New Jersey Gov. Chris Christie thinks parents should be able to choose whether to vaccinate their children. "Parents need to have some measure of choice in things as well," he told reporters Monday.

No, they shouldn't. Parents shouldn't have much matter of choice in vaccinating their children because people like Livia Simon don't have a matter of choice in the issue, either.

Simon is a a six-month-old infant in California. Babies her age don't have strong enough immune systems to handle the flu vaccine. So Livia depends on me and you and everyone around her getting vaccinated.

the point of vaccination isn't to stop you from getting disease. it's to stop spread.

More specifically, she depends on something called herd immunity: a firewall that stops a disease from bouncing from me to you and, eventually, to six-month-old Livia. Herd immunity matters the most for those with compromised immune systems like infants, the elderly, and some auto-immune disease patients (some people who have AIDS, for example, can't get the measles vaccine).

The point of getting vaccinated isn't to keep you from getting the flu (or measles, mumps or whooping cough). It's not, as Christie seems to frame it, a decision about keeping your kids safe from disease. It's to keep you and your kids from spreading all those diseases to people like Livia — people who don't have the option to get vaccinated.

this year, we screwed up

This year, we screwed up. Because some people didn't get vaccinated, more than 80 people caught measles in an outbreak that started at Disneyland. At least six of them are infants who are less than 12 months old.

We nearly screwed it up for Livia, too. As her mother Jennifer told the Washington Post earlier this week, Livia had to spend the last month in quarantine because an unvaccinated child who visited her pediatrician's office may have exposed her to the disease.

This is very risky: approximately 1 to 2 of every 1,000 children infected with measles will die from the disease. Luckily, very few people get infected with measles these days (thanks entirely to the vaccine) but, when it strikes, measles will kill.

"Some parents see it as a personal choice, like homeschooling," Jennifer told the Post. "But when you choose not to vaccinate, you’re putting other children at risk. You’re putting your child above other people’s children."

Wearing a seatbelt is a personal choice. Vaccination isn't.

Each day, we make dozens of decisions that directly relate to our health. We decide to wear a seatbelt on our way to work, or we don't. And sometimes, we choose the riskier path for reasons of convenience or comfort or pleasure. We might not wear a bike helmet or we might have a second drink at happy hour (Or a third. Or a fourth).

These are decisions about the amount of risk that we want to take on as individuals, and we accept the risks of our own decisions.

Deciding whether or not to get vaccinations — or to get our children vaccinations — is not one of those decisions. Vaccination is not a personal decision. It has the potential to affect hundreds, maybe thousands, of other people.

vaccination is a decision that Affects hundreds, maybe thousands of other people

Objections to vaccination among those healthy enough to get immunized (those of us over the age of one, essentially) typically just aren't good enough to justify the risk.

Much of it revolves around the safety of the vaccine. Even in the Amish community in Ohio, it wasn't a religious belief that caused low vaccination rates — and laid the groundwork for a huge outbreak. Instead, it was news of two nearby children suffering complications from the shots that turned the community against vaccination.

So let's clear that fact up here right now: the measles vaccine is, without a doubt, safe. Study after study after study confirms this. The study that suggested the measles vaccine was not safe — and had possible links to autism — was retracted by the academic journal Lancet in 2010. The researcher who published the study, Andrew Wakefield, was stripped of his medical license in Britain.

Not only is the measles vaccine safe, it's also incredibly effective. Ninety-seven percent of people who get two doses of the measles vaccine will not catch the disease (compare that to this year's flu vaccine, which reduces the risk of catching the disease by 23 percent). This means that measles is an entirely preventable illness — if all of us get our vaccines.

Preventing measles outbreaks requires nearly universal vaccination

Yes, in the literal sense, parents ultimately get to decide whether to opt-out of vaccination — and, thankfully, the vast majority of them choose to vaccinate their children.

What gets lost in much of the chatter around the current measles outbreak in California is that the vast majority of people do make the right decision on vaccination. About 92 percent of the American population is immunized against measles, for example. The rate of vaccine exemptions is very low.

But research published in 2009 in the New England Journal of Medicine shows that the rate of non-medical exemptions increased from 0.98 percent to 1.48 percent between 1991 and 2004. Even those tiny upticks in opt-outs matter — especially for measles, which is so infectious that it requires near-universal vaccination to stop its spread. A study in Scientific American published data showing that most states are now below the threshold for herd immunity on measles (those are the states with red bars below).

(These state-level figures often mask huge location variation, which you can read more about here.)

For measles — one of the most infectious diseases known to man — the bar for herd immunity is high. Scientists estimate that about 92 to 94 percent of the population needs to get vaccinated to sufficiently protect vulnerable groups from the disease's spread. Measles is viciously contagious: as my colleague Julia Belluz reported earlier this week, when one Amish missionary brought it back to his community with low vaccination rates, it quickly spread to 382 people and took months to contain.

"There are some fluctuations," Cristina Cassetti, program officer at the National Institute of Allergy and Infectious Diseases, told Wired. "and if vaccination levels dip down a little, you get a situation like Disneyland."

Vaccination is not a personal decision, and doctors know that better than the general public. Last fall, Pew Research Center asked both the general public and members of the American Association for the Advancement of Science — the country's largest trade group for scientists — whether parents should be allowed to decide not to vaccinate their children.

"If vaccination levels dip a little, you get something like disneyland"

Thirty percent of parents thought yes, it should be a parents' decision. Among scientists though, the number was much lower: 13 percent thought parents ought to make the call on vaccination. A much larger majority didn't think it should be a parent's choice.

Your vaccination makes it harder for other people you come in contact with to catch the disease. This isn't only important if you interact with infants, the elderly, or people who have compromised immune systems. It's also important if you interact with anyone else who interacts with infants, the elderly, or people who have compromised immune systems.

The decision not to vaccinate is not about health. We have the facts to prove that's just not right. It is a decision that is, at its root, about selfishness: putting beliefs not supported by science ahead of Livia and 4 million other babies born in the past year. These are real risks, and, in deciding to skip vaccines, you are absolutely making them worse.

WATCH: 'Vaccines do not cause autism, they save lives'

Update: Christie issued a statement after his Monday remarks that said he supports some, not all, vaccines being mandatory.