but if we just preemptively vaccinate then city zero won't be an issue.
The Vaccine for Smallpox is not entirely safe, because the vaccine consists of essentially another virus called Vaccinia.
This is an infectious virus; the Smallpox Vaccine infects the person who has been vaccinated.
Unlike many other Vaccines -- however, there are significant rates of adverse reaction. Further improvements to the vaccine require human testing, and since the disease has been deemed eradicated --- no improvements can really be made:
Average 1 in 1 to 2 million people vaccinated result in deaths, many more people experience severe complications but don't die.
If there are 300 million people vaccinated; then you could estimate that 300 people would die of complications.
It is quite unlikely for you to be one of the 300.......... it's also unlikely for the Smallpox vaccine to help you against Smallpox in the future. Still..... the complications can be pretty nasty, even if you do survive.
Most people should probably deem the extra protection not worth the more immediate very real dangers:
Post-Vaccinial Encephalitis: 1 in ~3 million people vaccinated. 25% of these: permanent neurological damage; 15-25% die.
Vaccinia necrosum: Progressive tissue death ("necrosis") at the original injection site. 1 persion per 1 to 2 million vaccinations; almost always fatal before availability of vaccinia imunoglobins; people with T-Cell deficiencies are particularly at high risk.
Vaccinia Keratitis: accidental transfer of vaccinia virus leading to lesions of the eye. Reaction: threatens eyesight, corneal scarring....
Eczema Vaccinatum. Too horrible to think of; people who already have some form of eczema, atopic dermatitis, or sensitive skin are at high risk and fatalaties have resulted in the past. Virus produces extensive lesions throughout the skin. Patient's life may be saved with early hospitalization and urgent treatment.
1 in 242 million vaccinated will contract a generalized vaccinia infection -- involving pustules forming about the skin distant from the site of injection and generalized rashes throughout the body; for some patients with weakened immune systems, this results in a toxic and potentially fatal course.
1 in 1 million people to be vaccinated on average, develop a systemic reaction to the vaccine which has a likelihood of fatal outcomes; people who have been immunocompromised or have a weak immune system are particularly susceptible.
Even more people have a severe adverse reaction which may be crippling or severe enough to give one pause about if one really needs the vaccine. Is it an appropriate risk tradeoff? What is the true risk of contracting smallpox VS the cost of taking the vaccine?
Successful vaccination always produces a lesion at the vaccination site, within 4 days, and it will leave a permanent mark which may be undesirable; this will be highly itchy, and highly infectious --- easily carried by clothing, and easily transferred to hands or other body parts to come in contact with it. Contact or contact with anything that touched the lesion may result in infection/lesions of vaccinia on other part of the body, and also: contact with other people ("inadvertent vaccination of friends or family, for example").
Weeks of malaise and discomfort after the vaccination are essentially guaranteed; the vaccine will essentially almost definitely make you feel sick, and likely for 3 to 7 days, similar to a cold.
17% to 20% of vaccinees experience a fever exceeding 100 degrees, during the first 2 weeks after vaccination, and plenty of vaccinated experience a fever exceeding 102F for the first 5 days.
Most people vaccinated experience significant irritation at the vaccination site: including significant soreness, and a variety of kinds of skin rashes plus myalgia lasting 5 to 7 days. More rarely: Stevens-Johnson syndrome results, in which necrosis ("tissue death") of the skin results, in a life-threatening condition involving the dermis of the skin separating from the epidermis.