MILWAUKEE — Over the past year, the scientific world has seen a steady flow of research updating what we know about the novel coronavirus, SARS-CoV-2, and how it affects humans. 

Because the virus is so new, researchers are still grappling with many questions about its function. And because of the nature of the scientific process, no single study can completely answer those questions. Instead, new research is constantly challenging our understanding of the pandemic.

Here, we explore some recent studies that have shed new light on the virus.


Real-world U.S. data show vaccines are effective and may prevent transmission, too

According to an analysis published this week by the Centers for Disease Control and Prevention, the two mRNA vaccines rolling out across the country are both living up to the hype. The shots from Pfizer and Moderna cut the chance of any COVID-19 infection — with or without symptoms — by 90%, the CDC found. 

The study tracked almost 4,000 health care workers and first responders from across the country, all of whom were regularly tested for COVID-19 even if they didn’t show symptoms. 

From December through March, the testing turned up 161 positive cases in unvaccinated workers. There were eight cases among partially vaccinated workers, and just three cases in fully immunized workers (those at least two weeks out from their second shot).

This research adds a couple of pieces to our understanding of the vaccines. First off, it’s a real-world confirmation of the promising results from clinical trials, offering strong protection even to groups whose work puts them at high risk of coronavirus exposure.

“These findings should offer hope to the millions of Americans receiving COVID-19 vaccines each day and to those who will have the opportunity to roll up their sleeves and get vaccinated in the weeks ahead,” CDC Director Rochelle Walensky said in a statement.

The study also found that the Pfizer and Moderna vaccines, which were both designed to include two doses, are very protective after just one shot. Two weeks after the first dose, the vaccines were 80% effective at stopping infections, according to the report — though CDC officials still said getting both shots was important to get the best possible coverage. 

And the report offered clues about a key question for the future of the pandemic: Can vaccinated people pass on the virus to those still waiting for their shots? 

Though not a final answer, the research showed promising signs that the shots may stop COVID-19 transmission as well as sickness. Because the participants were tested regularly, researchers were able to show that the vaccines cut down on asymptomatic cases too, and not just the symptomatic infections that were the focus of earlier clinical trials.

It’s an encouraging sign that the millions of Americans getting their shots each day are protecting their neighbors as well as their own health.

“Our data from the CDC today suggest that vaccinated people do not carry the virus, don’t get sick,” Walensky told MSNBC. “And that it’s not just in the clinical trials, but it’s also in real-world data.” 


Animal hosts may hold the key to the virus’s past — and its future

The World Health Organization released a highly anticipated report on the virus’s origins this week, after sending an international team to China to investigate where the pandemic got its start.

In the report, experts concluded that the most likely pathway was for the virus to pass from bats to humans through another animal host. The coronavirus that’s circulating among humans is genetically pretty different from the closest relative we’ve found in bats, according to the study — so another host species, like pangolins, may have served as an in-between step.

The report said it was “extremely unlikely” that the virus spread from a laboratory accident in China. However, some scientists — including the WHO’s own director-general — have already raised questions about whether the report tells the full story and pushed for further investigation.

In any case, experts are keeping a close eye on any potential animal hosts, because these may be crucial to the future of the coronavirus. If animals are susceptible to the virus, and are able to spread it back to humans, they could throw a wrench in our efforts to get rid of COVID-19 and produce new mutated strains.

Over the past year, scientists have monitored pets, zoo animals, livestock, and even wildlife to see which species may harbor infections. Some creatures — including cows, ducks and chickens — have turned out to be resistant to infection, as Nature reports

But others are more concerning. Ferrets, cats, deer, and some apes have all tested positive for the virus, and mink in particular raised alarms after they were shown to pass the virus back to human handlers.

This has led some zoos to take precautions that look a lot like our human public health measures: Social distancing, mask wearing, and now, even shots in furry arms. Russia registered the first coronavirus vaccine for animals, including dogs, cats, and minks on Wednesday. And some zoo animals, including apes at the San Diego Zoo, have gotten special shots from a veterinary pharmaceutical company.

