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I'm eligible for the COVID vaccine and due for a mammogram. Which should I do first?

 due for a mammogram. Which should I do first?

, associate professor of radiology at Duke University. But if you can, 

schedule the mammogram either before the vaccine or 4-6 weeks after the second dose

, in keeping with new recommendations from the Society of Breast Imaging.

That's because swollen lymph nodes are both a common side effect of the vaccines and can also be a marker of early breast cancer, he says — especially when lymph nodes on only one side are swollen.

"It can be the only sign we see," he says, noting that a mammogram often detects swelling that a person wouldn't notice. Of course, other things cause lymph nodes to swell, such as colds – swollen nodes shouldn't cause anyone to jump to the conclusion that they have cancer. But "when we see one, it triggers us to work it up and figure out what's going on," Grimm says.

And as soon as people started getting vaccinated, breast radiologists started noticing a big uptick in the number of women with swollen lymph nodes on one side of their body. They started asking patients whether they'd had the vaccine recently. Now he and his colleagues see vaccine-related swollen lymph nodes every day. The day we talk to him, two of the three patients he'd seen that morning had shown swollen lymph nodes on one side.

The good news? Most people can adjust their vaccine and mammogram schedules accordingly. Even if you can't, Grimm encourages you to pursue both. Worst case scenario? "They might ask you to come back and take more pictures and make sure it's resolved," he says. "It's a pretty low-key thing."

I've heard that the ingredients in the COVID vaccines are dangerous. Even if this is a rumor, I'd love to know what's actually in there!

Anti-vaccination groups have historically propagated false information about the ingredients in vaccines, and the COVID vaccine is no exception. We asked 

, professor of medicine at the Mayo Clinic in Rochester, Minn., and co-director of the Vaccine Research Group, to explain exactly what each ingredient in the two vaccines licensed in the U.S., 

 This is the only "active" ingredient in the two vaccines, i.e. the ingredient that provokes the desired medical response. mRNA (messenger-RNA) is a short stretch of RNA that tells cells to make a protein, Kennedy explains — in this case, the now-famous spike protein we've all seen so many pictures of. That's what triggers the immune response. And it's similar to the mRNA that's floating around in our cells all the time, he says.

Vaccine critics have raised concerns that these vaccines could enter a cell's genome, and cause unexpected problems. For that to happen, the vaccine mRNA would have to enter a cell nucleus, and according to data from the manufacturers, it doesn't. Even if it did, many scientists say the possibility of an mRNA entering nuclear DNA is low. 

The mRNA is identical in the Pfizer and Moderna vaccines.

"Normally your cells don't like foreign RNA, so they vaccine manufacturers have tweaked it to be stable," Dr. Kennedy says. Manufacturers needed to make the mRNA last several hours in your cells, giving the vaccine time to make enough protein for your body to respond to.

One way they've done that is by adding lipids, molecules made from fats that don't dissolve in water. Both vaccines contain a variety, including cholesterol and polyethylene glycol-2000 (affectionately known as PEG2000) and some "alphabet soup" molecules with names such as 

1,2-distearoyl-snglycero-3-phosphocholine [DSPC]

. "Basically they act like little droplets of oil, and the RNA is floating inside," Kennedy says. This serves two purposes, he adds: It stabilizes and protects the RNA, and it helps the RNA get through the cell membranes .

The Pfizer vaccine uses salts to maintain the right acidity inside cells. Moderna uses a mixture of mild acids and bases to do that.

These ingredients are commonly used as buffers in other injectable medicines, Kennedy notes. "They make sure that the pH of the vaccine matches the pH of your body and make sure that it won't damage cells when the liquid is injected."

Without an ingredient like sugar, water molecules form crystals that can act like razor blades. "So the sucrose blocks how those crystals form so they don't chop anything up," Kennedy says.

Most of the liquid in the vial is saline solution.

What's not in the vaccine, Kennedy notes, is any live or dead virus. And since these vaccines are made in machines, they're easier to keep sterile than other types of vaccines, which are made using living cells. While researchers aren't yet sure why a small percentage of people who get the vaccine experience allergic reactions, he says many people suspect it's that PEG2000 lipid, which is also found in everything from laxatives to cosmetics to toothpaste.

The bottom line? "The disease has a known mortality rate between 1 and 2 percent," Kennedy says. "If the vaccine were as dangerous as the disease, we should see 34,000 people dying from the vaccine every day."

My dog can't resist sniffing a discarded mask on the street. How risky is that?

Dog-walkers on oft-trodden streets know the perils of the fallen mask.

, chief veterinary oficer of the North American Veterinary Community, says the risk of contracting COVID-19 from such an encounter — both for you and your dog — is "extremely unlikely."

Preliminary research demonstrates that dogs are fairly resistant to infection, Varble says. And even if viral particles did get onto your dog's pelt or body, it would be difficult for you to contract the disease through surface-level, or physical, transmission. You'd have to touch the dog, pick up the particles from the fur and bring them to your eyes, nose or mouth.

Nonetheless, if you're eager to be extra safe — and to avoid a potential nightmare scenario arising from your dog's mask-sniffing escapades — there are a couple things you can do.

"For one, always have your dog on a leash," Varble suggests. "And take careful diligence to keep them away from strewn masks."

One idea is to look for dog paths or less crowded streets to walk your dog where litter is less of a problem. If you do see your dog sniffing a mask, Varble says, usher them away from the area as quickly as possible. Do your best not to make contact with the mask directly.

In the worse-case scenario, you might need to use your hands to pull the mask out of your dog's mouth. You could carry disposable gloves for these occasions. But even then, 

, an assistant professor of medicine at Duke University, and Varble agree that your first priority should be to wash your hands with soap and water ASAP! And keep hands away from your face and mouth prior to washing.

Finally: "If you see your dog walk over a mask, something as simple as baby wipes can help to decontaminate fur and feet," Varble adds. "Just be careful around your dog's eyes, nose and mouth and wipe off feet and face softly."

Sheila Mulrooney Eldred is a freelance health journalist in Minneapolis. She's written about COVID-19 for many publications including Medscape, Kaiser Health News, Science News for Students and 

Pranav Baskar is a freelance journalist who regularly answers coronavirus FAQs for NPR.

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Pranav Baskar

Are there issues with having a mammogram right after a vaccine? Is there a list of vaccine ingredients — some people say they're scary. Also: My pooch loves to sniff discarded masks. Should I worry?

Coronavirus FAQs: Mammograms, vaccine ingredients... and dogs who sniff masks

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