reminder that seizure, encephalitis and other neurologic complications can occur in the setting of influenza," she said.
Although less severe in summer, the H1N1 swine flu continues to spread, especially in summer camps and schools, Schuchat said.
Reacting to reports that some camps are giving children the antiviral drug Tamiflu in hopes of preventing the virus, Schuchat advised against this. Camps should follow the CDC's guidelines on protecting campers from the flu, she said.
Giving antiviral medications in hopes of providing a general immunity can increase the odds that the virus will become resistant to the drugs, Schuchat said. To date, five cases of the H1N1 flu have proved resistant to Tamiflu, she noted. So far, this resistant strain has not been passed on to anyone else, she said.
The CDC also reported Friday that there have been 43,771 confirmed cases of H1N1 infection and 302 deaths in the United States, although officials believe more than 1 million Americans have been stricken with swine flu. The reason for the disparity: The virus continues to produce mild symptoms and patients typically recover quickly. This was the final CDC report of case numbers, Schuchat said, noting in the future it will document swine flu trends.
For more information on H1N1 swine flu, visit the U.S. Centers for Disease Control and Prevention.