Public discussion of “herd immunity” often treats it like an on-off switch: When the U.S. reaches herd immunity, the crisis will be over; until then, the country has little immunity from Covid-19.
But that’s not right.
Herd immunity is more like a light dimmer. The more people develop immunity — either from having been infected or from being vaccinated — the less easily the virus will spread.
Nearly 30 percent of Americans have now had the virus, according to Youyang Gu, a data scientist. (That includes many people who have never taken a Covid test.) About 18 percent have received at least one vaccine shot. There is some overlap between these two groups, which means that about 40 percent of Americans now have some protection from Covid.
Had these people been exposed to the virus a year ago, they could have become infected — and then spread Covid to others. Today, many are protected.
Caitlin Rivers, an epidemiologist at Johns Hopkins University, wrote in The Washington Post. “After millions of infections and the start of a vaccination campaign, the virus is finally, slowly, starting to run out of new people to infect.”
The pandemic is still a long way from over. And the situation may worsen again, because of a combination of risky behavior and new virus variants. Experts are particularly worried about some states’ rush to lift mask mandates and restrictions on indoor gatherings. For now, however, the virus trends are improving, thanks largely to the rising level of immunity.
When I last gave you an overview of the U.S. situation — two weeks ago — I highlighted a mix of positive trends (declining nursing home deaths and encouraging vaccine news) and negative ones (rising caseloads and falling vaccination numbers). Since then, the good news has largely continued, and the bad news has not. Below is a new update, with help from three charts.
Cases are falling — slowly
When the number of new cases began rising last month, it was reasonable to wonder if the more contagious virus variants were on the verge of sparking a nationwide surge. They have not. In retrospect, the February increase looks like a blip:
three million doses a day, from Johnson & Johnson, Moderna and Pfizer. At that point, three million daily shots will be a more sensible goal.
How quickly the Biden administration and state governments can get there will help determine how many lives are saved and how quickly normal life returns.
The variants look a little less scary
I recommend you keep two different ideas about the variants in mind at the same time: First, one or more of the variants could create terrible problems — by being highly contagious, by reinfecting people who already had Covid or by causing even more severe symptoms. A British study released yesterday, for instance, found that the B.1.1.7 variant increases the risk of death in unvaccinated people.
But — here’s the second idea — the overall evidence on the variants has been more encouraging so far than many people expected. The vaccines are virtually eliminating hospitalizations and death in people who contract a variant. Reinfection does not seem to be widespread. And even if the variants are more contagious, they have not caused the kind of surges that seemed possible a couple of weeks ago.
In Florida, where B.1.1.7 has spread widely, “there’s no sign of any increase in cases,” Dr. Eric Topol of Scripps Research wrote. In South Africa, where the B.1.351 variant was first detected, cases are nonetheless plunging: