Resolved: Public health concerns justify compulsory immunization....offers some interesting definitional possibilities.
(Unless otherwise noted, definitions from Dictionary.com, which uses the Random House Unabridged Dictionary.)
"Health services to improve and protect community health, esp. sanitation, immunization, and preventive medicine."
Note the largely preventive nature of public health. Immunization is meant to prevent unnecessary sickness, suffering, and death. Note also that the word "public" is important. The agent of action in this resolution is the government, which brings social contract reasoning into play.
"something that relates or pertains to a person; business; affair"
"a matter that engages a person's attention, interest, or care, or that affects a person's welfare or happiness"
This is a particularly prickly word for the affirmative. Although "concern" carries a connotation of anxiety or worry, negatives might argue that the term is vague, and (as a general principle) doesn't rise to the level, say, of an emergency. Affirmatives would do well to combine the above definition of "public health" with the first definition of "concern"--arguing that the very business of "public health" is that of prevention through, among other things, immunization. (Also, they should point out that governments rarely compel trivial immunizations, trying to block out negative arguments about wholesale rights-trampling.
The two major senses of justification may lead to completely different kinds of arguments. Those (especially on the negative) defining the argument in terms of rights will use the first sense: "to show (an act, claim, statement, etc.) to be just or right."
Those advocating a utilitarian approach might use the second definition: "to defend or uphold as warranted or well-grounded." This is much, much broader, and works with a wide array of criteria, including cost-benefit analyses.
The resolution offers no bright line for how immunizations might be compelled: through fines or taxes? Through force? Affirmatives will want to look at the history of compulsory immunization for examples of how governments usually go about it.
Note: a phrase that isn't found in the resolution, but is critical for both sides to understand, is "herd immunity"--the idea that when enough members of a community are resistant to infection, it will effectively disappear in a population, protecting even those members (like conscientious objectors) who refuse to be vaccinated. The threshold is usually above 80%. The aff will argue that, historically, reaching the threshold has required government meddling, if not outright compulsion.