Dose-sparing mpox vaccine regimen is safe and effective

Research presented at the European Society of Clinical Microbiology and Infectious Diseases Global Congress in Barcelona on April 27, 2024, revealed that a dose-sparing mpox vaccine regimen offered the same antibody response as the standard protocol at six weeks, deeming the dose-sparing method as safe and effective.

While mpox originated in West, Central, and East Africa, with the first human cases identified in the 1970s, a recent resurgence of the virus in May 2022 presented a global threat. The 2022 outbreak was tied to the clade IIb strain of the virus, impacting communities far beyond the historically affected regions.

Rapid efforts from the biopharmaceutical industry and FDA helped address this epidemic by approving a mpox vaccine:  the Modified Vaccinia Ankara-Bavarian Nordic (MVA-BN, sold as JYNNEOS) vaccine. The vaccine is a two-dose series given four weeks apart, with maximum protection occurring two weeks after the final vaccine. The CDC recommends the vaccine for certain populations at greater risk of contracting the virus, including men who have sex with men (MSM) and transgender, gender non-binary, or gender-diverse individuals who have had one or more sexually transmitted infections or more than one sexual partner in the past six months. However, much like other highly demanded pharmaceutical products, the mpox vaccines are in short supply.

To address the supply chain issues, the National Institute of Allergy and Infectious Diseases (NIAID), a subset of the NIH, sponsored a study that explored dose-sparing vaccine regimens to extend the existing supply.

The study recruited 225 adults between 18 and 50 years who were not vaccinated against mpox or smallpox across the United States. The randomized study assigned some participants to receive the FDA-approved vaccine regimen, one-fifth of the standard dose or one-tenth of the standard dose. The standard dose was delivered subcutaneously, while the dose-sparing alternatives were injected intradermally. All patients received a two-dose series 28 days apart.

Two weeks after the second dose, those given one-fifth of the standard dose had antibody levels that were comparable to those of the FDA-approved regimen. However, those who received one-tenth of the dose did not have similar benefits.

The NIH press release concluded that “because there are no defined correlates of protection against mpox — immune processes confirmed to prevent disease — these findings cannot predict the efficacy of dose-sparing regimens with certainty. Real-world data from the Centers for Disease Control and Prevention and others have shown similar vaccine effectiveness for the dose-sparing regimen given intradermally and the standard regimen given subcutaneously. A study of the standard MVA-BN regimen in adolescents is ongoing and will report findings later this year.