Are some blue states developing herd immunity?

A provocative possibility to follow up on John’s post earlier. The United States may not reach herd immunity this year since the vaccine-skeptical part of the population is too large. (Whether we’ll reach herd immunity next year, after millions more unvaccinated people are infected and recover, is a separate question.) But what about individual states?

Are we going to end up with a two-track pandemic in this country, where blue states with high rates of vaccination are generally clear of COVID while red states with lower rates continue to experience mild-ish outbreaks?

Public-health professor Ashish Jha is thinking about it. As you read this short thread, dwell on this: When the states are ranked by share of their populations that have received at least one dose of the vaccine, the top 22 states (including D.C.) are blue. Not until you reach South Dakota at number 23, which is barely above the national average, do you encounter a red one.

Is he right? Well, here’s the scoreboard of how cases have been trending over the past two weeks among the top 15 states measured by the share of their population that’s fully vaccinated. (Both shots, not just one.) Note the declines.

Every state there has fully vaccinated 35 percent or more of its people. In 13 out of 15, cases are down. In 10 of those, they’re down by more than 20 percent. In the two states where cases are up, they’re barely up.

Does that prove that vaccinations are pushing them into herd immunity? Well, hold on. If you look at the other 36 states (again, including D.C.) you’ll find that cases have declined in most of them too over the past two weeks. Specifically, 27 states have seen cases fall and 12 have seen them fall by 20 percent or more. Tennessee, which has fully vaccinated just a quarter of its population, saw cases drops 24 percent in the last 14 days. It’s not just inoculation rates that are driving infections downward, in other words. Nicer weather and more outdoor activity is doubtless contributing too.

But it *is* interesting that the top 15 in vaccinations have nearly as many states with 20-percent declines in cases as the bottom 36 do. This is interesting too:

Los Angeles County recorded no new deaths from covid-19 on Sunday, the first time that’s happened since L.A. County identified its first coronavirus death on March 10, 2020. And while experts warn there’s a possibility of undercounting that typically happens on weekends, it’s still a great sign that Southern California and the U.S. more broadly is getting a handle on a health crisis that has plagued the entire world for over a year.

L.A. County is the most populous in the United States with 10 million people. Not a single COVID death yesterday. The positivity rate countywide is just 0.6 percent whereas California’s statewide rate is a mere 0.9. After a sluggish start on vaccinations earlier this year, the state has raced towards the top of the pack with 50 percent having received their first dose, good for 11th out of 50 states. We’re left to wonder: Has California developed a degree of herd immunity already?

In a month, will its curve look like this?

Another noteworthy fact about California is that, at an estimated 11 percent, the share of residents who are hesitant about getting vaccinated is unusually low relative to the U.S. average. Only the indigo blue states of Massachusetts, Vermont, Connecticut, and Hawaii have lower rates. There may be no red states capable of achieving herd immunity (at least not without naturally acquired immunity among a huge chunk of the population) but the most deeply Democratic states really might get there soon due to very high support for vaccination among residents. It seems totally possible that California will have reached 75-80 percent immunized by July 4. If you’re booking a vacation and COVID risk is a consideration, Cali should be hopping.

By the way, the governors of New York, New Jersey, and Connecticut announced today that all three states will be reopening (mostly) on May 19. As you can see from the chart above, they’re all in the top 15 when measured by the share of the population that’s fully vaccinated and all have seen declines in cases of 40 percent or more over the last 14 days. The positivity rate is 2.7 percent in CT today, 1.8 percent in NY, and 0.7 percent in NJ. The tri-state area should also be fun this summer.

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