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Herd immunity threshold in Maine goes up 10% due to COVID-19 delta variant

Maine CDC Director Dr. Nirav Shah said the delta variant is so contagious that more people would need to get the vaccine to prevent outbreaks or case spikes.

AUGUSTA, Maine — Maine's herd immunity threshold for COVID-19 is now at 90% or above due to the infectiousness of the delta variant, according to state public health leaders.

Maine CDC Director Dr. Nirav Shah said in Wednesday's press briefing that because of how quickly and ferociously the delta variant spreads, the pre-delta range of 75-85% of people vaccinated no longer applies.

"Because of the greater infectiousness of the delta variant, much greater infectiousness, the percentage of folks you need to be vaccinated in order to prevent an outbreak or exponential growth has gone from 70% for the pre-delta to over 90% or around 90%," Shah said.

Right now, 74% of those 12 and older have a final dose. That does not account for the 160,017 kids under age 12 who cannot get the shot yet.

Looking at the whole state's population, including those kids, the vaccination rate dips to 65%.

"The closer we can get that number to [90%], the less room the virus has to run," Shah said.

There is another caveat: Shah said herd immunity assumes a "homogenous distribution" of vaccinated people: that is not the case in Maine.

Coastal counties including Cumberland, Lincoln, and Knox have more than 70% of residents vaccinated. Rural counties, especially in western Maine, are under 60%.

"The most disease we have right now in Maine is coming from rural Maine, and that's because we have the lowest vaccination rates there, but those are people who didn't get the first shot to begin with, so we hope they go get the first shot," MaineHealth's chief health improvement officer, Dr. Dora Anne Mills, said during an interview on September 21.

"If folks don't go out and get vaccinated, particularly in the near term, we're going to see pockets, regions of the state, with really high transmission levels," Shah said.

"Now you might say, 'well, hey, that doesn't affect me. I live somewhere else. I don't live in one of those parts of the state where there might be those pockets of transmission.' But you could still be affected," Shah said. "Someone from another part of the state who becomes acutely ill and needs to be transferred to a tertiary care hospital may end up occupying a bed, and it may be your uncle or your neighbor who breaks their hip and has to compete for that same ICU bed, just for that same reason, so the impact of not getting vaccinated reverberates well beyond your own community."

A CDC study found vaccination immunity is stronger than natural immunity: the immune response a person gets from recovering from COVID-19.

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