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DENVER (KDVR) — Between vaccines and cases, Colorado could be halfway to herd immunity by Easter.

Herd immunity roughly means the point at which the virus simply has too few carriers to survive as an endemic virus anymore. Individuals can achieve immunity the easy way or the hard way.

“Immunity means your body has an immune system that can recognize and effectively attack this virus,” said Dr. Glen Mays, chair of the Department of Health Systems, Management and Policy at the Colorado School of Public Health. “That recognition can come from exposure to the vaccine or from prior exposure and infection.”

Nobody knows for sure how many people in a given population set need to be immune for herd immunity to kick in, but Mays and others estimate 70%-80%.

Colorado is roughly halfway there between Coloradans who have been infected and those who have received at least on dose of a vaccine. Together, around 2.4 million fall into one or the other of those groups, or 40% of the state’s population.

As of Monday, 1.93 million Coloradans have received a COVID-19 vaccine, or 33% of Colorado’s population.

This does not necessarily mean that 33% is completely immunized, however.

Gov. Jared Polis health team today said about 22% of Colorado is protected against the virus, roughly the amount of those with full vaccination plus those who have been infected.

Except for the Johnson & Johnson vaccine, each of the COVID-19 vaccines in circulation require two shots for maximum efficacy. Only 704,896 Coloradans are “fully immunized,” meaning they’ve either received the Johnson & Johnson vaccine or two doses of one of the others – about 12% of the state’s population.

Another 21% have only received the first but not the second shots, making them partly immunized but not to the extent intended by their respective vaccines.

This puts the ranks of the vaccinated far beyond the number of Coloradans who ever had the virus in the first place.

Only 8% of Coloradans, or 444,390 individuals, have so far contracted COVID-19.

There is not much literature yet exploring how likely the previously infected are to become infected again. Dr. Mays said it is generally true that prior exposure and infection is a form of immunity, but that we do not understand it as well as vaccines.

“To be conservative, at this stage we know a lot more about vaccine-produced immunity than the strength of immunity through prior infection,” said Dr. Mays. “That tips the scales to try to get to herd immunity to the maximum extent possible through vaccination.”

Health department records and the state show the vaccination program ramping up in volume. Throughout March, there are 36,000 vaccines administered daily, on average – over five times the daily number around New Year’s Day.