By David Leonhardt

Good morning. Is the Delta variant more severe than earlier versions of the virus? We look at the latest data.

A big Delta unknown

It remains perhaps the most important unanswered question about the Delta variant: Does it cause more severe illness than earlier versions of the Covid virus — or equally severe symptoms in the average infected person (while clearly being more contagious)?

The question is especially relevant to children and to vaccinated adults. In both groups, earlier versions of Covid were usually manageable. For the vast majority of people, the virus resembled a typical flu, rarely causing serious illness.

If Delta weren't any more severe, it would mean that this encouraging situation had not changed. On the other hand, if Delta were substantially more severe, it could call for a much more cautious approach to everyday life.

So what's the answer?

We still can't be sure, and future data could change the picture. But the evidence so far suggests that Delta is similarly severe to earlier versions of the virus, probably with only modest differences in one direction or the other. While Delta is certainly more contagious — and its contagiousness does call for some new precautions, like more frequent mask wearing — its severity does not appear to be fundamentally different. That's a more heartening picture than many people assume.

These tentative conclusions come from three difference sources: expert opinion; research studies; and overall data on cases, hospitalizations and deaths. Let's take them one at a time:

1. Expert opinion

Because the evidence is still emerging and sometimes inconsistent, experts do not read it precisely the same way. Still, I have noticed the broad outlines of a consensus in recent interviews:

• "Any difference is a small difference," Dr. Aaron Richterman of the University of Pennsylvania told me.
• "On a per-infection basis, I don't think it's changed," Jennifer Nuzzo, the lead epidemiologist for the Johns Hopkins Covid-19 Testing Insights Initiative, said. "The risks to vaccinated people haven't really changed."
• "It really is in the 'I don't know stage,'" Dr. Paul Sax of Brigham and Women's Hospital said.
• Dr. Robert Wachter of the University of California, San Francisco, said: "I treat as if it might be a little more severe, but I don't know that it matters that much. I can't think of any public health decision that hinges on whether it's the same or 20 percent worse."
• Dr. David Dowdy of Johns Hopkins pointed out that most people naturally assume Delta is more severe — because it is new, scary and more contagious. Given this bias, he advises assuming it is not more severe absent good evidence. He thinks it's equally likely that Delta is slightly more severe or slightly less severe.

2. The research

The studies evaluating Delta's severity have been frustratingly inconsistent. "There has been mixed evidence about whether it's more severe or not," Dr. Rebecca Wurtz of the University of Minnesota told me. "The final word is not yet in."

Some research — like a study from Scotland — has found that the people who contract Delta get sicker on average than similar people who contracted an earlier version of the virus. Other evidence says otherwise. As Ariana Eunjung Cha of The Washington Post wrote:

A recent technical paper out of Britain suggested the Delta variant does not cause more serious illness than its predecessors, but the analysis did not specifically break out children. David Rubin, a researcher at Children's Hospital of Philadelphia who has been studying U.S. hospitalization data, said that in recent weeks, 1,200 to 1,400 children were inpatients at the peak, and while those numbers may be large, the rate of hospitalization remains the same as in the past at 0.8 to 0.9 percent.

Dowdy notes that the more alarming findings tend to receive more public attention, but that doesn't make them more likely to be right.

3. The topline data

The broad Covid data is probably the biggest reason to doubt that Delta is meaningfully more severe than earlier versions of the virus. The share of Covid cases leading to hospitalization seems to have held steady or even declined in recent months.

That's true in Britain, including among children too young to be vaccinated. It's true among both vaccinated and unvaccinated Americans in places that publish detailed numbers, like the state of Utah and the city of Seattle. And it's true among the full U.S. population: Total cases have risen almost fifteenfold since their June nadir, while hospital admissions have risen about sixfold.

By themselves, none of these comparisons prove much, because the mix of who gets Covid can change over time. But if Delta were significantly more severe, you'd expect to see some signs that hospitalizations or deaths were rising faster than new cases. Those signs are hard to find.

The bottom line

Figuring out how this data should affect your daily life isn't easy, I realize. The situation is uncertain, and different people will make different decisions.

Maybe this frame is helpful: For children and vaccinated adults without other major health problems, there are a lot of reassuring signs. Covid appears to present less risk than some other daily activities. Among Americans under 17, fewer than 500 have died of Covid since the pandemic began; many more — a few thousand every year — die in vehicle crashes.

As Wachter said about Covid this week, "Risk is low enough to live life, high enough to be careful."

For people who do have a health condition that increases their risks — like severe obesity, a previous organ transplant or an active case of cancer — the calculations may be different. Most children hospitalized with Covid, for example, have been older teenagers with a serious pre-existing health condition, Dr. Jennifer Lighter of N.Y.U. told me. Because Delta has caused a surge in Covid cases, it represents a threat to vulnerable people.

The hardest calls may be for vaccinated people who are over 65 and generally healthy. Delta's severity does not appear to be fundamentally different for them, either. But their hospitalization rate has risen more rapidly in recent weeks than that of other groups. I understand why some older people may choose to err on the side of caution until we better understand Delta.

And what about the one-quarter of American adults who have not received a vaccine shot? They continue to have abundant reason to fear Covid.

More on the virus:

• President Biden will present a push for stricter vaccine mandates today.
• Covax, the U.N.-backed program to vaccinate the world, said that it would have 1.4 billion doses available this year, half a billion fewer than it had forecast.
• The Times breaks down pediatric hospitalizations in these charts.

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ARTS AND IDEAS

What's new this N.F.L. season

After the strangest season in league history, the N.F.L. will resume its familiar rhythms tonight — with fans packing stadiums and Tom Brady defending a Super Bowl title — when the Tampa Bay Buccaneers host the Dallas Cowboys.

So much else, though, about how football will look, and be played, in this second pandemic season is different. Here are four things that you should know:

1. The N.F.L. expanded the regular-season schedule to 17 games, from 16. Watch for single-season records to fall, coaches to preserve starters' health by pulling them earlier in blowouts, and the Houston Texans to try and avoid becoming the first team to go 0-17.

2. The N.F.L. played into its image as the No Fun League by vowing to crack down on taunting. That means such heinous acts as spinning the ball or pointing a finger will result in a 15-yard penalty.

3. In a move bound to confuse viewers, many different positions — not just quarterbacks, kickers and punters — can now wear single-digit numbers.

4. For the first time since 2012, at least three rookie quarterbacks are expected to start in Week 1: Trevor Lawrence (Jaguars), Zach Wilson (Jets) and Mac Jones (Patriots). — Ben Shpigel, Times sports reporter

For more: The Times previewed the A.F.C. and the N.F.C.

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Thanks for spending part of your morning with The Times. See you tomorrow. — David

P.S. After Mao Zedong died 45 years ago today, The Times called him "a Chinese patriot, a combative revolutionary, a fervent evangelist, a Marxist theorist, a soldier, a statesman and poet."

Here's today's print front page.

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Claire Moses, Ian Prasad Philbrick, Tom Wright-Piersanti, Ashley Wu and Sanam Yar contributed to The Morning. You can reach the team at themorning@nytimes.com.

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