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Estimating the breadth of Covid immunity in NC

In a two-part series of research briefs, I’ve shown using official state data that North Carolinians with natural immunity are much less likely to contract Covid than even vaccinated individuals (which is in keeping with the large, growing body of research finding that post-infection natural immunity to Covid-19 is stronger than vaccine-induced immunity), and I’ve demonstrated that Covid vaccine mandates do more harm than good.

In that second brief, among other things, I took a look at immunity among adult North Carolinians. They are the ones most affected by vaccine mandates, at risk for losing jobs, participating in society, even traveling or worse. Also, they were the ones whose vaccination levels factored so particularly in the governor’s standard for reopening (at least two-thirds of adults partially vaccinated).

Here are the numbers I used; below I will show how they were derived:

Unlike with people who are vaccinated, there aren’t official records of everyone who has encountered SARS-CoV-2 and fought off a Covid-19 infection. There will be records of those who have tested positive, yes, but as the CDC acknowledges, only about “1 in 4.2 COVID–19 infections were reported.”

Based on that rate of underreporting, how many people in North Carolina must have natural immunity from Covid-19? According to DHHS case numbers and using the CDC multiplier (4.2) to estimate actual infections, divided by the state population, that proportion would be 55.4%. Importantly, it would mean over half of North Carolinians have natural immunity from Covid. Looking at adult North Carolinians, the ones most affected by vaccine mandates, it means that 59.5% have natural immunity. …

Already 70% percent of adults in North Carolina are partially vaccinated, and nearly two-thirds (65%) are fully vaccinated. Meanwhile, well over half of the remaining 30% would have the stronger, more robust natural immunity. So basically we would be worrying about 12.2% of adults.

It shouldn’t need to be said, but those 12.2% of adults without natural or vaccine-based immunity should not worry anyone with natural or vaccine-based immunity.

Adults with natural immunity

As of October 4, from when these figures were originally compiled, there have been 1,187,456 Covid-19 cases in adults. That figure multiplied by the CDC’s 4.2 infections multiplier, minus 16,719 deaths, yields 4,971,136.2 estimated with natural immunity. How does that compare with North Carolina’s adult population? The total estimated population for North Carolina is 10,658,717. Subtracting out the 2,299,691 people in North Carolina ages 0-17 gives the adult population estimate of 8,359,026.

4,971,136.2 estimated with natural immunity is 59.5% of the state’s estimated adult population of 8,359,026.

Adults with vaccine-induced immunity

The state Department of Health and Human Services currently reports that 70% of adult North Carolinians are at least partially vaccinated, which means they have vaccine-induced immunity (and 65% are fully vaccinated).

Adults without either natural or vaccine-induced immunity

If 70% are partially vaccinated, that leaves 30% unvaccinated. Unvaccinated does not mean lacking immunity; a proportion of the unvaccinated will have natural immunity from a prior infection. What is that proportion?

A conservative estimate would be to assume the unvaccinated have the same rate of natural immunity as estimated for the state in general — i.e., that 59.5% of that 30% unvaccinated would have natural immunity. So along with the 70% adults with vaccine-induced immunity we would add 17.85% of adults who are unvaccinated but have natural immunity. With 87.15% of adult North Carolinians with immunity, it would leave only 12.15% of adult North Carolinians estimated to lack either vaccine-induced or natural immunity. Fewer than one in eight.

Jon Sanders / Research Editor and Senior Fellow, Regulatory Studies

Jon Sanders studies regulatory policy, a veritable kudzu of invasive government and unintended consequences. As director of regulatory studies at the John Locke Foundation, Jo...