Lotta groaning about this clip today among the righties I follow on Twitter, for understandable reasons. “They’re just trying to drive us crazy. There’s no other satisfying explanation,” tweeted Noah Rothman after watching.

It’s another mixed message from a medical expert underselling the vaccine. Normally the underselling takes the form of discouraging vaccinated people from getting back to normal. You’re welcome to gather with other vaccinated people in small groups, the CDC tells us, but stay away from restaurants, movie theaters, airlines — anything you enjoyed about your life in the Before Times. In this case, Gupta is underselling it by warning that vaccinations carry their own risk, namely that evolutionary pressure will lead the virus to mutate in vaccine-resistant ways when it infects a vaccinated person. Which means … we’re going to breed a super-coronavirus by getting vaccinated, I guess? We shouldn’t get vaccinated?

That’s not what he’s saying but the messaging here is not the best, let us say. Watch first, then read on.

Here’s CNN’s @drsanjaygupta trying to defend Fauci saying we should wear masks after being vaccinated: “The virus learns how to, sort of, adapt and mutate now to a vaccinated person. Exposing vaccinated people to the virus, you could start to inspire more and more mutations” pic.twitter.com/rDwZUgE2li

— Tom Elliott (@tomselliott) March 18, 2021

He’s definitely not saying that we shouldn’t get vaccinated. Gupta’s participating in a pro-vaccine ad campaign to encourage people to do so, in fact. What makes the clip confusing is that it’s common knowledge by now even among laymen that mass vaccination is supposed to be the way we prevent new variants from arising. Every time the virus infects someone and starts reproducing, particularly someone with a compromised immune system, there’s a chance that it’ll mutate randomly during replication into a form that makes it fitter to survive, whether by becoming more contagious or more resistant to antibodies or what have you. Logically, then, by reducing the virus’s opportunities to replicate, we reduce the chance of a killer new variant forming. Solution: Mass immunization. By priming a given population’s immune systems to crush the virus on first contact, it never gets a chance to evolve. Vaccination, especially on a wide scale, is kryptonite to nascent variants.

So what’s Gupta going on about at the end of the clip, when he talks about the virus mutating in vaccinated people? This NPR interview from last month helps explain. It’s possible for the virus to replicate in a vaccinated person’s system; no vaccine is 100 percent effective, right? In cases where that happens, there’s a chance that the virus will mutate in a way that makes it capable of overcoming even a strong immune response like a vaccinated person might have. Bad! But that doesn’t mean that a killer super-corona will soon be on the loose.

HARRIS: That’s because the virus is always mutating. And if one happens to produce a mutation that makes it less vulnerable to the vaccine, that virus could simply multiply in a vaccinated individual. But even if that happens, that’s only one step in the process…

If the vaccine keeps virus levels low, even mutated viruses, the infected person won’t produce enough to spread to other people. Unfortunately, at the moment, scientists can’t answer the most basic questions about this process. How much does the virus actually replicate inside a person who has been vaccinated with either one dose or two? And how effective is that vaccine at limiting infection enough so that the virus levels stay low and prevent the spread to other people? Andrew Read at Penn State University says, whatever the answers may be, vaccine resistance or escape, as it’s called, isn’t nearly as scary as bacteria becoming resistant to antibiotics…

A vaccine may become less potent. But in other cases where this has happened, it still works.

Just because a virus mutates inside a vaccinated person to become vaccine-resistant doesn’t guarantee there’ll be enough of a viral load for that person to pass it on to someone else. The vaccine may reduce replication of the virus even if it doesn’t prevent it entirely. Not only that, notes NPR, but because we have three different kinds of vaccines on the market, a new variant that resists one vaccine may be vulnerable to one of the others. That’ll also limit its ability to spread widely, assume it spreads from the initial person at all. The point Gupta’s making comes in the context of the Rand Paul/Anthony Fauci debate today over masks: Even vaccinated people should wear masks for awhile, Gupta’s saying, because there’s a chance that one of those vaccine-resistant mutations will happen in their system and, if it does, we want to reduce the chance of them transmitting the virus to someone else as much as possible. Otherwise we’ll end up with an outbreak from a dangerous strain.

Which raises a question: Does that mean even vaccinated people need to wear masks forever?

I don’t think any medical expert would say that. (Although maybe some of them are thinking it? They’re really cautious about risk-taking during the pandemic.) Gupta would presumably say that we should wear masks while we’re in this “in between” period where many people have been vaccinated but many are still unvaccinated and so the virus is still traveling pretty freely. Eventually, God willing, we’ll reach a point where there’s so much immunity across the population that infections just aren’t happening anymore in meaningful numbers. That means few opportunities for the virus to mutate by chance into a vaccine-resistant strain. But right now, when vaccinated people are still routinely encountering infected people in the population and we’re doing 50-60,000 cases per day, Gupta would rather have everyone play it safe by masking up. Even the people who’ve had both shots.