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(Tribune News Service) — An estimated 94% of people in the U.S. have been infected with the COVID-19 virus at least once, according to according to a new paper from researchers at Harvard's School of Public Health.

The big reason for the surprising surge? The omicron variant's record-shattering case rates early this year and middling booster rates that fell short of what experts had hoped to see.

While that's far from good news, there is a silver lining: As of early November, the percentage of people with some protection from new infections and severe disease is "substantially higher than in December 2021," according to the authors.

"Moving forward we are in probably the best shape that we've been," said Dr. Peter Chin-Hong, a professor of medicine at the University of California San Francisco who specializes in infectious diseases and did not participate in the study. But that does not mean COVID is less prevalent than before or that you're less likely to catch it. In fact, cases are on the rise again, public health officials warn.

A preprint of the paper, which has not yet been peer-reviewed, was published this week on a website called MedRxiv. The findings contain uncertainties because they are based on a statistical analysis of Centers for Disease Control and Prevention-reported diagnoses, hospitalizations and vaccinations, rather than antibody testing of a representative sample of Americans.

The team estimated that 29.1% of Americans have been vaccinated and infected, 55.7% are vaccinated and reinfected, 2.4% are unvaccinated and infected, 7% are unvaccinated and reinfected. Of those who have never been infected, 3.5% are vaccinated and 2.1% are unvaccinated.

The researchers from Harvard, Yale and Stanford set out to understand how immunity to the virus had changed since December 2021. The calculations studied "the competing influences" of new vaccinations and infections and the waning of immunity earned from them.

They compared the situation as of November 2022 to 11 months before and took into account the fluctuating prevalence of COVID over time and geography, how much and how fast immunity fades, reinfections, vaccination status and the efficacy of those shots.

In December 2021, 59.2% of people had been infected with the COVID-19 virus, they estimated.

"Between Dec. 1, 2021, and Nov. 9, 2022, protection against a new omicron infection rose from 22% to 63% nationally, and protection against an omicron infection leading to severe disease increased from 61% to 89%," the analysis found.

The authors warn that "despite the high level of protection at the beginning of the 2022-2023 winter, risk of reinfection and subsequent severe disease remains present." And they caution that the introduction of "a more transmissible or immune-evading (sub)variant, changes in (human) behavior, or ongoing waning of immunity" could change the calculations.

The study estimated that in less than a year there were 116 million first infections in the country and 209 million reinfections, nearly all from omicron subvariants.

As the virus mutates, our understanding of how population immunity impacts the spread of COVID also evolves.

During each year of the pandemic, the largest surges in California have happened over the winter holidays, but the fact that so many people got COVID earlier this year means fewer might be vulnerable this holiday season, the researchers found. At the beginning of this year the first omicron wave smashed all previous case records, sickening millions but also raising the level of immunity in the population, for at least a while.

Even with high levels of immunity, COVID continues to be a killer virus.

"We still have an unbelievable amount of deaths per day in the U.S.," said Chin-Hong, "even more remarkable given this is a 'lull.' "

California's weekly COVID deaths have stayed under 200 each week so far this month, a far cry from the over 3,779 deaths reported in one week in early January 2021.

It's a huge improvement, but "it's still nothing to celebrate" said Chin-Hong, pointing out that the virus continues to be a leading cause of death in the country. "We could do better."

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