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(NEXSTAR) – Last year, at the height of our summer surge, the U.S. saw an average 66,784 new COVID-19 cases per day, according to New York Times data.

Over a year later, we have three vaccines on the market, roughly 60% of adults fully vaccinated and summer is looking fairly normal. Oh, except for the fact that we’re seeing more new COVID-19 cases than we were last summer.

On Sunday, the 7-day-average of new cases topped 79,000. The epidemiological curve is still climbing; we haven’t seen the peak yet.

How in the world is that possible? It comes down to three factors, according to the doctors we spoke to.

The summer of ‘wild abandon’

When we reopened, we really, really reopened. Hardly any mask mandates, capacity limits or social distancing.

“In summer of 2020 we were all on high alert,” said Dr. Peter Chin-Hong, infectious disease specialist at University of California, San Francisco. “Even if we wanted to do something, we had to navigate the world carefully because of closures, and things like the reopening tiers in California.”

By mid-June, even strict states like California fully reopened their economies. Birthday parties were back. Weddings resumed. Bars were filled to the brim.

“In summer of 2021, we began the summer with wild abandon. We were fearless. In fact we tried to make up for the past year of missed social activities,” Dr. Chin-Hong said.

Elusive herd immunity

About half of Americans, including children, are fully vaccinated – but that means half are not.

“We reduced the susceptible population by half, which is not a lot,” said Dr. George Rutherford, an epidemiologist at UCSF. “We needed to reduce by 84% for this delta variant.”

Rutherford likened the spread of the virus to a wildfire: “Think of it like forest fire fuel. Just because you’ve gotten rid of half of it, doesn’t mean there’s not plenty around.”

President Joe Biden set a goal: Get at least one dose of the vaccine into 70% of Americans’ arms by July 4. We got there eventually, about a month late. In that time, the delta variant wreaked havoc.

The dreaded delta

The delta variant is probably the factor that sets us most apart from summer 2020 – in a bad way.

“If you went back to February and March (of 2020) and looked at some of the original research from Wuhan, if you were in a household and a case came into the household, about 20% would get infected,” explained Rutherford. “Now, it’s 100%.”

It’s hard to overstate the impact the delta variant has had on the U.S.’s attempt to put COVID in the past.

“Delta is everything right now,” said Chin-Hong. “If it weren’t for delta, we’d be doing pretty well.”

Here’s the good news

While the number of new COVID-19 cases we’re seeing every day is higher than last summer, the number of hospitalizations and deaths are not. Last summer, the U.S. saw more than 1,000 people dying every day for several weeks. Right now, that number is closer to 300.

Why the difference? You guessed it: the vaccines.

New CDC data shows 99.999% of vaccinated Americans have not had a deadly breakthrough case of coronavirus. So while the delta variant is infecting some vaccinated people, very few are ending up with the most dire outcomes.

What’s next?

Back to the bad news real quick: We haven’t actually reached our peak yet. More people are getting infected every day, meaning more people will end up hospitalized and some of them won’t survive. Chin-Hong estimated we may not see the peak until October.

But if there’s a silver lining to this surge, it’s that every additional COVID-19 infection provides some immunity to those who survive. We are inching closer to herd immunity – we’re just doing it the hard way.