You have a lump on your arm weeks after monkeypox vaccine. Why it's a 'super common' side effect.

If you've gotten vaccinated for monkeypox, you may be familiar with "the lump." 

Ever since the viral outbreak reached the U.S. this summer, many people have taken to social media to report side effects of the Jynneos vaccine, which can be injected intradermally (into the skin) or through the more traditional subcutaneous method (below the skin).

One common complaint is a red bump at the injection site lasting for two to three weeks, if not longer. But experts reassure that it's not a "weird" or "permanent" reaction. 

A temporary lump on your arm is normal for any vaccination, but "it is particularly expected with the Jynneos vaccine," says Anthony Fortenberry, chief nursing officer at Callen-Lorde Community Health Center. "This is a super common side effect." 

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What causes the bump? 

Induration, or an area of hardness at the injection site, is part of the body's immune response to vaccines. 

"The body recognizes the viral material as foreign and sends immune cells to react against it," says Dr. Aditya Chandorkar, an assistant professor in the division of infectious diseases and international medicine at the University of Minnesota. "One of the consequences of this reaction (is) some degree of local reaction, leading to a lump/swelling.

"It’s important to note that the presence or absence of the swelling is not a marker for how well the person is going to be protected by the vaccine." 

Are there ways to treat it? 

Some people have reported tenderness, itching, pain or bruising on or around the lump. "That generally does resolve on its own," Fortenberry says. "You do want to avoid scratching it because that can cause further inflammation, delay healing and also cause infection, so you want to be cautious. And if it's causing pain, the recommendations are over-the-counter Tylenol or Motrin" to help with inflammation. 

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How long does it take to go away? 

"Having a large, painless lump at the site of the injection is fairly common," Chandorkar says. "The original (Jynneos) vaccine studies reported some degree of local swelling in over half of the people who received the vaccine." Anecdotally, "most people have reported the lump going away after a week to two weeks. In almost all cases, the lump should go away by itself, and people should not need to see their physician." 

Can I still get the second dose if I have a lump? 

If the bump is still present after more than two weeks, that's no cause for alarm. In fact, it's "really common," Fortenberry says, and should not deter people from receiving their second Jynennos dose four weeks after the first. 

"So many people are having inflammation at the site for many weeks," Fortenberry says. "For inflammation to occur for up to four weeks is such an expected side effect that clinical guidance (at vaccination sites) addresses that, by asking nurses to administer the shot on the other arm."

What are other reactions to the Jynneos vaccine? 

"Other side effects include muscle pain, headache, fatigue and nausea," Chandorkar says. "Although fevers and chills are reported, they are not the norm. They are only seen in 1% to 10% of patients."

The Jynneos vaccine produces side effects that "are comparable to most other vaccines," he adds. "(Reactions are) generally far milder than what some experienced with the COVID-19 vaccines." 

When should you see a doctor? 

You should speak to a medical professional if you experience fevers or chills for more than one to two days after getting the Jynneos vaccine, says Dr. Peter Hotez, co-director of the Center for Vaccine Development at Texas Children’s Hospital and dean of the National School of Tropical Medicine at Baylor College of Medicine.

As for the lump, "if the pain becomes problematic, or if you see the redness worsen or spreading, including streaks of redness, you should contact your doctor," Hotez says. 

Fortenberry stresses that severe adverse reactions to the Jynneos vaccine are "extremely rare," but you should call 911 immediately if you experience difficulty breathing, hives, swelling of the face or throat, a fast heartbeat, dizziness, or weakness after getting vaccinated. 

Why is it important to get vaccinated? 

Although side effects such as the lump might seem like a nuisance, they're much better than the alternative of getting monkeypox, which is an extremely painful infection with symptoms that can last two to four weeks and requires quarantine. 

"The best way to ensure you won't become infected is to get vaccinated," Hotez says. "Monkeypox, although rarely fatal, is a serious and debilitating infectious disease, and could require hospitalization." 

And if you have any fears of potential side effects, don't hesitate to discuss them with medical personnel at your vaccination site. 

"They have all the information necessary to provide reassurance and make sure everyone has very clear expectations around the vaccine," Fortenberry says. "We encourage everyone to complete their vaccine series if they're eligible for a second dose. Don't let side effects prohibit you from going back for your second dose and getting full immunity. It's super important to err on the side of reaching out to a medical provider if you have questions or concerns – that's what we're here for. 

"You don't have to manage this on your own with the internet."