Is North Carolina already at herd immunity?

By Jon Sanders

Raleigh, NC – Today North Carolina should hit a new threshold in the Covid-19 era: over a million confirmed cases since the pandemic began. But North Carolina may already be at a more important threshold: herd immunity.

photo of people walking on street
Photo by RUN 4 FFWPU

From President Joe Biden all the way down to Gov. Roy Cooper and the “vaccine passports” people, the focus on Covid-19 vaccination has ignored the very important other prong of community immunity: people with natural immunity from Covid.

They are a critical asset to defeating Covid, but (a) their contribution is being completely overlooked, and worse, (b) most of them could potentially be prevented from employment, education, travel, normal commerce, and other things if they don’t submit to a vaccine they don’t need.

Here is what the Centers for Disease Control and Prevention (CDC) has to say about natural immunity. It is on its page on “Immunity Types,” which is a landing page for “Basic and Common Questions” about “Vaccines & Immunizations.”

Active immunity results when exposure to a disease organism triggers the immune system to produce antibodies to that disease. Exposure to the disease organism can occur through infection with the actual disease (resulting in natural immunity), or the introduction of a killed or weakened form of the disease organism through vaccination (vaccine-induced immunity). Either way, if an immune person comes into contact with that disease in the future, their immune system will recognize it and immediately produce the antibodies needed to fight it.

Active immunity is long-lasting, and sometimes life-long.

Lifelong— or at least long-lasting. That isn’t transient immunity. That’s a community shield.

Dr. Marty Makary, professor at the Johns Hopkins School of Medicine, Bloomberg School of Public Health and Carey School of Business, wrote recently in the Wall Street Journal about herd immunity from Covid driven by natural immunity:

… a recent Public Health England study found that less than 1% of 6,614 healthcare workers who had Covid-19 developed a reinfection within five months—even though many of them work with Covid patients. Other experts believe natural immunity is powerful.

“Natural immunity after Covid-19 infection is likely lifelong, extrapolating from data on other coronaviruses that cause severe illness, SARS and MERS,” says Monica Gandhi, an infectious-disease physician and professor at the University of California.

Lifelong immunity truly is lifelong. As the Mayo Clinic page on “Herd Immunity and COVID-19” pointed out as recently as April 14, “those who survived the 1918 flu (influenza) pandemic were later immune to infection with the H1N1 flu, a subtype of influenza A.” For how long was that natural immunity still going strong? The H1N1 flu was during the 2009-10 flu season. That natural immunity was still active over 90 years later.

Nevertheless, obtaining lifelong immunity from a terrible infectious disease is dearly bought if done by contracting and surviving the disease. As explained by the CDC above, vaccines work by replicating natural immunity through the “introduction of a killed or weakened form of the disease organism through vaccination (vaccine-induced immunity).”

The point is, vaccine-induced immunity is to approximate natural immunity. Natural immunity isn’t an afterthought. It’s the gold standard with respect to being immune.

What about community immunity in North Carolina?

The CDC estimates that only about 1 in 4.3 infections of Covid-19 were actually reported (see the May 19 update to its “Estimated Burden of COVID-19” page). As the CDC explains, the reported number of confirmed Covid cases “likely represent only a fraction of the true number of cases that have occurred in the population.” The CDC offers several reasons for such massive undercounting, including especially that asymptomatic infections are likely to go undetected and that some people who are sick and symptomatic would avoid the doctor and not get tested.

With North Carolina reaching a million confirmed cases, assuming North Carolina’s case reporting is similar to the rest of the nation’s with respect to undercounting, how many infections would that mean North Carolina has actually had? A million cases times 4.3 would yield 4.3 million infections. Of those, we know that just over 13,000 have died either with or from Covid. The remaining 4.287 million will have natural immunity.

With respect to community immunity, recall that Gov. Roy Cooper’s standard for removing all of his restrictions on people (including taking face masks off schoolchildren) was two-thirds adults at least partially vaccinated. According to the state Department of Health and Human Services, right now nearly 53% of North Carolina’s adult population are partially vaccinated.

Focusing on the immunity of the adult population, as Cooper did, means discounting the infections of people ages 0–17. Deaths for that age group account for 0% of the state’s Covid deaths.

By estimating the percentage of adult North Carolinians with natural immunity who didn’t also receive a vaccine, then adding that proportion to the percentage of adult North Carolinians at least partially vaccinated, we can estimate how many adult North Carolinians are now immune to Covid.

The estimated proportion of adult North Carolinians with natural immunity is 35%, but some of those would have received vaccinations, too. The estimated proportion of adult North Carolinians with natural immunity alone is 16.5% (see here for how those percentages were derived). Adding the 53% of those adults partially vaccinated to the 16.5% with natural immunity alone would put North Carolina at 69.5% of immunity.

About 70% of adults in North Carolina with active immunity from Covid is obviously past Cooper’s two-thirds standard. More importantly, it would be in line with experts’ estimates of the need for 70% of the population with immunity in order to achieve herd immunity.

In short, North Carolina is very likely at herd immunity from Covid. If not yet, we will be very soon. It is evident by the state’s rapidly falling numbers of new cases and hospitalizations, as well as its Threat-Free Index hitting 99.9%. Community immunity is very good news for North Carolinians.

It also means that there is absolutely no rationale for Cooper to keep North Carolinians under a “State of Emergency,” let alone continue to force children to wear face masks in schools and summer camps.