May 29 (HealthDay News) -- A vaccine for the H1N1 swine flu virus could be ready in October, if research and testing proceed on pace this summer, a leading U.S. health official said Thursday.
Candidate viruses have been shipped to vaccine manufacturers. But federal officials will have to monitor the safety and effectiveness of any vaccines produced, before full-scale production could begin, Dr. Anne Schuchat, the U.S. Centers for Disease Control and Prevention's interim deputy director for science and public health program, said during an afternoon press conference.
"If everything went really well it would not be until the fall before a vaccine would become available. We are saying at this point not before October," Schuchat said.
It's still not clear whether a swine flu vaccine is needed, Schuchat said. Any decision to move forward would be based on several factors, including the severity and spread of the virus and whether there's a safe and effective vaccine, she said.
So far, infections with the H1N1 swine flu virus continue to be mild and recovery is fairly quick, as is the case with seasonal flu, officials said. On Thursday, the CDC was reporting a total of 8,585 cases in 48 states, including 12 deaths. Testing has found that the virus remains susceptible to two common antiviral drugs, Tamiflu and Relenza, according to the CDC.
Schuchat said the newly identified H1N1 virus continues to behave much like seasonal H1N1 viruses, which may partly explain why this flu strain affects more younger people. "Seasonal H1N1 often causes more disease in younger people, compared with the other strains that can be more common in older people," she said.
Also, when seasonal H1N1 flu strains dominate there are fewer deaths than when H3N2 flu strains dominate, Schuchat said.
"There will be decisions later in the summer or early fall about whether to actually finish the vaccine and how large-scale the production might be, and whether or not an immunization program is going to be recommended for some or much of the population," she said.
Some older people may have partial immunity to the H1N1 swine flu virus because of possible exposure to another H1N1 flu strain circulated prior to 1957. So far, 64 percent of cases of swine flu infection in the United States have been among people aged 5 to 24, while only 1 percent involves people over 65, officials said last week.
One major difference in the new H1N1 strain is that it is spreading just at the time when the seasonal flu season is ending, Schuchat said. "This virus is circulating much later than annual flu viruses. We are really not seeing much of any seasonal flu viruses any more, but we're continuing to see this strain circulate, even though we are almost at June," she said.
During the next few months, scientists will be looking to see if the swine flu virus mutates or becomes resistant to antiviral medications, or is more easily spread among people, she said. The flu season is winding down in the Northern Hemisphere but is just beginning in the Southern Hemisphere.
Schuchat said there's no way to tell now if the H1N1 virus will be more virulent when -- and if -- it returns to the Northern Hemisphere with the approach of winter. "Whether it will dominate among the seasonal flu viruses or whether it will disappear is not predictable right now," she said Tuesday.
The World Health Organization said Thursday that 48 countries have reported 13,398 cases of infection, including 95 deaths, most of them in Mexico, where the outbreak began.
SOURCES: May 28, 2009, teleconference with Anne Schuchat, M.D., interim deputy director for science and public health program, U.S. Centers for Disease Control and Prevention