Colorized transmission electron micrograph of monkeypox particles (red) found within an infected cell, cultured in the laboratory. Credit: NIAID. (Wikimedia Commons)

In the current monkeypox outbreak, the pandemic-strained U.S. public health system is once again faced with a major threat. This time, a vaccine is already available, but only in limited quantities. Here’s what nurses need to know. It will remain important to keep up with new developments as they occur.

The Jynneos vaccine

Jynneos is a live but nonreplicating vaccine for the prevention of both monkeypox and smallpox. It is made from vaccinia virus, a less virulent relative of these two viruses. The vaccine is given subcutaneously in two separate doses administered at least 28 days apart, and a person is considered fully vaccinated two weeks after the second dose.

The most common vaccine side effects are pain, redness, induration, swelling, or itching at the vaccination site. (People with HIV infection or atopic dermatitis do not seem to experience additional or more severe side effects.) Jynneos is considered safe for people who are immunocompromised, though the vaccinated person may not mount a full immune response.

Who should be vaccinated?

The vaccine is used for postexposure prophylaxis of people who have been exposed to a suspected or confirmed case of monkeypox, or for pre-exposure prophylaxis of people in high-risk groups. Because 99% of global cases in the current outbreaks have been in men who have sex with men, the vaccine is prioritized for men who have sex with men and who report having had multiple and/or anonymous sex partners in the prior 14 days.

An initial vaccine dose within four days of exposure may prevent disease. If given within five to 14 days of exposure, it may not prevent the illness but can decrease the severity of infection.

Why aren’t there enough vaccines yet?

There are an estimated 1.6 million adults in the U.S. who are considered to be at greatest risk of acquiring monkeypox, so a total of 3.2 million doses are needed to vaccinate all of these people. The Biden-Harris administration states that in addition to the 56,000 doses available from the strategic national stockpile, another 240,000 doses are expected “in the coming weeks.” By the end of the year, an estimated 1.6 million doses will be available in the U.S.

The Biden administration has been criticized for not ordering more vaccination when cases first began to appear. While even a handful of non-travel-related cases outside of Central and West Africa was cause for concern, no large and widespread outbreaks had ever been reported. (One of the largest occurred here in the U.S. in 2003, when 71 people were infected by pet prairie dogs who had been infected after being housed with animals from Ghana.)

To make matters more difficult, according to Health Policy Watch, the world’s only production facility for monkeypox vaccine, Bavarian Nordic in Denmark, was in the midst of a planned shutdown for expansion at the time monkeypox cases began to emerge in May. Since then, expedited plant inspections by the FDA and European drug authorities have ensured greater manufacturing capacity as the plant reopens.

Meanwhile, Africa, where monkeypox is endemic, still has received none of the world’s limited current supply of monkeypox vaccine.

Jynneos dosing strategies.

Various workarounds to the limited vaccine availability are being attempted. In the U.S., Canada, the U.K. and elsewhere, public health officials have been prioritizing one dose of vaccine administered to as many people as possible in order to mitigate the severity of cases, with a second dose to be administered when supplies increase.

Intradermal use of Jynneos at lower doses. On August 9, the FDA issued an emergency use authorization (EUA) to allow Jynneos to be administered intradermally instead of subcutaneously.  Intradermal injection requires only one-fifth of the subcutaneous dose, greatly multiplying the number of doses available.

The intradermal dose results in more redness, itching, and swelling than the subcutaneous dose. Those who administer the vaccine by this route will need to be scrupulously accurate in their technique. If this tiny dose ends up in subcutaneous tissue, the vaccine may not provide protection.

Other available vaccines?

ACAM2000, an older smallpox vaccine that could protect against monkeypox, is available in the Strategic National Stockpile in case smallpox is deployed as a biological weapon. It is “replication competent”—a live vaccinia virus that poses a risk to both the vaccine recipient and to unvaccinated people who might contact the fresh vaccine wound. (This is the smallpox vaccine some readers may remember, which is administered via several punctures from a bifurcated needle, and generally leaves a scar about the size of a dime at the site of injection.)

ACAM2000 may cause myocarditis and pericarditis in the recipient. Immunocompromised recipients and those with skin conditions such as eczema, dermatitis, or psoriasis are at increased risk of complications, some life-threatening, from this vaccine. Unvaccinated people who are pregnant, immunocompromised, or have heart or serious skin conditions and are accidently infected via the vaccine wound are also at risk for serious complications.

While some have suggested that the nation’s supply of ACAM2000 be deployed at this time, the risk/benefit of a vaccine with many potential complications, some fatal, is different for monkeypox (not deadly, in most cases) than for smallpox, which has a mortality rate of 25% or more in those who are not immune.

For more information on monkeypox, see the author’s two previous posts: