The last U.S. monkeypox outbreak happened in 2003. With the current outbreak in 2022, almost all U.S. states have reported monkeypox cases.
There are two licensed vaccines available in the U.S. to prevent monkeypox. This includes ACAM2000 and JYNNEOS. But only certain people are eligible to receive one.
People with known monkeypox exposure may be eligible for vaccination. The same goes for certain people with risk factors for monkeypox exposure. Check with your healthcare provider or local health department for vaccine eligibility.
Is it a mosquito bite, a pimple, or monkeypox? You may be asking yourself this question as monkeypox cases are spreading across the U.S. The last outbreak here was in 2003, with 47 confirmed and probable cases. Today, there are monkeypox cases reported in almost all U.S. states.
The good news is that we have vaccines that can help prevent monkeypox. This includes smallpox vaccines that offer cross-protection against the monkeypox infection. But at least for now, only certain people are eligible to get one. So, who does this include, and what are the options?
Monkeypox is an infection caused by the monkeypox virus. Most cases happen in Africa, but they’ve occasionally been reported elsewhere. Currently, scientists are tracking an outbreak extending into multiple countries, including the U.S.
You may have heard that monkeypox only spreads through sex. But this isn’t true. It typically spreads through large respiratory droplets or contact with an infected person’s bodily fluids or skin lesions. This can include long periods of face-to-face contact and touching contaminated clothing or linens.
After exposure, symptoms can show up as early as 5 days, or as late as 21 days. The hallmark sign of monkeypox is a rash that spreads to different areas of the body. Before this happens, some people develop symptoms that include fever, headache, and/or swollen lymph nodes.
Over the course of about 2 to 4 weeks, the rash will typically progress from red bumps to pustules that scab over. You’re no longer considered contagious once the rash has fully healed, the scabs have fallen off, and a fresh layer of skin has formed.
The short answer: No.
But the viruses that cause monkeypox and smallpox belong to the same group (genus) of viruses, called Orthopoxvirus. Smallpox is caused by the variola virus. Along with the monkeypox virus, it’s one of several Orthopoxviruses that can infect people.
Yes. Vaccines that protect against smallpox can also be used to prevent monkeypox.
You may be surprised to learn that the available smallpox vaccines don’t actually contain the variola virus. Instead, they contain the vaccinia virus, another Orthopoxvirus that causes milder disease. The vaccinia virus offers cross-protection against smallpox. And this cross-protection can also extend to monkeypox.
However, we don’t know yet how well these vaccines work during this current outbreak.
ACAM2000 was first licensed to prevent smallpox in 2007. It took the place of Dryvax, one of the vaccines used to eradicate smallpox. Currently, it’s also being used to prevent monkeypox.
ACAM2000 contains a live vaccinia virus. This virus causes a localized infection, which triggers an immune response. Antibodies and other memory cells are created during this process. They’ll be able to recognize and fight the monkeypox virus if you’re exposed to it in the future.
The U.S. stopped vaccinating the general public against smallpox in 1971. But if you received one before that time, you likely have a scar to prove it. ACAM2000 works in a similar way. To receive your dose, a two-pronged needle is dipped into a vaccine solution. It’s then used to puncture an area of skin on your arm multiple times.
Within 3 to 4 days of getting vaccinated, the virus should cause a red, itchy sore spot (lesion) where it was given. This spot will blister and scab over to leave a scar. It’s important to keep this area clean and covered to avoid spreading the virus to others.
If you don’t develop a lesion that scars over, it could mean your vaccination was unsuccessful. But if the vaccine “takes,” you’ll typically develop the greatest amount of protection after about 4 weeks.
Aside from puncture site side effects, you may experience:
Swollen lymph nodes
Although uncommon, myocarditis (heart inflammation) and pericarditis (heart lining inflammation) have been reported after vaccination.
Remember: The vaccinia virus is different from the variola virus. So, you can’t get smallpox (or monkeypox) from the vaccine. But since it contains a live virus that can cause an infection, certain people shouldn’t receive it.
ACAM2000 may not be an option for people with:
Severely weakened immune system (including those taking immunosuppressants)
Eye disease treated with topical steroids
Current (or history of) atopic dermatitis or eczema
Infants under 12 months of age
JYNNEOS was first licensed to prevent smallpox and monkeypox in 2019. It also contains a live vaccinia virus. But unlike ACAM2000, the virus isn’t able to make copies of itself. And it doesn’t result in the same scar, either. However, it still teaches your immune system to recognize the monkeypox virus.
