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Coronavirus Update

Four Years On, the Mysteries of Covid Are Unraveling

(From the New York Times - March 13, 2024)

Why do people’s experiences with Covid vary so widely? And are super dodgers real?

By now, most Americans have had Covid at least once. While the majority of those infected have been hit with flulike symptoms, some have been hospitalized with serious respiratory issues, and others have had no symptoms at all.

Part of this can be explained by the amount of virus we are exposed to, but our bodies also play a big role. People who are older or have existing health problems tend to have more severe symptoms because their immune systems are already weakened. In some cases, the body can fight off the virus before it replicates enough to cause symptoms, or clear it so quickly that a person never tests positive. There’s also strong evidence that vaccination makes illness less severe.

Experts said that most likely, people who have never been infected are fully vaccinated, very cautious about avoiding exposures (through masking and avoiding crowds) or work from home.

Scientists have been trying to investigate if there’s something biologically unique about Covid superdodgers that gives them immunity to infection. But the closest they have come is finding that mutations in the human leukocyte antigen — which signals to the immune system that cells are infected — can help clear out the virus so quickly that a person might be completely asymptomatic.

Does Covid’s spread come down to coughs and sneezes?

In the early days of the pandemic, we all thought Covid was some sort of surface-hopping ninja. We frantically wiped down groceries, washed our hands to the tune of “Happy Birthday” and tried to turn doorknobs with our elbows.

But studies have since showed that contaminated surfaces are rarely to blame for the spread of the virus. It’s more likely to spread through the air we breathe. Some of this may be through large droplets produced when someone coughs or sneezes, which is why public health officials advised early in the pandemic that we stay six feet away from fellow humans.

But research then suggested that the virus could also be carried by aerosols, smaller particles that could infect people from farther away. “These particles kind of behave like cigarette smoke — they come out and float around, and they can drift in the air for a while,” said Linsey Marr, an environmental engineer at Virginia Tech. Dr. Marr and others have found that tiny particles as small as five microns may carry more infectious virus than larger droplets, partly because they are generated from deeper in the lungs.  Other studies have shown that the virus is still evolving to become better at spreading through the air, said Vincent Munster, chief of the virus ecology section at the National Institute of Allergy and Infectious Diseases’ Rocky Mountain Laboratories.

How long do our defenses last?

Generally speaking, an infection or vaccination protects you for several months, said Akiko Iwasaki, a virologist and immunologist at Yale University. But immunity depends on factors such as age, underlying health and whether the virus has picked up mutations that help it evade our defenses.

There are many components of immune protection, including antibodies that circulate in the blood and help detect and neutralize the virus, B cells that make more antibodies as needed and T cells that can learn to recognize and predict variations of the virus spike protein.

Experts believe higher antibody levels are correlated with better protection. But some studies have indicated that antibody levels drop significantly by three months after an infection or a vaccination. And it has been challenging to pinpoint exactly how many antibodies are needed to provide base-line protection, “as new variants are continuously arising,” Dr. Iwasaki said.

T cells provide a different form of protection — reducing the severity of symptoms rather than blocking infection — and research now suggests that this immunity may last a year or longer.

What’s behind the strange symptoms?

While a robust immune response is needed to eliminate the virus, a dysfunctional one may be to blame for many of Covid’s unusual side effects. For example, researchers have found that in people who develop a warped sense of smell or lose it entirely, the virus latches onto ACE2 receptors in cells that support certain nerves in the nose. This sets off a rush of immune cells, which release proteins to clear the infection. In the process, they can inadvertently change the genetic activity of neighboring nerves, disrupting the sense of smell.

Since the nose acts as an entry point to the brain and other parts of the central nervous system, this overly aggressive immune response and subsequent inflammation could also be the key to understanding other lingering neurological effects of Covid, like brain fog, headaches, ringing in the ears, tingling or numbness in the limbs and even depression, said Dr. Maria Elena Ruiz, an infectious-disease specialist at George Washington University.

The painful swelling or discoloration some people develop in their fingers or toes remains more mysterious. But reports of those symptoms have also become less frequent, and it’s possible that past infections or vaccination have made it less likely that people’s immune systems will go haywire, Dr. Ruiz said.

Is there any such thing as a seasonal break from Covid?

When Covid first took off in winter 2020, many people hoped that the summer months (at least in some parts of the world) would bring a reprieve. It’s true that there are naturally more opportunities for aerosol transmission of Covid in the colder months, when people spend more time indoors. Buildings are also more tightly closed in the winter, leading to poorer ventilation and potentially higher levels of pathogens in the air. And some studies suggest that the virus also remains infectious for longer, and particles carrying it are able to stay in the air for a greater period of time, when the relative humidity is low.

But Covid doesn’t seem to be inherently seasonal — “we’ve clearly had surges in the summer as well,” Dr. Marr said.

But experts agreed they would not be surprised if Covid eventually settled into a predictable seasonal pattern, like other respiratory viruses. It’s just difficult to predict if that will take another few years or even decades, Dr. Munster said.

Do children have a secret weapon protecting them against Covid?

