For many, it's like emerging suddenly from a long, dark tunnel.
Some people who've been laid low for months by so-called "long haul" symptoms after a coronavirus infection say that within days of getting their COVID-19 vaccine, those symptoms nearly disappeared.
Speaking withThe New York Times, Bridget Hayward, a 51-year-old operating room nurse in Alexandria, Va., said that for nearly a year after first becoming infected with SARS-CoV-2, she's had a slew of devastating symptoms. They've included persistent body aches, fatigue, a feeling of being hot even in cool weather, and a "brain fog" that rendered remembering even simple words difficult.
"It was horrifying," she told the newspaper. "It was awful thinking it may never get better, like 'Is this my new normal, am I now damaged this way?'"
But then, just one day after her first dose of the Pfizer COVID-19 vaccine, everything changed.
"It was like, click, everything is fine," she said. Her body temperature has normalized and "it felt like a darkness lifted."
Anecdotal cases like this are popping up around the United States, elating patients and puzzling most experts.
Because long COVID is still a mysterious ailment to begin with, figuring out why vaccination is helping at least some patients recover is a black box of sorts, too.
One study out of Britain -- not yet peer-reviewed -- tracked the health of a group of patients who'd been released from the hospital after a bout of severe COVID-19. According to the Times, the study found that those who'd been vaccinated appeared to have more improvement in symptoms of long COVID versus those who hadn't gotten the shot.
The improvements weren't uniform, however: Among the 44 patients who were vaccinated, 23% saw improvements in issues like joint pain and breathing, but 5.6% saw a worsening of symptoms post-vaccination.
It didn't seem to matter whether the patient got the Pfizer-BioNTech vaccine or the Oxford-AstraZeneca shot.
Indeed, 55-year-old Jim Golen, of Saginaw, Minn., told the Times that his long COVID symptoms actually worsened after his two doses of the Pfizer vaccine. For months after becoming infected with the new coronavirus, he experienced symptoms such as chest pain, brain fog, insomnia and shortness of breath.
Golen said he was finally getting a bit better when, after the second dose of the vaccine, his chest pain and weakness returned even stronger than before. Still, he stressed that he's glad to have gotten the vaccine, because getting a real case of COVID-19 was much worse.
Cases of long COVID patients feeling better after getting a vaccine do appear to far outnumber those of people who got worse.
Speaking with WebMD, 33-year-old Aaron Goyang of Austin, Texas, said that eight or nine months after coming down with COVID-19, his breathing became so labored it would sometimes send him to the emergency room.
However, a few weeks after receiving the Pfizer shots, he's now able to run a mile with no problem.
"I was very thankful for that," he told WebMD.
Dr. Daniel Griffin is an infectious disease specialist at Columbia University in New York City. Speaking with WebMD, he said that long COVID appears to affect about one-fifth of the patients he's treated. But he estimated that since the advent of vaccines, about 30% of long COVID patients get better soon after receiving their shots.
"I'm seeing this chunk of people, they tell me their brain fog has improved, their fatigue is gone, the fevers that wouldn't resolve have now gone," he said. "I'm seeing that personally, and I'm hearing it from my colleagues."
So what's going on?
"It's very hard to say anything definitive about these anecdotal reports of COVID long haulers getting improvement of their symptoms post-vaccination," cautioned Dr. Amesh Adalja, an infectious disease specialist and senior scholar at the Johns Hopkins Center for Health Security, in Baltimore.
"First, we need to understand exactly what the COVID long hauler is: There are no strict diagnostic criteria and not everyone with post-infection symptoms is the same," he said.
"Second, in order to determine whether or not the vaccine is actually having a beneficial impact you have to do a prospective study that is well-designed to remove any chance of a placebo effect being responsible for the symptomatic improvement," Adalja added.
In the meantime, some experts theorize that remnant amounts of SARS-CoV-2 may linger in the body after the initial bout of illness has passed.
"We do know that lingering fragments of dead virus and RNA that remain long after the infection is cleared may stimulate or 'rev up' the immune system," explained Dr. Robert Glatter, an emergency physician at New York City's Lenox Hill Hospital.
"It's possible that COVID-19 vaccination may help to 'reset' or correct this state of immune over-activation," said Glatter, who's helped treat many COVID patients. "It may do this by driving the production of antibodies and T cells, which can help to clear lingering fragments of RNA or dead viral particles."
Speaking with the Times, Dr. Eric Topol, a professor of molecular medicine at the Scripps Research Institute in San Diego, put forth a similar theory.
It's possible that "you have your immune system revved up when you're fighting a reservoir" of virus or RNA remnants, Topol said.
He's currently begun a study to investigate the body's responses -- heart rate, immune system activity, temperature -- before and after a COVID-19 vaccine is delivered.
For Griffin's part, he said only research will help unravel this latest COVID-19 mystery.
In the meantime, "the vaccines are a much-needed bit of hope for the long haul COVID-19 community [and at least] they'll be protected from another SARS-CoV-2 infection."
There's more on long COVID at the U.S. Centers for Disease Control and Prevention.
SOURCES: Robert Glatter, emergency physician, Lenox Hill Hospital, New York City; Amesh A. Adalja, MD, senior scholar, Johns Hopkins Center for Health Security, Baltimore; The New York Times; WebMD