After another year of living with COVID-19, we have a greater understanding of the respiratory illness than we did nearly three years ago, when the World Health Organization declared a pandemic on March 11, 2020.

In the past year alone, dozens of studies were published in both peer-reviewed journals and as preprints — including on long COVID, the omicron variant, reinfections, the vaccines and more — in an effort to help expand the world’s knowledge of the constantly evolving virus.

To date, more than 100 million people in the U.S. have tested positive for COVID-19 and more than 1 million have died from it, according to Johns Hopkins University. Worldwide, there have been over 657 million confirmed cases of COVID-19 in total.

Now the year comes to an end with nearly 229 million people in the U.S. vaccinated against the virus with two doses, Centers for Disease Control and Prevention data shows. Additionally, more than 45 million of those people have gotten an updated booster dose.

Here is a roundup of our coverage on eight noteworthy studies published in 2022:

COVID booster may lower protection against omicron reinfection, study finds. Here’s why

A COVID-19 booster, specifically a third vaccine dose, may lower protection against getting infected with the omicron variant again for some people — and there’s a reason why, findings suggest.

In contrast, two vaccine doses, followed by an initial omicron infection, may protect more against a second omicron infection than an extra jab, according to a preprint study published Nov. 1 to medRxiv, a server run by Yale, BMJ and Cold Spring Harbor Laboratory. This is due to a specific reaction within the immune system, researchers concluded.

“If you got infected with Omicron at any time, a third vaccine dose actually doubles your risk of reinfection compared to 2 doses only,” Dr. Daniele Focosi, who specializes in hematology and works at Pisa University Hospital in Italy, wrote on Twitter in response to the findings. “Amazing immune imprinting at work.”

The study points to immune imprinting as the reason why “three-dose vaccination was associated with reduced protection compared to that of two-dose vaccination.”

But what exactly is immune imprinting?

Fortune explains it as “a phenomenon in which an initial exposure to a virus — say, the original strain of COVID, by infection or vaccination — limits a person’s future immune response against new variants.”

Authors of the Qatar study wrote how they sought to investigate the “phenomenon” by analyzing COVID-19 data recorded in the country’s national databases during the beginning of the omicron wave on Dec. 19 through Sept 15.

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How soon can you be reinfected with COVID? Quicker than you may think, studies find

Yes, it’s possible to get reinfected with COVID-19 after catching the coronavirus once — and it can happen quicker than you may realize, recent studies have found.

That’s the case even if you’re fully vaccinated.

The record for the quickest recorded COVID-19 reinfection was reported Wednesday, April 20, after a healthcare worker got sick with the virus 20 days after an initial infection, according to researchers in Spain.

The 31-year-old woman, who is fully vaccinated and had received a booster shot, tested positive for the coronavirus omicron variant 20 days after getting sick with the delta variant, a news release from the European Congress of Clinical Microbiology & Infectious Diseases said.

This comes after the Centers for Disease Control and Prevention reported an individual between the age of 12 through 17 was reinfected with omicron 23 days after a previous delta infection, according to a study released April 7. They were unvaccinated.

In the case of the healthcare worker, she had gotten a booster shot 12 days before her initial delta infection on Dec. 20, the news release said. She was asymptomatic during her first bout with the virus.

On Jan. 10, she again started feeling sick — this time coughing and running a fever — so she took a PCR test, which came back positive for COVID-19, according to the Spanish researchers. Genome sequencing confirmed the two separate infections as delta and then omicron.

The news release noted how omicron is much more infectious than delta.

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Will you get long COVID? Study breaks down the odds of recovery months after infection

It’s likely you’ve heard of long COVID by now, and you may be wondering what’s the likelihood of developing it after a COVID-19 infection.

Researchers in Scotland have sought to determine a person’s long COVID chances in a new, nationwide study examining thousands of people in the country who had the virus compared with those who didn’t.

