As cases of mpox, the disease caused by the monkeypox virus, climb in New York City, health professionals and the city Department of Health and Mental Hygiene (DOHMH) have urged people at high risk of contracting the virus to receive the vaccine. DOHMH is making appointments for the vaccine available as quickly as possible, but the vaccine remains in extremely short supply nationwide. Richard Silvera, MD, MPH, Assistant Professor of Medicine (Infectious Diseases), at the Icahn School of Medicine at Mount Sinai, explains what the vaccine is and who should consider getting a shot.
Has a vaccine been approved by the FDA for mpox, and if so, when?
There are two vaccines approved by the U.S. Food and Drug Administration for mpox and smallpox, which are in the same Orthopoxvirus family. JYNNEOS, initially approved in 2019, is currently being used for mpox vaccination efforts. The other is ACAM2000, which was approved in 2007.
How do the vaccines work?
The JYNNEOS vaccine is approved to be administered as two shots subcutaneously, or into tissue under the skin, delivered at least four weeks apart. On August 9, the FDA granted emergency use authorization for the vaccine to be delivered intradermally, or between layers of the skin, to increase availability of doses up to fivefold. DOHMH adopted this guidance on August 23.
ACAM2000, which is not being used for the current outbreak, is administered as a single dose via multiple punctures into the skin using a bifurcated needle.
Both vaccines contain live vaccinia virus, which is also an Orthopoxvirus like mpox. The JYNNEOS vaccine contains attenuated virus. “What that means is there is a virus in the vaccine that has been medically altered to prevent it from reproducing,” Dr. Silvera said. Vaccinated individuals are unable to pass on vaccinia infections to other people around them, unlike with replication-competent vaccines such as ACAM2000.
The vaccine elicits two types of immunities: humoral and cellular, said Dr. Silvera. Humoral immunity involves the building of antibodies that fight off viruses if the body is exposed to them. Cellular immunity involves teaching cells to recognize cells that are infected with viruses and to eradicate those cells. Vaccinia virus has been used as a vaccine for nearly two centuries to fight off more lethal infections, such as smallpox, which was considered eradicated in the United States in the late 1970s.
Is intradermal administration of the vaccine as effective and safe as subcutaneous?
The guidance for intradermal administration of the JYNNEOS vaccine is only for those ages 18 and older. Individuals who are younger would still require the subcutaneous route.
The authorization was granted based on data of a 2015 clinical study that evaluated a two-dose intradermal regimen compared to a subcutaneous one, with the former administered at one-fifth the volume of the latter route of administration.
Results demonstrated that intradermal administration produced a similar immune response to subcutaneous administration. Administration by the intradermal route resulted in more redness, firmness, itchiness, and swelling at the injection site, but less pain, and that these side effects were manageable.
As per the Centers for Disease Control and Prevention (CDC), the city Health Department has adopted the guidance of using subcutaneous delivery to individuals with a history of developing keloid scars. These are raised scar tissue that might occur after a cut or a skin injury.
Am I protected with the first shot? How effective is the vaccine?
“The vaccine does offer some protection after the first shot, but it takes about two weeks after the vaccine is given before that protection comes into play,” said Dr. Silvera. When the two-shot series is complete, it confers about an 80-85 percent effectiveness against infection at the individual level, but its effectiveness at a community level is currently unknown, he added.
Given limited supplies of the JYNNEOS vaccine, the DOHMH is delaying second doses so that more people can get first doses and have some protection. In DOHMH guidance, it added that it is OK to wait longer than four weeks to receive the second dose. Those who received the first dose will be contacted by the Health Department when second doses are available.
Who is considered high-risk and should consider getting the vaccine?
The city is prioritizing appointments for high-risk groups, which currently include men who have sex with men and transgender or gender non-conforming/non-binary people, if they have had multiple or anonymous sex partners in the last 14 days, and transactional sex workers of any sexual orientation or gender identity.
That guidance may change as the epidemic evolves, Dr. Silvera said, adding that health officials are watching the situation closely.
Mpox, however, should not be stigmatized as a sexually transmitted infection unique to the LGBTQ community, Dr. Silvera pointed out. Infections are spread via intimate skin-to-skin contact and sex happens to be one such activity. “No particular person is at high risk of contracting an infection because of who they are,” he stressed.
Who should not get the vaccine?
People who have an allergy to the ingredients of the JYNNEOS vaccine should not receive it. The ingredients include gentamicin, ciprofloxacin, and egg protein.
Otherwise, people who meet the eligibility criteria should highly consider the vaccine, Dr. Silvera said.
If I had received a routine smallpox vaccine, am I still protected against mpox today?
Up until 1972, the United States had routine smallpox vaccination, which led to the disease being eradicated. However, people who received a smallpox vaccine then would not be considered to have adequate protection against the current mpox outbreak, Dr. Silvera said, adding that if those individuals meet the criteria for getting the JYNNEOS vaccine, they should seek it.
The CDC guidance, however, stipulates that people who previously have been vaccinated against smallpox can receive just one dose of the JYNNEOS vaccine for adequate protection.
Can I receive a mpox vaccine around the same time as a COVID-19 shot or booster?
The current recommendation is to space out four weeks between receiving a JYNNEOS vaccine and a COVID-19 shot or booster that uses mRNA technology, such as those from Pfizer or Moderna. “That’s to help prevent people from any adverse side effect,” Dr. Silvera said.
However, if vaccination is recommended due to a known exposure to mpox, the individual is encouraged to get the JYNNEOS vaccine even if the person recently received a Pfizer or Moderna vaccine, according to city Health Department guidance.
The story has been updated to include that DOHMH has adopted the guidance regarding administering the mpox vaccine intradermally.