The test results that hot day in early August shouldn’t have surprised me — all the symptoms were there. A few days earlier, fatigue had enveloped me like a weighted blanket. I chalked it up to my weekend of travel. Next, a headache clamped down on the back of my skull. Then my eyeballs started to ache. And soon enough, everything tasted like nothing.

As a reporter who’s covered the coronavirus since the first confirmed U.S. case landed in Seattle, where I live, I should have known what was coming, but there was some part of me that couldn’t quite believe it. I had a breakthrough case of COVID-19 — despite my two shots of the Pfizer-BioNTech vaccine, the second one in April.

I was just one more example of our country’s tug and pull between fantasies of a post-COVID summer and the realities of our still-raging pandemic, in which even the vaccinated can get sick.

Not only was I sick, but I’d exposed my 67-year-old father and extended family during my first trip back to the East Coast since the start of the pandemic. It was just the scenario I had tried to avoid for a year and a half.

Where did I get it? Who knows. Like so many Americans, I had loosened up on wearing masks all the time and physical distancing after getting fully vaccinated. We had flown across the country, seen friends, stayed at a hotel, eaten indoors and, yes, even gone to a long-delayed wedding with other vaccinated people.

I ended up in quarantine at my father’s house. Two rapid antigen tests (taken a day apart) came back negative, but I could tell I was starting to feel sick. After my second negative test, the nurse leveled with me. “Don’t hang your hat on this,” she said of the results. Sure enough, a few days later the results of a PCR test for the coronavirus (this one sent to a lab) confirmed what had become obvious by then.

It was a miserable five days. My legs and arms ached, my fever crept up to 103 and every few hours of sleep would leave my sheets drenched in sweat. I’d drop into bed exhausted after a quick trip to the kitchen. To sum it up, I’d put my breakthrough case of COVID right up there with my worst bouts of flu. Even after my fever broke, I spent the next few weeks feeling low.

Of course, I am very lucky. I didn’t go up against the virus with a naive immune system, like millions of Americans did before vaccines were widely available. And, in much of the world, vaccines are still a distant promise.

“You probably would have gotten much sicker if you had not been vaccinated,” Dr. Francesca Torriani, an infectious-disease physician at the University of California-San Diego, explained to me recently.

As I shuffled around my room checking my fever, it was also reassuring to know that my chances of ending up in the hospital were slim, even with the delta variant. And now, about a month later, I’ve made a full recovery.

The reality is breakthrough cases are becoming more common. Here’s what I wish I’d known when those first symptoms laid me low.

1. Is it time for a reality check about what the vaccines can — and can’t do?

The vaccines aren’t a force field that wards off all things COVID. They were given the green light because they greatly lower your chance of getting seriously ill or dying.

But it was easy for me — and I’m not the only one — to grab onto the idea that, after so many months of trying not to get COVID, the vaccine was, more or less, the finish line. And that made getting sick from the virus unnerving.

After all, there were reassuring findings earlier this year that the vaccine was remarkably good at stopping any infection, even mild ones.

“There was so much initial euphoria about how well these vaccines work,” said Dr. Jeff Duchin, an infectious-disease physician and the public health officer for Seattle and King County. “I think we — in the public health community, in the medical community — facilitated the impression that these vaccines are bulletproof.”

It’s hard to keep adjusting your risk calculations. So if you’d hoped to avoid getting sick at all, even slightly, it may be time for a “reset,” Duchin said. This isn’t to be alarmist but a reminder to clear away expectations that covid is out of your life, and stay vigilant about commonsense precautions.

2. How high are my chances of getting a breakthrough case these days?

It used to be quite rare, but the rise of delta has changed the odds.

“It’s a totally different ballgame with this delta phase,” said Dr. Eric Topol, a professor of molecular medicine and director of the Scripps Research Translational Institute in San Diego. “I think the chance of having a symptomatic infection has gone up substantially.”

But “quantifying that in the U.S. is very challenging” because our “data is so shoddy,” he said.

The vaccinated still have a considerably lower chance of getting infected than those who aren’t protected that way. Los Angeles County collected data over the summer as the delta variant started to surge: Unvaccinated people were five times as likely to test positive than those who were vaccinated.

3. How careful do I need to be if I want to avoid a breakthrough?

Looking back, I wish I’d taken more precautions.

And my advice to friends and family now is: Wear masks, stay away from big gatherings with unvaccinated people and cut down on travel, at least until things calm down.

The U.S. is averaging more than 150,000 coronavirus infections a day (about twice what it was when I fell sick), hospitals are overwhelmed, and the White House has proposed booster shots. Scientists are still making sense of what’s happening with breakthrough cases.

In many parts of the U.S., we’re all more likely to run into the virus than we were in the spring. “Your risk is going to be different if you are in a place that’s very highly vaccinated, with very low level of community spread,” said Dr. Preeti Malani, a specialist in infectious diseases at the University of Michigan. “The piece that’s important is what’s happening in your community.”

4. What does a “mild” case of COVID feel like?

In my case, it was worse than I expected, but in the parlance of public health, it was “mild,” meaning I didn’t end up in the hospital or require oxygen.

This mild category is essentially a catchall, said Dr. Robert Wachter, who chairs the Department of Medicine at the University of California-San Francisco. “Mild” can range from “a day of feeling crummy to being completely laid up in bed for a week, all of your bones hurt and your brain isn’t working well.”

There’s not great data on the details of these mild breakthrough infections, but so far it appears that “you do way better than those who are not vaccinated,” said Dr. Sarang Yoon, an occupational medicine specialist at the University of Utah who was part of a nationwide study by the Centers for Disease Control and Prevention on breakthrough infections.

Yoon’s study, published in June with data collected before the delta surge, found that the presence of fever was cut in half, and the days spent in bed reduced by 60% among people with breakthrough infections, compared with unvaccinated people who got sick.

If you’re vaccinated, the risk of being hospitalized is one-tenth that of the unvaccinated, according to the latest data from the CDC. Those who get severely and critically ill with a breakthrough case tend to be older — in one study done before delta, the median age was 80.5 — with underlying medical conditions such as cardiovascular disease.

5. Can I spread it to others, and do I need to isolate?

Unfortunately, you still have COVID and need to act like it.

Even though my first two tests were negative, I started wearing a mask at my house and keeping my distance from my vaccinated family members. I’m glad I did: No one else got sick.

The delta variant is more than twice as contagious as the original strain of the virus and can build up quickly in your upper respiratory tract, as was shown in a cluster of breakthrough infections linked to Provincetown, Massachusetts, over the summer.

“Even in fully vaccinated, asymptomatic individuals, they can have enough virus to transmit it,” said Dr. Robert Darnell, a physician-scientist at The Rockefeller University.

The science isn’t settled about just how likely vaccinated people are to spread the virus, and it does appear that the amount of virus in the nose decreases faster in people who are vaccinated.

Still, wearing masks and staying isolated from others if you test positive or have symptoms is absolutely critical, Darnell said.

6. Could I get long COVID after a breakthrough infection?

While there’s not a lot of data yet, research does show that breakthrough infections can lead to the kind of persistent symptoms that characterize long COVID, including brain fog, fatigue and headaches. “Hopefully that number is low. Hopefully it doesn’t last as long and it’s not as severe, but it’s just too early to know these things,” Topol said.

Recent research from the United Kingdom, suggests that vaccinated people are about 50% less likely to develop long COVID than those who are unvaccinated.

This story is from a reporting partnership that includes NPR and KHN.

This story was published by Kaiser Health News on September 20, 2021. It is republished with permission.