TUESDAY, Sept. 15, 2009 (HealthDay News) -- The U.S. Food and Drug Administration on Tuesday approved four H1N1 swine flu vaccines, with the first doses expected to be available within four weeks.
"Today's approval is good news for our nation's response to the 2009 H1N1 influenza virus," FDA Commissioner Dr. Margaret A. Hamburg said in a news release. "This vaccine will help protect individuals from serious illness and death from influenza."
The federal government has ordered 195 million doses, but may order more doses if needed, Hamburg said. Typically, 100 million Americans get vaccinated for the regular seasonal flu each year.
An estimated 45 million doses of the vaccines are expected by mid-October. Children and young adults, who seem to be more susceptible to the H1N1 swine flu, as well as pregnant women, health-care workers and people with chronic health conditions such as asthma, diabetes and heart disease, are priority candidates for the vaccine.
Since it first emerged in Mexico and the United States last spring, the H1N1 swine flu has continued to produce relatively mild illness in most people -- much like the seasonal flu -- and recovery is fairly swift.
"The H1N1 vaccines approved today undergo the same rigorous FDA manufacturing oversight, product quality testing and lot release procedures that apply to seasonal influenza vaccines," Dr. Jesse Goodman, the FDA's acting chief scientist, said in the news release.
Preliminary results from clinical trials have shown that just one dose of the H1N1 swine flu shots trigger the desired immune response in most healthy adults eight to 10 days after inoculation, the same as the seasonal influenza vaccine. Health officials had been concerned that two doses of H1N1 swine flu vaccine would be required, greatly diminishing available supplies.
Clinical studies of the H1N1 vaccine are continuing, to determine the optimal dose in children. Those results are expected shortly, the FDA said.
The four vaccines are made by CSL Limited, MedImmune LLC, Novartis Vaccines and Diagnostics Limited, and Sanofi Pasteur Inc. All four firms manufacture the H1N1 vaccines using the same processes, and have a proven safety record producing seasonal influenza vaccines, according to the FDA.
The preliminary trials of the vaccine have shown it to be well-tolerated, with side effects that are similar to those of seasonal flu vaccines. These include soreness at the injection site, as well as possible mild fever, body aches and fatigue for a few days after the inoculation. For the nasal spray vaccine, the most common side effects include runny nose or nasal congestion for all ages, sore throats in adults, and -- in children aged 2 to 6 -- fever, the FDA said.
The FDA stressed that the H1N1 vaccine won't protect against regular seasonal flu. That's why people are urged to get their seasonal flu shots now, even though the H1N1 virus accounts for about 98 percent of the flu circulating right now in the United States.
"We think the novel strain of H1N1 is going to be widely circulating, but as the season progresses we may see other seasonal flu viruses emerge and start to spread. So, it makes sense that people get their seasonal flu shot, because we could very well see those strains of influenza circulate widely as our season progresses," said Tom Skinner, a spokesman for the U.S. Centers for Disease Control and Prevention.
On Monday, several new studies suggested that people infected with swine flu seem to be contagious longer than patients with ordinary seasonal flu are.
But it's not clear what impact the findings will have on health-care experts' recommendations to combat the H1N1 swine flu, since the virus continues to produce relatively mild infections in most people and recovery time is fairly fast, the Associated Press reported.
"This study shows you're not contagious for a day or two" with H1N1 swine flu. "You're probably contagious for about a week," said Gaston De Serres, a scientist at the Institute of Public Health in Quebec, who presented one of the studies Monday at an American Society for Microbiology conference in San Francisco.
Levels of virus present in nasal mucus can give experts an indication of whether the flu can still be spread by coughing and sneezing. In the Canadian study, between 19 percent to 75 percent of people with H1N1 flu still showed signs of virus in their noses eight days after the first onset of symptoms. Two other studies -- one from Singapore, the other from Mexico -- produced similar results.
The meeting is the first major gathering of infectious-disease experts since swine flu emerged last spring in Mexico and the United States, before circulating around much of the globe. The World Health Organization is currently reporting nearly 280,000 cases of infection, with at least 3,205 deaths worldwide.
The CDC has been recommending that people infected with swine flu stay home and avoid contact with others for at least one day after they've been free of fever without the use of fever-reducing medications.
Nancy Cox, director of the CDC's Influenza Division, told the AP that keeping people out of work or school for extended periods of time may not be worth it, since the H1N1 virus continues to cause mostly mild illness, primarily in children and young adults.
"We tried to have our guidance balance out all of these factors," she said. "It's just virtually impossible not to have virus introduced into settings such as schools and universities."
For more on H1N1 swine flu, visit Flu.gov.