The first round of H1N1 vaccines—roughly 600,000 doses in total—will be delivered to 25 cities and states Tuesday. Another 6 million to 7 million doses are expected to be available early next week, according to the Centers for Disease Control and Prevention.

The cities and states that will receive the vaccines are the ones who placed the very first orders on Wednesday, CDC officials say. One of those localities is Chicago, where public health officials say healthcare workers and fire department emergency response teams will be the first to take advantage of that city’s 16,000 vaccines. An additional 57,000 doses will be disbursed throughout the surrounding Chicago-land area, according to The Chicago Sun-Times.

The first doses of H1N1 vaccine will be in the form of a nasal spray, which is rated for use only by healthy individuals aged 2-49 years. Vaccines in shot form will likely be available in large quantity and for public consumption in mid-October, according to the CDC. The nasal spray is not recommended for use by either pregnant women or those with chronic conditions—the two groups most at risk for H1N1, according to the Sun-Times.

Meanwhile, a new report from Harvard University shows only 40% of adults are “absolutely certain” they will get the H1N1 shot. Concerns over vaccine side effects, the possibility they will get a serious strain of the virus and uncertainty that medication would be available if they do contract the disease were the top reasons given for not getting the inoculation.