How to judge the risks is always going to be up to interpretation, but to me, it's pretty clear.

Smallpox is the greatest vaccination success story. Smallpox was one of the deadliest killers of human beings of any kind in world history. Various inoculation strategies were used for several centuries, many of them far, far riskier than modern vaccines, but the threat of catching and dying from smallpox was so great that people judged it worth it. Did smallpox vaccines kill people? Yes. Would some of them never have contracted smallpox? Almost certainly. But in return, the disease was progressively eliminated from different countries and continents until it was completely eradicated in 1980. Far, far more lives were saved by the smallpox vaccine than were harmed by it.

But smallpox is an easy one.

How about influenza? The flu doesn't seem that bad, it certainly is nowhere near as deadly as smallpox. The rate of serious reactions to the flu vaccine is about 1 in 1,000,000. If every person in the United States got the flu vaccine every year, you'd expect about 400 people (rounding up) to have bad outcomes. Let's say they're all fatal (they're not). So you have 400 people a year dying from the flu vaccine. Let's say the flu vaccine is 50% effective, because influenza mutates like crazy and gets around immunity frustratingly well. So we have 400 people each year dying for a 50% effective vaccine. Now how many people die from influenza? In the United States, from 1976 to 2007, the estimated annual number is 23,607. So 50% effective rate cuts that in half (everyone is immunized in this scenario) and 11,803 people don't die from influenza.

But there are more factors than just deaths prevented because a person is already immune to the flu strain. At the lowest end of importance, it's just miserable having the flu. But people also miss school and work and life events because they're sick, and immunization reduces those effects as well. And even if the flu vaccine itself grants immunity to 50% of infections, there's still herd immunity, in which people who are immune won't carry and spread the disease, leading to fewer people being infected. Herd immunity is at its strongest at much higher rates of effectiveness, but any level of vaccination helps break chains of infection.

Ultimately, it's a judgment call. Yes, getting vaccinated will harm some people who would never have contracted the disease in question, but without vaccination, a person is at far greater risk from actually contracting the disease than getting the vaccination. And in the aggregate, far more lives are saved when everyone is vaccinated.

And, ultimately, when a vaccine is highly effective and massively-distributed, it can eradicate a disease from the face of the Earth entirely, as we see with smallpox, at which point we have the best possible outcome: nobody has to get vaccinated anymore because the disease simply isn't there to infect people.

If you ask me, there's no real judgment call here. The argument is dramatically on the side of vaccination for everybody that doesn't have a medical reason they can't be.