Early in the pandemic, people feared that children, as notorious germ spreaders, would catch and spread the virus easily. They also worried that children would fall particularly ill, because they tend to experience some of the most severe outcomes with influenza and R.S.V.

But with Covid, children seem to have largely been spared from severe illness. Only a small number are hospitalized or develop life-threatening conditions like multisystem inflammatory syndrome, or MIS-C.

We now have a clearer idea why that’s the case: Children’s immune systems may be better primed against Covid precisely because they are frequently exposed to the benign coronaviruses that cause common colds, said Dr. Alpana Waghmare, an infectious disease specialist at Seattle Children’s Hospital. Additionally, studies have shown that another defense mechanism, known as the innate immune response, is stronger in children, helping alert their bodies to foreign pathogens such as the virus that causes Covid.

How does the virus wreak havoc on a person for months?

One theory is that, as with other rare side effects, the lingering symptoms or new complications that can occur in the months after an initial infection — known as long Covid — are caused in part by an immune reaction gone awry. People who develop long Covid may have an immune system that responds too aggressively, or not aggressively enough, to acute infection, said Dr. Ziyad Al-Aly, the chief of research and development at the Veterans Affairs St. Louis Healthcare System. Studies have also found that the virus can hide in the body after the main infection is over, provoking a continuous, low-level immune response and inflammation.

Other evidence suggests the virus can damage the lining of blood vessels, causing tiny clots that block circulation to various parts of the body. This may cause lingering achiness in the joints, brain fog, chronic fatigue and dizziness after standing up too suddenly.

Dr. Al-Aly said that while many of Covid’s mysteries have been solved, he fears that the public has grown weary of the virus — when in reality, he said, it’s “not in our rearview mirror yet.”

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As bird flu spreads in the US, is it safe to eat eggs? What to know about the risk to humans

Avian influenza, aka bird flu, has spread to dairy cows in multiple states and one person in Texas. What to know about transmission, symptoms, and food risks.

Earlier this month, a dairy worker in Texas tested positive for bird flu, aka avian influenza, amid an outbreak of the virus among dairy cattle.

It's the first time this virulent strain of bird flu —referred to as highly pathogenic H5N1— has been detected in cows and the first documented cow-to-human transmission of an avian influenza virus, according to the U.S. Centers for Disease Control and Prevention. It's also only the second case of bird flu in a human in the United States.

Is bird flu a problem now?

The multi-state bird flu outbreak is affecting cows in over a dozen dairy farms across the country. Although health officials are on high alert, the current risk to the general public is low, experts say.

While the thought of "bird flu" may sound alarming and stoke COVID-19 pandemic fears, influenza among birds is not new.

“The current bird flu strain that we’re concerned with, H5N1, has actually been circulating around the world for quite some time,” Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center, tells TODAY.com.

What is bird flu?

Bird flu is a disease caused by infection with avian influenza type A viruses. Avian influenza A viruses occur naturally among wild aquatic birds, such as geese, ducks and swans, says Schaffner, but they can also circulate among domestic poultry.

“Bird flu viruses occasionally get into other mammalian species (like pigs). We’ve all heard of swine flu,” Schaffner says. Avian influenza A viruses can also infect horses, bats and dogs, per the CDC — rarely, they spread to humans.

"More recently, we have seen an increase of infections in cattle," Dr. Hilary M. Babcock, infectious disease specialist at Washington University of St. Louis andBJC Healthcare, tells TODAY.com.

This is the first time the avian influenza strain of highly pathogenic H5N1, which causes severe and often fatal disease in birds, has been found in cows. “That’s pretty unusual,” says Schaffner. However, this H5N1 strain does not seem to be making cows very sick, he adds.

What states have bird flu?

Highly pathogenic avian influenza viruses (which include the strain of H5N1 that’s currently spreading)have been detected in the U.S. in wild aquatic birds, commercial poultry and backyard bird flocks beginning in January 2022, according to the CDC.

Overall, 48 states have reported cases of highly pathogenic H5N1.

The current outbreak of H5N1 affecting cows has spread to eight states so far, per the U.S. Department of Agriculture. As of April 11, cases have been reported among dairy herds in:

    Texas

    Kansas

    Michigan

    New Mexico

    Idaho

    Ohio

    North Carolina

    South Dakota

Currently, only one human in Texas is known to have contracted H5N1 in this outbreak, the experts say.

There have been only two human cases of H5N1 in the U.S. ever, says Babcock — the first case was detected in Colorado in 2022 in a person who had direct contact with infected poultry.

As H5N1 surveillance increases, experts anticipate the number of cases among cows to increase. "We’re looking harder now and finding more cases (among cattle) that even 10 years ago would have gone undetected," says Schaffner.

The risk to the general public in the U.S. is low, the experts say. For people exposed due to their line of work, the risk is considered “low-to-moderate,” the World Health Organizagtion said in a statement.

How does the bird flu spread to humans?

