Vaccination Against Mpox: Does It Work? Is It Safe?
February 15, 2023
By Stan Deresinski, MD, FACP, FIDSA
Clinical Professor of Medicine, Stanford University
SYNOPSIS: Vaccination, either subcutaneously or intradermally, with the non-replicating Jynneos vaccine is safe and effective.
SOURCES: Payne AB, Ray LC, Cole MM, et al. Reduced risk for mpox after receipt of 1 or 2 doses of JYNNEOS vaccine compared with risk among unvaccinated persons — 43 U.S. jurisdictions, July 31-October 1, 2022. MMWR Morb Mortal Wkly Rep 2022;71:1560-1564.
Duffy J, Marquez P, Moro P, et al. Safety monitoring of JYNNEOS vaccine during the 2022 mpox outbreak — United States, May 22-October 21, 2022. MMWR Morb Mortal Wkly Rep 2022;71:1555-1559.
Jynneos (Modified Vaccinia Ankara vaccine, Bavarian Nordic) is a live, nonreplicating viral vaccine licensed for the prevention of smallpox and monkeypox (mpox) in adults age 18 years and older, administered as a 0.5-mL two-dose series given 28 days apart by subcutaneous injection. Faced with possible shortage concerns, the FDA issued an emergency use authorization on Aug. 9, 2022, for administration of just 0.1 mL by intradermal injection for adults age 18 years and older.
The efficacy of the JYNNEOS vaccine was evaluated in an analysis of vaccination status among 9,544 cases of mpox in men age 18-49 years. The incidence per 100,000 was 7.4 times higher (95% CI, 6.9-9.1) in unvaccinated individuals compared to those who had received a single vaccine dose more than 14 days earlier.
Compared to those who had received a second dose more than 14 days earlier, the incidence in the unvaccinated was 9.6 times higher (CI, 6.9-13.2). There was no apparent difference in efficacy between subcutaneous and intradermal administration.
Almost 1 million doses of the vaccine were administered in the United States from May 22, 2020, to Oct. 21, 2022, with the Vaccine Adverse Event Reporting System (VAERS) receiving 1,350 events. Of these, an administration error accounted for 47% of the reports (only 2% of these had an associated adverse health event), and these errors were significantly more frequent after intradermal than subcutaneous administration, with absence of a wheal accounting for 54% of those associated with intradermal administration.
Overall, an adverse health event accounted for 51% of reports, with similar frequency among those with subcutaneous and intradermal injection. Only 14 reports were considered serious (none in individuals younger than age 18 years), and these included two deaths within two days of vaccination, with one attributed to drowning and the other lacking information. Nine vaccines required hospitalization: two each for myocarditis and pericarditis, and one each for appendicitis, aseptic meningitis, atrial fibrillation, idiopathic thrombocytopenic purpura, and methemoglobinemia.
The remaining three were cases in which the vaccines reported disability or permanent damage from the following in one each: injection site discoloration, injection site pain, and injection site scar. The rate of myocarditis reports per million was 1.53 after one dose and 2.99 after two doses. There were three reports of anaphylaxis occurring within 24 hours of vaccination.
COMMENTARY
These data indicate the non-replicating Jynneos vaccine is both safe and effective. Although self-reporting, upon which VAERS relies, is not the optimal means to assess vaccine safety, there was a lack of any signal indicating a significant risk of adverse events. This suggests that even with formal prospective monitoring, the vaccine is sufficiently safe to warrant its ongoing use.
At the same time, the data indicate the vaccine is effective in prevention of mpox even after a single injection. The FDA’s decision to allow reduced-dose intradermal rather than subcutaneous administration to stretch the vaccine supply was met with some concern, but the CDC now reports this route was efficacious.
Vaccination, either subcutaneously or intradermally, with the non-replicating Jynneos monkeypox vaccine is safe and effective.
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