Monkeypox Vaccine Wheal: What to Know About the Blister-Like Side Effect

Some people who have received the monkeypox vaccine notice a small, raised bump that appears at the injection site. If this happens to you and the mark persists for days or even weeks, there’s no need to be alarmed: it’s called a weal, a completely normal reaction to be expected. In fact, depending on how your vaccine was given, it is needed – and not seeing it is a bigger problem than seeing it. And, yes, there’s a reason you’re only hearing about it now, months after the monkeypox vaccine rollout began.

In early August, the Biden administration declared the monkeypox outbreak a public health emergency to step up efforts to curb the rapidly accelerating number of cases – 16,900 at press time, according to the Centers for Disease Control and Prevention. (CDC). Prior to the declaration, the preferred monkeypox vaccine, called Jynneos, was administered subcutaneously; that means it was injected into fatty tissue directly under the skin, like the flu vaccine or COVID vaccines, according to the US National Library of Medicine (NLM). As long as monkeypox is considered a public health emergency, the vaccine can be given by intradermal injection, which is not a very common method.

“Most vaccines are given as injections into muscle or subcutaneous fat,” Kaitlyn Rivard, PharmD, director of the infectious disease residency in the department of pharmacy at the Cleveland Clinic, tells SELF. “The monkeypox vaccine is unique in that it is given by injection under the first layer of skin.” Basically, the needle is injected closer to the surface of your skin, between the outermost layers. This injection method should cause that raised, blister-like bump at the injection site.

So why change the way Jynneos is administered now? Giving the monkeypox vaccine by intradermal injection rather than subcutaneously is a way to help preserve the country’s vaccine supply, which is hard to follow with demand due to the rate of spread. “This approach could increase the number of Jynneos vaccine doses available five-fold,” a CDC said. statement said. Subcutaneous administration requires 0.5 milliliters of vaccine while an intradermal injection only requires 0.1 millimeters, a difference that should ultimately help get the most vulnerable people vaccinated.

So what is a papule, anyway? And when can we expect it to disappear? Ahead, experts explain what you need to know about this vaccine side effect.

Why does a wheal develop after the monkeypox vaccine?

The wheal is caused by the contents of the vaccine itself, explains Dr. Rivard. “The vaccine fluid creates a bubble under this shallow layer of skin, which is why it’s noticeable,” she adds. “The bubble should look like a pale rise in the skin,” so it will be similar to the color of your skin tone. Although you may naturally be curious about it, there is no need to worry about this side effect, according to Dr. Rivard: “A papule is a normal phenomenon after an intradermal injection, and there is no no need to worry.”

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