"Every once in a while, a bird flu virus can get into a human, but that's rare," says Schaffner. Avian influenza viruses can spread from infected birds to humans in a few ways, according to the CDC:

    Directly from an infected bird

    From environments contaminated with avian influenza virus

    Through an intermediate host, such as an animal

Infected birds can shed the virus in their saliva, nasal secretions, mucus and feces. People can become infected when a large enough amount of the virus gets into the mouth, nose, eyes or is inhaled, says Schaffner.

Transmission to humans typically occurs through close contact with infected birds without protective gear. It can also occur if a person touches contaminated surfaces and puts their hands in their eyes or mouth, or if they breathe in droplets from the air, per the CDC.

It is not immediately clear how the dairy cow infected the person in Texas, the experts note. The only other person who contracted H5N1 in the U.S. was directly involved in the culling of birds presumed to be infected with H5N1, says Babcock.

Sporadic cases of H5N1 in humans have been reported around the world, often in rural areas where people live closely with poultry or other birds. According to the WHO, since 2003 there have been 889 cases and 463 deaths caused by H5N1 in 23 countries.

Once the bird flu gets into a human, “it is almost never spread to anyone else,” says Schaffner. However, “there are ultra-rare instances of transmission from a person very sick with bird flu to a family member or caregiver.”

When does happen, it does not lead to continued spread between people "because the virus doesn’t have the (genetic) capacity to spread easily from person to person,” says Schaffner.

“This strain of bird flu has been around for about a decade and it still has not picked up this capacity to spread readily from person to person, thankfully. ... That should be a matter of reassurance, but also keep us in public health on alert,” says Schaffner.

No human-to-human spread has occurred with the contemporary H5N1 viruses currently spreading in birds, the CDC said.

Can you get bird flu through eggs?

There is no evidence that people can get bird flu from food that’s been properly prepared and cooked, and it is safe to eat eggs, chicken and beef, and drink pasteurized milk, the experts say.

"We have not seen cases that have been from ingesting animal products or animals that may have been infected," says Babcock.

The infected dairy cow herds that have been detected are in quarantine and their milk is being destroyed, says Schaffner.

In a statement, the USDA said the commercial milk supply in the U.S. remains safe. The U.S. Food and Drug Administration said it does not currently have concerns about the safety of pasteurized milk products, including pasteurized cheese.

“The pasteurization process in the U.S. keeps our milk supply very safe,” says Babcock. Pasteurization heats the milk to a high enough temperature to kill bacteria and viruses, including influenza.

Drinking unpasteurized or "raw" milk, which is increasingly trendy, is associated with various infectious disease hazards, says Schaffner. "I discourage people from drinking raw milk,” he adds.

The risk of humans becoming infected by eating eggs from poultry with H5N1 is low, says the FDA, and there safeguards in place to identify infected poultry and remove their eggs from the market.

It's possible for products from infected animals to end up in the food supply, says Babcock, but the risk to humans is still very low. Properly storing and cooking food further reduces that risk.

Although beef cattle are not involved in this outbreak, Schaffner recommends cooking beef to a safe internal temperature. The FDA recommends cooking eggs until the white and yolk are firm.

“There are other reasons that you shouldn’t eat raw eggs (or meat), because these can carry lots of different pathogens," says Babcock.

What happens if a human gets the bird flu?

Bird flu infections in humans can range in severity, the experts note. Some people have zero or only mild symptoms, while others develop severe disease, according to the CDC. "It can be a serious infection with a high mortality rate,” says Schaffner.

The Texas patient had a mild infection, with eye redness as the only symptom, the CDC said. "It was not even a respiratory infection. It was ... conjunctivitis or pink eye," Schaffner notes.

The patient was treated with flu antivirals and is recovering. "We have antiviral medications, the same ones we use to treat regular flu, that work against this avian influenza strain," Schaffner says.

The other human case of H5N1 in the U.S. in 2022 was a mild infection as well, Babcock adds.

Symptoms of bird flu in humans

According to the CDC and experts, the reported signs and symptoms of avian influenza in humans include:

    Fever

    Cough

    Runny nose

    Muscle or body aches

    Headache

    Fatigue

    Shortness of breath

    Eye redness or inflammation (conjunctivitis)

    Diarrhea

    Nausea

Bird flu in humans may look similar to a regular flu or upper respiratory infection, says Babcock, or a person may have no obvious symptoms. It can also lead to pneumonia, respiratory failure and other complications. "There's a full range," she adds.

There is no way to diagnose an infection with bird flu by symptoms alone, the CDC says. Laboratory testing is required.

Can you recover from bird flu?

Yes, you can recover from bird flu. The human recently infected in Texas was treated with flu antivirals and is recovering. The Colorado patient infected in 2022 also recovered.

Globally, bird flu symptoms have ranged from mild to severe, resulting in death in some cases, according to the CDC.

How to prevent spread of bird flu

Although the risk of getting bird flu is low, the CDC recommends the following protective actions:

    Avoid visiting poultry farms if possible

    If visiting poultry farms, wear a mask and avoid touching birds

    Avoid sick or dead birds

    Maintain good hand hygiene

    Do not eat raw or undercooked poultry

    Visit a doctor if you become sick after contact with birds.

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