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'COVID-Arm:' Pfizer And Moderna Vaccines Causing Less Serious But More Common Side Effects

By: John Shumway

PITTSBURGH (KDKA) - While the Johnson and Johnson vaccine remains on the shelf for at least another week, Pfizer and Moderna are picking up the slack.

The blood clot side effect from J&J is extremely rare, but the side effects from Pfizer and Moderna, while less threatening, are much more common.

CBS News Medical expert Dr. David Agus says doctors are seeing a lot of patients experience "COVID arm."

"What COVID arm is is it's a reaction your immune system attacking the spike protein that the vaccines make," he explained. "As part of that, it's manifest by some redness on the arm."

Often, Dr. Agus says, it doesn't happen immediately.

"You can classically be delayed by several days up to a week or so and then it can last for several days," he said. "But it goes away in every patient. It is part of the normal reaction, it is seen much more often in the Moderna vaccine, than the Pfizer vaccine but it's seen in both. And again it's transient. To me, it's kind of a visual manifestation that the vaccine is working. So, myself, as a geek. I think it's amazing to see this because, you know, I know the immune system is hard at work, for protection, but obviously it can be scary for individuals."

The other side effect that is impacting up to 20% of people getting vaccinated is a swelling of the lymph node in the armpit area of the arm that was vaccinated.

Dr. Agus understands that can be alarming.

"No question about it," he said. "It is a way to know when the vaccine is there. Your immune cells travel by a highway, called the lymphatics, and then they get together in big parking garages called lymph nodes. And so when they're reacting to something, they're going to get enlarge those lymph nodes. So while it is scary, It is normal and it will go away and this is part of human physiology."

Dr. Agus continued: "I understand the fear that it can bring to individual patients. Inflammation can last normally about several weeks, which is why we say to women hey listen, let's delay mammogram, too, you know, probably two months after the vaccine because we don't want there to be a false positive. Because they're lymph nodes in the breast, oh my gosh there's something there, can cause a biopsy that you may not need because they will resolve. And so, if you're going to have tests, blood tests, delay the blood test two or three weeks after your vaccine, any scan or imaging study, if you can merge it obviously do it but if you can delay it you should for probably a month or two."

WATCH: A Maskless Summer Ahead?

Despite the J&J setback Dr. Agus is very optimistic about the vaccine program and feels maskless days are now in sight.

"My gut is we're going to wear the mask until this summer," he predicted. "Part of it will be you know again, how much vaccine hesitancy, and are we going to require immunity passports to document that you have been vaccinated and don't need to wear a mask, and that's a big contentious thing. Do we need something on our digital device that can separate the vaccinated versus not?"

Dr. Agus sees that as a hurdle, not a wall, and life will have a much more familiar look by the time we get to the fall.

However, he cautions that optimism has to be tempered by what is going on around the world.

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