JYNNEOS is given as a two-dose series, 4 weeks apart. You’ll receive it as an injection under the skin, or into the topmost layer of skin of your upper arm. And you should develop the highest amount of protection 2 weeks after your second dose. So, it’ll take a few weeks longer to build up immunity compared to ACAM2000.
Common JYNNEOS side effects include:
Injection-site reactions (like pain, swelling, redness)
Since the vaccinia virus in JYNNEOS isn’t able to copy itself, it may be the preferred option for certain people who can’t receive ACAM2000. This includes people living with HIV or atopic dermatitis.
Smallpox was declared eradicated in 1980. But the U.S. has millions of smallpox vaccine doses stockpiled in case they’re ever needed. Even so, monkeypox is an evolving issue in the U.S. And doses are currently being allocated to areas with a higher number of cases.
Who can get vaccinated against monkeypox may change over time. But as of July 2022, you may be eligible if:
You’ve had known exposure to someone with monkeypox. It’s recommended to receive a vaccine within 4 days of exposure to prevent infection. Getting it between 4 and 14 days may help lessen symptoms, but may not prevent infection.
You have risk factors that make monkeypox exposure more likely. This includes having a sexual partner in the last 14 days who was diagnosed with monkeypox, or multiple sexual partners in the last 14 days in an area with known monkeypox cases.
You have a job that puts you at high risk of monkeypox exposure: This applies to lab personnel who do monkeypox testing and certain healthcare workers.
You meet state- or region-specific criteria. Due to limited vaccine supply, certain states or regions may have their own eligibility requirements. For example, certain people taking PrEP for HIV may qualify for a vaccine in Los Angeles county.
If you’re vaccinated after known monkeypox exposure, this is called post-exposure prophylaxis (PEP). The vaccine helps prevent an infection after you’ve been exposed to the virus. And the sooner you get it, the better.
If you’re vaccinated because you’re more likely to have been recently exposed, this is called PEP++ (or expanded PEP). It’s a similar concept to PEP, but there may not be documented exposure to monkeypox.
If you’re unsure if you fit into one of these categories, contact your healthcare provider or local health department. They can help determine your vaccine eligibility, which vaccine you should get, and where you can get it.
You’re still eligible to get vaccinated against monkeypox, even if you’ve gotten a smallpox vaccine in the past. That’s because you may not be protected anymore, especially if you were vaccinated decades ago.
ACAM2000 and JYNNEOS are two licensed vaccines that can be used to help prevent monkeypox. Doses are being allocated to areas with more cases, and only certain people are eligible to get vaccinated.
Contact your healthcare provider or local health department if you have been exposed to monkeypox, or if you think you’re at higher risk of exposure. They can help determine your eligibility.
Centers for Disease Control and Prevention. (2017). Vaccinia (smallpox) vaccines: For healthcare providers.
Centers for Disease Control and Prevention. (2021). History of smallpox.
Centers for Disease Control and Prevention. (2022). 2022 U.S. map & case count.
Centers for Disease Control and Prevention. (2022). Clinical recognition.
Centers for Disease Control and Prevention. (2022). Considerations for monkeypox vaccination.
Centers for Disease Control and Prevention. (2022). Frequently asked questions.
Centers for Disease Control and Prevention. (2022). Past U.S. cases and outbreaks.
Centers for Disease Control and Prevention. (2022). Vaccination administration considerations for specific populations.
Centers of Disease Control and Prevention. (2022). Vaccines | Monkeypox.
Emergent Product Development Gaithersburg Inc. (2018). ACAM2000 [package insert].
Frey, S. E. (2014). New smallpox vaccines for an ancient scourge. Missouri Medicine.
Los Angeles County Department of Public Health. (n.d.). Monkeypox.
McCollum, A. M. (2019). Smallpox and other orthopoxvirus-associated infections. CDC Yellow Book.
U. S. Department of Health and Human Services. (2022). JYNNEOS monkeypox vaccine distribution by jurisdiction.
U. S. Food and Drug Administration. (2018). ACAM2000 (smallpox vaccine) questions and answers.