ATLANTA , Georgia -LRB- CNN -RRB- -- Children with high-risk medical conditions or disabilities should be among the first to be vaccinated against H1N1 influenza , also known as swine flu , the Centers for Disease Control and Prevention advised Thursday . CDC : The H1N1 virus is spreading in the United States , particularly in the Southeast . And high-risk children under 18 years of age should be rushed to a doctor at the first sign of the virus , said Dr. Thomas Frieden , CDC director . In addition , doctors should be aware that some otherwise healthy children with bacterial infections may be more susceptible to the flu , he told reporters during a conference call . Frieden said the vaccine should be available by mid-October , and will be free at public hospitals and other sites . All schoolchildren should be vaccinated , he said . `` We also are recommending that all people with underlying conditions get vaccinated -- people who have asthma , diabetes , lung disease , heart disease , neuromuscular conditions , neurological conditions that increase their risk factors and women who are pregnant , '' Frieden added . As of August 22 , there had been 556 deaths in the United States associated with the H1N1 virus , and 42 of those deaths were children under the age of 18 . The figures were published August 28 on the CDC Web site . Thursday , the CDC 's Morbidity and Mortality Weekly Report focused on the pediatric cases -- 36 that were counted among the 477 flu-related deaths up to August 8 . Watch more on what the CDC had to say about H1N1 influenza '' Seven of the children who died were younger than 5 years old , the report said , and 24 had underlying disabilities , such as muscular dystrophy or cerebral palsy , or one or more high-risk medical conditions . Frieden said the H1N1 virus -- which he said never really went away , judging by the cases reported this summer -- is spreading in the United States , particularly in the Southeast . `` The good news is that so far , everything that we 've seen , both in this country and abroad , shows that the virus has not changed to become more deadly . That means that although it may affect lots of people , most people will not be severely ill , '' he said . He noted , however , that both H1N1 and the seasonal flu are unpredictable . Because of this , health professionals have to be ready to change their protocols based on any new information . On Wednesday , the CDC said there were six suspected cases among its approximately 7,000 employees at the Atlanta , Georgia , headquarters . Frieden referenced findings by federal agencies who were asked to study the impact of H1N1 in the Southern Hemisphere . They examined data from Argentina , Australia , Chile , New Zealand and Uruguay , since they more closely resemble U.S. demographics and economic development . `` All countries report that after mid-July , disease activity in most parts of the country decreased . This indicates that the duration of the current influenza season in the Southern Hemisphere , in which the 2009 H1N1 virus is the predominate strain , may be similar in length to an average seasonal influenza season , '' according to the Flu.gov Web site . Earlier Thursday , the Institute of Medicine released a report recommending a major step up in protection for health workers dealing with patients suspected or confirmed to have H1N1 influenza . The institute , in recommendations requested by the CDC , said loose paper masks are inadequate because workers can still breathe in the virus . Instead , health workers should switch to a specific type of mask -- N95 respirators -- that form an airtight seal around the nose and mouth . CNN 's Mariam Falco contributed to this report .