How effective is natural COVID-19 immunity?

COVID-19 Vaccine

DENVER (KDVR) — Natural immunity data isn’t drilled down in Colorado, but it makes the difference between 55% of Coloradans being immune to COVID-19 and 70%.

The Colorado School of Public Health says people who caught COVID-19 have comparable immunity rates to vaccinations.

According to a COVID modeling report released July 28, previous infections of COVID produce between 85% and 92.5% immunity rates depending on whether the infections were symptomatic.

By comparison, people are believed to have anywhere between a 67% to 95% immunity rate after receiving the vaccine, depending on the brand.

In a Thursday press conference, state epidemiologist Dr. Rachel Herlihy said the school of public health’s modeling data alone is not entirely useful for determining actual rates of natural immunity.

“There are some challenges with that data,” said Herlihy. “Typically public surveillance health data is not the best source of data to answer those questions.”

Herlihy said experts would have to track individual cases, exposures and reinfections in order to get Colorado’s true natural immunity rates.

The state, however, does use natural immunity rates in its public statements about Colorado’s overall COVID immunity.

The school of public health uses natural immunity rates in its modeling reports alongside the numbers of daily vaccinations. The state health department uses these reports to tell the public how many Coloradans are COVID immune.

“One in 99 Coloradans are estimated to be currently infected,” reads a health department release,” and 70% of Coloradans are estimated to be immune, by vaccination or by prior infection.”

Remove the natural immunity from that picture and the state is only 55% immune, according to CU Anschutz’s modeling.

KDVR’s Data Desk has asked the health department why natural immunity estimates are suitable for modeling but not for public display and is awaiting a response.

This range of effectiveness syncs natural immunity with vaccine immunity. The length of natural immunity matches the rate of vaccine immunity.

“We assume symptomatic infection confers immunity in 92.5% of people and the percent immune wanes at a rate such that 80% remain immune one year after infection,” reads the report. “We assume asymptomatic infection confers immunity to 85% of people and immunity decays at the same rate as acquired immunity from symptomatic infection.”

A recent Israeli vaccination study said the Pfizer vaccine begin to lose effectiveness after six months – part of the broader federal government’s decision to recommend booster shots to some at-risk groups at least eight months after their date of full vaccination.

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