Are we closing in on herd immunity?

In January, I wrote a post called “Quit acting like the pandemic is almost over,” in which I shared my general sense that people in the US were starting to act like the pandemic was coming to a close. Bolstered by news of multiple vaccines with high efficacy rates, it was probably natural to start to see the light at the end of the tunnel.

Now that we’re vaccinating millions of people every day, the same sense seems to be building. Texas’ Gov. Abbott says the state is “very close” to herd immunity. Here’s the full quote:

UPDATE 4/16: I forgot to note that the governor of the second largest state, was talking about the state of herd immunity, while admitting that he either didn't understand the concept, or hadn't bothered to learn it, while the pandemic is over a year old. As a sidenote, since 1995, Texas has had George W. Bush, Rick Perry, and Greg Abbott as governor. Might be time for a new direction.

The figures cited by Abbott are solid numbers, but they’re likely not high enough on their own, and it’s only a portion of the picture. Reis Thebault provides the missing bits for Texas:

I’ve seen many estimates of where herd immunity might kick in, and none of them were under 60% (Fauci has it around 80-85%), so Gov. Abbott seems to be getting ahead of himself.

And while Texas does not appear to be anywhere near herd immunity as a whole, its progress is uneven, so some communities are farther than others. Analysis from the Houston Chronicle found that “Texas counties that are poorer, whiter, less-educated and where former President Donald Trump won a larger than average share of the vote have vaccinated a smaller share of their population than the state average.” If that continues, those areas will remain at greater risk of spread.

What is “herd immunity”?

It seems the general public perception of the meaning of the term is that it’s the point where infections essentially stop occurring, but that’s not the case. A Q&A post from the Johns Hopkins School of Public Health shared the following.

Carl Bergstrom is a biologist who has worked to help keep people informed throughout the pandemic. He shared a thread on Twitter recently to help dispel misconceptions around the concept of herd immunity. Do check out the thread, but I’ll give you the short version.

Per Bergstrom, herd immunity isn’t the point where infections stop, but rather where the spread of infection hits its peak. As you can see in the model he shared below, the number of people who have recovered from the disease (represented by the green line) continues to climb long after herd immunity is reached (at the point when the red line peaks).

Once we hit the point where active cases start to decline, we’re in danger of people having the perception that we’re safe and that their lives can return to normal. At this point, there’s an opportunity to stem transition with aggressive controls, something like a brief, intense lockdown period. Prof Bergstrom’s tweet below demonstrates the potential gain—in terms of avoided infections—via such an approach.

A lockdown could save many lives and avoid potential long-term problems for people who would’ve otherwise been infected, and it would also reduce the risk of additional problematic variants. But here’s the problem, how do we sell a meaningful lockdown to a public that’s already sick of the pandemic?

Zeynep Tufecki wrote something related last week, which looks at the recent uptick in cases in the US. Prof Tufecki (like Prof Bergstrom) is a voice I put deep trust in. She’s earned it many times over. (Not many people get NYT headlines like, “How Zeynep Tufekci Keeps Getting the Big Things Right” for their work.) When she says, “We appear to be entering our fourth surge,” and that, “If we act quickly, this surge could be merely a blip for the United States,” we should sit up straight and take notice. But she cautioned that “if we move too slowly, more people will become infected by this terrible new variant, which is acutely dangerous to those who are not yet vaccinated.” That last bit is a call we need to heed.

Vaccines can greatly aid efforts to eliminate the virus, but we need to get them to everyone who’s willing to take them in short order. And not just in the US. It needs to happen globally. Otherwise, we’re offering the virus the opportunity to continue rolling the dice beyond our borders. That’s a dangerous game for all of humanity.

Are we getting there?

While I assume that most of humanity is ready to move on, viruses don’t get bored. They replicate. The WHO reported that global infections were up 9% last week, the seventh week in a row of increases. And while talk of herd immunity is on the rise, no country has even hit the 60% hurdle.

That said, we are seeing benefits from vaccination. Analysis shared last week in the New York Times showed a clear trend in hospital admissions by age groups where older groups that are now more likely to be vaccinated, were less likely to be admitted.

So there’s good news around vaccines, but we need to be patient and remain vigilant. We know the virus won’t let it’s guard down.