You don’t have to look around much to see what’s at stake when Mainers go to the polls in March.

That’s when voters will decide whether to repeal the law that eliminates philosophical and religious exemptions for student vaccinations, the subject of a people’s veto challenge after it was passed in the last legislative session by the slimmest of margins.

Liberal use of those exemptions has left Maine vulnerable to outbreaks of debilitating — and sometimes deadly — infectious diseases that are entirely preventable when enough of the population is vaccinated.

At 5.6 percent, Maine has one of the highest voluntary vaccination opt-out rates for students in the country. That by itself is high enough to undermine herd immunity — the resistance a community has to the spread of infectious disease once a high enough proportion of the population is immune, a state that protects those who legitimately cannot be vaccinated or for whom vaccinations don’t work as well.

But the opt-outs tend to cluster in communities, making things even worse; 43 elementary schools in Maine had 15 percent or higher rates of non-medical opt-outs.

When herd immunity falls, it makes a community vulnerable to a bad outbreak that can spread like wildfire. We’ve already seen signs of sparks all over Maine, with pertussis, or whooping cough, outbreaks at schools in Portland, Falmouth and Saco this year. There was another outbreak this month in Freeport.

Maine had 337 cases of pertussis through October after 446 in 2018, a rate of 33.16 per 1,000 people — more than eight times the national average, and the highest in the nation.

In May, the state also recorded its first case of measles in two years, part of a nationwide outbreak. The student had been vaccinated, which thankfully lessened the symptoms.

Maine’s outbreaks have so far been contained. Not everyone is so lucky.

In 2010, a pertussis outbreak in California fueled by low vaccination rates sickened more than 9,000 people and killed 10 infants.

Similarly, a measles outbreak ongoing on the Pacific island of Samoa, where anti-vaccine activists had helped lower first-year vaccination rates to 31 percent in 2018, has made nearly 4,900 ill and killed 71, mostly children under 5, out of a population of about 200,000.

The elderly and infants are particularly vulnerable to infectious disease, as are people who for medical reasons cannot be vaccinated, as well as the small percentage of the population who do not develop antibodies from vaccinations.

That leaves any community with little to no room for those who don’t vaccinate their children because, for whatever reason, they don’t want to. When too many parents opt out, as has become the case in Maine, it leaves the people who actually have no choice — because they can’t medically be vaccinated or because they have compromised immune systems — unable to freely move about for fear of catching something.

And it leaves entire communities vulnerable to outbreaks.

That’s what’s at stake when Maine votes in March.

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