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 vaccine, the second one in April.

It was just one more example of our country's tug and pull between fantasies of a post-COVID-19 summer and the realities of our still-raging pandemic, where even the vaccinated can get sick.

Not only was I sick, but I'd brought the virus home and 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. And it definitely was not the summer vacation I had anticipated.

Where did I get it? Who knows. Like so many Americans, I had loosened up with wearing masks and social distancing after getting fully vaccinated. We had flown across the country, seen friends, stayed at a hotel, eaten indoors and, yes, even went 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 down to the kitchen. To sum it up, I'd put my breakthrough case of COVID-19 right up there with my worst bouts of flu. Even after my fever cleared up, 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 until 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," 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 you should know about getting a breakthrough case — and what I wish I'd known when those first symptoms laid me low:

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

The vaccines aren't a force field that ward off all things COVID-19. They were given the greenlight 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-19, that 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. This was a kind of bonus, we were told. And then in May the Centers for Disease Control and Prevention said go ahead and shed your mask if you're vaccinated.

"There was so much initial euphoria about how well these vaccines work," says 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 dialing up and down your risk calculations. So if you'd hoped to avoid getting sick at all, even slightly, it may be time for a "reset," Duchin says. This isn't to be alarmist but to clear away expectations that COVID-19 is out of your life, and keep up your vigilance about common-sense precautions.

With more people vaccinated, the total number of breakthrough infections will rise, and that's not unexpected, he says. "I don't think our goal should be to achieve zero risk, because that's unrealistic."

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," says Dr. Eric Topol, a professor of molecular medicine at the Scripps Research Translational Institute in La Jolla, Calif. "I think the chance of having a symptomatic infection has gone up substantially."

But he adds, "Quantifying that in the U.S. is very challenging" because our "data is so shoddy."

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

Recent research has tried to pin down how well the vaccines are working against preventing any breakthrough cases during the delta surge, but much of that comes from other countries and estimates vary significantly.

In the U.S., a study published recently in The New England Journal of Medicine concluded that vaccine effectiveness "against any symptomatic disease is considerably lower against the delta variant," dropping from over 90% earlier in the year before delta was the predominant strain to only about 65% in July. Research on breakthrough infections over the summer in New York found the vaccines were still overall about 80% effective against any infection. Each study has its limits.

It's hard to disentangle what's most responsible for the rise in breakthrough infections this summer — whether it's the delta variant itself, waning immunity in some people or that much of the U.S. dropped public health precautions such as masking.

"We don't have good evidence of what's the cause, but we do know all of these things coming together are associated with more breakthroughs," says Rachael Piltch-Loeb, a public health researcher at the Harvard T.H. Chan School of Public Health.

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

Looking back, I wish I'd taken some more precautions.

And my advice is different now when friends and family tell me they want to avoid having a breakthrough case such as mine: Don't leave it all up to the vaccine. Wear masks, stay away from big gatherings with unvaccinated people, cut down on travel, at least until things calm down.

The U.S. is averaging more than 130,000 coronavirus infections a day (about twice what it was when I fell sick), hospitals are being crushed and the White House has proposed booster shots. Scientists are still making sense of what's happening with breakthrough cases.

What's clear is that 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," says Preeti Malani, an infectious disease specialist at the University of Michigan. "The piece that's important is what's happening in your community."

Even with delta, the goal is not to go back to a lockdown mindset though, Malani says. "My hope is that people who are fully vaccinated should really feel like this risk is manageable."

She says, "Feel good about spending time with your friends or having a small dinner party, but make sure everyone is vaccinated."

What does a "mild" case of COVID-19 feel like?

In my case, it was worse than 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, says Dr. Robert Wachter, who chairs the Department of Medicine at the University of California, San Francisco. "Mild" can be "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."

"So even if we call them mild cases, as you've seen, sometimes these are ones you really don't want to have if you can avoid it," he says.

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," says Dr. Sarang Yoon, an occupational medicine specialist at the University of Utah Rocky Mountain Center for Occupational Environmental Health who was part of a nationwide CDC study on breakthrough infections. "In general, in terms of symptom duration, it's much shorter."

Yoon's study, published in June with data collected before the delta surge, offers some reassurance: 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. "These are meaningful decreases," says Matt Thiese, an epidemiologist and colleague of Yoon's who worked on the study. "It can be the difference between having a fever for almost nine days and having a fever for just under three days."

A recent study from the U.K. also shows that if you're sick because of a breakthrough case, it's generally not as bad, and people have fewer symptoms. In fact, the top five symptoms for people with a breakthrough infection were headache, sneezing, runny nose, sore throat and loss of smell. Notably absent: fever and persistent cough, which are in the top five for unvaccinated people, according to the data compiled by the U.K. researchers.

If I get a breakthrough infection, how sick could I get?

Even with delta, the chance of getting a case of COVID-19 that's bad enough to send you to the hospital is still rare.

If you're vaccinated, the risk of being hospitalized is 10 times lower than if you weren't vaccinated, 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 — with underlying medical conditions such as cardiovascular disease.

When I was sick, one thing was in the back of my mind as I monitored my symptoms: Would I have problems catching my breath?

Thankfully, when you get exposed, the vaccine has already set you up with antibodies, a first line of defense, that will neutralize parts of the virus that attach to the mucosal surfaces of your upper respiratory tract, says Torriani at UC San Diego.

"That initial moment when our body is attacked by the virus, that can lead to some disease," she says. It's a bit of a race. The virus may cause you to get a cold, but, in most people, your immune system will "get its act together and thwart that infection from going down into your lungs," Wachter says.

That later stage of COVID-19 also seems to trigger the immune system to get "overly exuberant" and attack your own body, causing severe respiratory problems such as shortness of breath and destructive inflammation. "So if you can prevent that sort of second stage from happening," Wachter says, "you can prevent a lot of the severe illness from COVID." Other parts of your immune system, such as T-cells, are also ready to kick into action if you get sick.

If you're concerned, you can keep an eye on your oxygen levels with a pulse oximeter. That's much more important than your temperature or symptoms, he says.

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

Unfortunately, you still have COVID-19 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 two times 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, Mass., over the summer.

"Even in fully vaccinated, asymptomatic individuals, they can have enough virus to transmit it," says Robert Darnell, a physician scientist at the Rockefeller University. "Delta is very good at replicating, attaching and inserting itself into cells."

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.

Even so, wearing masks and staying isolated from others if you test positive or have symptoms is absolutely critical, Darnell says. He also advises getting tested if you are exposed to someone who has COVID-19, even if you've been vaccinated, "because you could very well get infected or ill, and you want to protect those around you, including all the children who aren't vaccinated."

Could I get long COVID-19 after a breakthrough infection?

The chance I might go on to develop long COVID-19 was front and center in my mind when I had a breakthrough case.

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-19, 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 says.

Recent research from the U.K. suggests that vaccinated people are about 50% less likely to develop long COVID-19 than those who are unvaccinated. The underlying cause of long COVID-19 is still not yet known, so it complicates the picture for researchers even more, but this early evidence offers some reassurance.

"There may be some symptoms like fatigue [that linger], but studies appear to show that vaccination might also decrease the chances of getting long COVID symptoms," Torriani says.

This is not true for everyone, and it's a compelling reason to avoid getting infected altogether, Wachter says. "Some of those mild cases will go on to be long COVID, so you have to factor that in," he says.

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