In the united states, what is the main federal agency for the promotion of public health and welfare?

Astudy shows that an influenza vaccine is 71.4% effective in preventing a particular type of influenza. if 15,422 people receive the vaccine, how many would not be protected and would be likely to get infulenza?

If an online school program (i.e k12, ecot) assigns me a computer, would it be ok to use social media on it? would i get in trouble? i am not really sure from reading their terms and such.

[120 total points] (public health) in one of the largest human experiments ever conducted, in 1954 a randomized controlled trial was run to see whether a vaccine developed by a doctor named jonas salk was effective in preventing paralytic polio. a total of 401,974 children (ages 6–9), chosen to be representative of those who might be susceptible to the disease, were randomized to two groups: 200,745 children (the control group c) were injected with a harmless saline solution (a placebo) and the other 201,229 children (the treatment group t) were injected with salk’s vaccine.what was the point of giving saline solution to the children who didn’t get the vaccine? explain briefly.