The report is published in the Sept. 10 online edition of Science.
For the study, researchers created a model to estimate how fast the H1N1 flu might be transmitted from person-to-person. The model showed that for a vaccination program to effective, 70 percent of children aged 6 months to 18 years would have to be vaccinated first, as well as people in high-risk groups. Those groups include pregnant women and those with chronic illnesses, those with immune system disorders, such as people undergoing chemotherapy, and health-care workers.
Longini noted that it may take two doses of the vaccine, given three weeks apart, to provide full protection. This means that it would take about four to six weeks before the vaccine would create enough antibodies to the virus to protect a person from getting the H1N1 flu, he said.
Since the virus spreads especially fast in schools, vaccinating school children is essential, Longini said. According to the study, a single infected child can be expected to pass the virus on to an average of 2.4 other children at their school.
While other strategies, such as social distancing and antiviral medicines are partially effective in slowing the spread of flu, vaccination is the most effective way of controlling a pandemic influenza outbreak, Longini said.
Vaccination increases immunity throughout the population, which slows the spread of infection, which in turn reduces overall illness, hospitalizations and deaths, the researchers noted.
In predicting how fast the H1N1 flu virus spreads, the researchers first estimated how many people one person with the virus will infect, and came up with a range of between 1.3 to 1.7 people. At a 1.6 infection rate, the pandemic could infect a total of 2.2 billion people worldwide over a year. That's an overall illness rate of 32 percent of the entire pop
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