The COVID-19 pandemic has highlighted the huge potential impacts of a zoonotic disease jumping from animals to humans. And this virus probably won’t be the last to make that leap; in fact, “we can bet on” more of these transmissions in the future, zoonotic disease expert Tony Goldberg told Spectrum News 1.

“The history of medicine is filled with examples of zoonotic diseases,” Goldberg said. “Some of them have come and gone, and some of them have stayed.”


Patients are getting stuck with “long COVID” symptoms even after mild cases

Unraveling the mystery of COVID-19 “long haulers” — those who still struggle with symptoms after the expected period of sickness — remains a pressing issue as millions of patients have survived the disease. 

And rent research has added another layer of complication: It’s not just the sickest patients who face lasting health effects, but also those who had mild symptoms or felt completely fine after testing positive.

"It's very hard to predict who will get these symptoms," Dr. Zijian Chen, the medical director of a post-COVID clinic at Mount Sinai, told CNN.

Research published in February found that months after an initial COVID-19 infection, 30% of patients reported struggling with persistent symptoms — even though the vast majority of them had mild cases and were never hospitalized. Fatigue and loss of smell or taste were the most common problems to stick around.

A March analysis of medical records in California found that, out of hundreds of patients who were struggling with “long COVID” symptoms, almost one-third didn’t have any symptoms in the first 10 days after testing positive. Patients from all different age groups, including children, experienced lasting effects, from insomnia and rapid heart rate to back pain and digestive issues.

And yet another study found that the virus’s long-term effects can include a slew of neurological problems.

At a specialized clinic at Northwestern Memorial Hospital, where the study was conducted, patients have been grappling with emotional or cognitive problems that only developed after their initial, mild COVID-19 cases. Many report issues like brain fog, headaches, numbness, or an altered sense of taste, and perform poorly on cognitive tests, the researchers found. 

“We are seeing people who are really highly, highly functional individuals, used to multitasking all the time and being on top of their game, but, all of a sudden, it’s really a struggle for them,” Dr. Igor J. Koralnik, who oversees the clinic and led the study, told The New York Times.

Experts still aren’t sure what causes symptoms to stick around or even get worse after the initial infection. “Long COVID” may have to do with how the immune system responds to the virus, or with lingering inflammation — but more study is needed to understand the phenomenon, and to support those whose lives are disrupted by it.


Women are reporting more side effects from COVID-19 vaccines

As COVID-19 vaccines have kept rolling out, we’ve learned that some aches and pains are common after a shot — and a small price to pay for strong protection from the virus. But we’ve also learned that not all side effects are created equal. 

In CDC data from the first month of the vaccine rollout, 79% of reported side effects were in women, even though only 61% of doses were given to women. The most common effects included headache, fatigue, and dizziness, the CDC reports.

Women also accounted for almost all of the (still extremely rare) cases of severe allergic reactions to the shots.

For scientists who study the immune system, the disproportionate effects don’t come as a surprise. Women tend to report stronger reactions to other types of vaccines too, from influenza to yellow fever to DPT, infectious disease expert Dr. Larry Schlesinger told Healthline.

“In women, there is an exuberant and stronger response (to many vaccines),” he said. “There’s actually a lot of science behind this.”

The disparity may have to do with hormonal differences: Estrogen has been shown to heighten the immune response, while testosterone dampens it. So, when women feel a stronger reaction to their COVID-19 shots, it’s probably because their bodies are churning out more of the antibodies that will protect them from infection.

Other factors can also lead to stronger side effects, and for similar reasons. Younger adults and people who have recovered from COVID-19 tend to feel more severe effects from their shots, and the second dose of an mRNA vaccine tends to provoke more noticeable reactions. 

Such effects can be a sign that your immune response is kicking in more strongly — whether because of age or a prior exposure to the virus’s spike. 

Of course, experts still stress that the protection from COVID-19 is worth some discomfort after the shot. Those side effects are actually a sign that “you are mounting a very robust immune response, and you will likely be protected as a result,” as Johns Hopkins immunologist Sabra Klein told The New York Times.


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