Long COVID, or post-COVID conditions, is when virus symptoms last much longer than expected — preventing some from a full recovery — and scientists are still trying to understand the entire scope of the condition.

The Centers for Disease Control and Prevention defines post-COVID conditions as “new, returning, or ongoing” health issues experienced at least four weeks after a COVID-19 infection. Meanwhile, the World Health Organization defines it as occurring within three months after an infection, with symptoms persisting for two months or longer.

Scottish researchers discovered that 48% of study participants still had COVID-19 symptoms between six and 18 months after a recorded, symptomatic COVID-19 infection, according to the findings published Oct. 12 in the journal Nature Communications. Of the group, 42% reported only partially recovering and 6%, or 1 in 20, reported they had not recovered at all.

The work examined 33,281 people who had a laboratory-confirmed COVID-19 infection, according to the researchers. For comparison, the remaining 62,957 study participants were people never known to be infected. The average age of those studied was 45.

“While most people recover quickly and completely after infection with COVID-19, some people develop a wide variety of long-term problems,” lead researcher and public health professor Jill Pell, of the University of Glasgow, said in a statement.

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COVID-sniffing dogs can also smell long-term virus symptoms in patients, study says

While researchers already discovered a trained dog’s nose can identify COVID-19 with its scent-detecting capabilities, dogs have now demonstrated they can also sniff out long-term virus symptoms — often called “long COVID” — in patients, researchers in Germany found.

Dogs are “superior smellers” and are already used to detect what the human nose typically cannot from diseases, such as Parkinson’s, cancer and diabetes, to drugs and explosives in public places, according to the American Lung Association.

In a pilot study, scientists discovered dogs trained to detect COVID-19 in their prior research could identify long COVID patient samples with a “high sensitivity,” according to the work published June 16 in Frontiers in Medicine.

“These results suggest that the disease-specific odor of acute COVID-19 is still present in the majority of Long COVID samples,” study authors from the University of Veterinary Medicine in Hanover, Germany wrote.

Long COVID symptoms can linger for weeks, or even years, after an infection with “new, returning or ongoing health problems,” according to the Centers for Disease Control and Prevention. They may be identified weeks after first testing positive for the coronavirus and symptoms can include fatigue, breathing troubles, heart palpitations, brain fog and more.

In the study, the team of German researchers had nine dogs dip their noses into scent holes containing samples of long COVID patient saliva as well as COVID-19 positive and negative patient samples of saliva, urine and sweat for comparison during two test scenarios.

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Keep getting COVID? Each time increases the risk of health complications, study finds

For those who catch COVID-19 more than once, each reinfection may increase the risk of health complications, according to a new study published as a preprint.

The increased risks were seen in both unvaccinated and vaccinated individuals, including those who had gotten a booster dose, study authors from the Washington University School of Medicine and VA Saint Louis Health Care System wrote in their research, which is currently under review by Nature Portfolio, published June 17.

The work, titled “Outcomes of SARS-CoV-2 Reinfection,” found that after every COVID-19 reinfection, there was a higher risk of death, hospitalization and lasting health consequences from the virus, including on the lungs and throughout the body, according to the study.

“Risks were lowest in people with 1 infection, increased in people with 2 infections, and highest in people with 3 or more infections,” authors wrote after setting out to address whether reinfections add to “health risks associated” with an initial infection.

Researchers believe the work is the first to fully “characterize” reinfection risks.

In the work, electronic health records from the U.S. Department of Veteran Affairs were examined, including records of 257,427 people infected with COVID-19 for the first time, 38,926 people who were reinfected and 5,396,855 people who were not known to be infected.

Of those reinfected, more than 36,000 had COVID-19 twice, more than 3,000 had been infected three times and more than 200 had been infected four or more times, according to the study.

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Your risk of this debilitating heart condition goes up after getting COVID, study says

People may have a higher chance of developing a debilitating heart condition after COVID-19 infection, a new study published Monday, Dec. 12, found.

The condition, POTS (postural orthostatic tachycardia syndrome), is a nervous system disorder that causes a person’s heart to rapidly race in the 10 minutes after standing up, according to Johns Hopkins Medicine. It is accompanied by symptoms that are known to get worse, including lightheadedness and fainting, and has been considered a potential long COVID condition, research noted.

The study also found that getting vaccinated against the coronavirus is linked to a greater chance of developing POTS but to a “lesser extent,” according to a news release on the work, which involved researchers at Cedars-Sinai Medical Center in Los Angeles.

Still, “risks remain higher after infection than after vaccination,” the study published in the peer-reviewed journal Nature Cardiovascular Research said.

The findings come as the U.S. approaches 100 million confirmed cases of COVID-19 since the start of the pandemic, Centers for Disease Control and Prevention data as of Dec. 14 shows.

Though a person’s chances of developing POTS were found to be higher three months after getting vaccinated, they were more than five times higher after a COVID-19 infection than vaccination, according to the study.

Researchers analyzed 284,592 vaccinated individuals and 12,460 people who had had COVID-19 from 2020 to 2022. Participants were patients of the Cedars-Sinai Health System.

“The main message here is that while we see a potential link between COVID-19 vaccination and POTS, preventing COVID-19 through vaccination is still the best way to reduce your risk of developing POTS,” lead study author Dr. Alan C. Kwan said in a statement.

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Can cannabis prevent COVID? Maybe – but not by smoking it, experts say. What to know

A study that suggests components of cannabis can prevent coronavirus infection has sparked quite a buzz on social media.

And in case you’re wondering, smoking weed won’t protect against the virus, experts say.

Two cannabis sativa plant compounds — CBGA and CBDA — were found to prevent coronavirus and its “emerging variants” from infecting human kidney cells in a laboratory, peer-reviewed study by researchers at Oregon State University.

The compounds did so by binding “to the SARS-CoV-2 spike protein, blocking a critical step in the process the virus uses to infect people,” according to a Jan. 10 university news release about the research.

The work has attracted loads of attention and says that alongside vaccines, “small-molecule therapeutic agents are needed to treat or prevent infections” by coronavirus.

“All this time we’ve been listening to the CDC, we should have been eating CBD,” joked comedian Jimmy Kimmel on TV Jan 12 about the study, mentioning another cannabis compound that’s sometimes legally sold in stores, the New York Times reported.

The more familiar psychoactive cannabis compound — THC — produces a sense of euphoria when smoked or ingested in edibles.

“The first thing to note before everyone goes out tries to prevent COVID-19 infection via pot smoking is that these are in vitro experiment,” Dr. Michael Beazely, an associate professor at University of Waterloo in Ontario, Canada, told McClatchy News.

For more on the study, keep reading here:

Yes, COVID vaccines can alter menstrual cycles, study says. What that really means

Since COVID-19 vaccines were created to guard against the infectious coronavirus, curiosity emerged about its effects on the body — including questions on how it could affect a person’s menstrual cycle.

A new study has sought to address concerns, particularly on social media, about if COVID-19 vaccination leads to “abnormal menstrual cycles.”

Researchers found that yes, vaccines can alter a period cycle — but here’s what that means in-depth.

It was discovered one dose of a COVID-19 vaccine is linked to “a small change in cycle length” as menstruating people who got the shot had slightly longer cycles — meaning their period was a little later than expected in the study published Jan. 5 in Obstetrics & Gynecology. The work received government funding from the National Institutes of Health.

Overall, the slight change was just under a one-day increase in the menstrual cycle length, “a longer time between bleeding,” the NIH said in a news release, and it didn’t affect the actual length of a person’s period, according to the study.

Researchers said small variation wasn’t “clinically significant” while defining a “normal cycle” length as 24-38 days.

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Coronavirus & Vaccines: What You Need To Know

Original COVID shots no longer authorized — but newer ones are, FDA says. What to know

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