Smaller Doses of Monkeypox Vaccine Elicits Equal Immune Response in People Living With, Without HIV


The study results also determined that those who were previously vaccinated against smallpox had a 2.7 times higher immune response than those who were not previously vaccinated.

Study results demonstrated an insignificant difference in the strength of the immune response between patients who received their 2-dose monkeypox (mpox) vaccine injections in small doses intradermally and those who received their vaccine as prescribed in full-dose injections subcutaneously.

Health care worker filling a syringe needle

Image credit: MargJohnsonVA |

The smaller doses of the mpox vaccine—which are approximately one-fifth of FDA-approved full dose and spread out as long as 3 months—were designed to stretch the short supply of vaccines available after the outbreak in May 2022. Mpox is spread through bodily fluids, skin-to-skin contact, and sexual intercourse. About 145 participants from New York who were vaccinated against mpox were enrolled in the study, of which the majority were men (81%) and identified as being in the LGBTQ+ community (89%). In addition, 35 participants (24%) were people living with HIV and 29 (20%) had previously been vaccinated against smallpox.

According to the authors, people living with HIV are at a higher risk of contracting mpox due to their weakened immune systems and vulnerability to co-infection; however, the investigators did not find differences in the magnitude of the immune response between vaccinated people living with HIV and vaccinated people who are HIV-negative.

“Our study shows that smaller vaccine doses of mpox vaccine administered in 2 doses, spread out over weeks to months, were similar to the full subcutaneous FDA-approved dose,” said study co-lead investigator Angelica Cifuentes Kottkamp, MD, infectious disease specialist and assistant professor at NYU Langone Health’s department of medicine, in a press release. “Implementing the smaller dose was a good emergency measure in the face of immediate shortages of the vaccine.”

Immune response was gauged by the amount of detectable immunoglobulin G (IgG) antibodies, the immune proteins which help kill the mpox virus. The study results determined that those who were previously vaccinated against smallpox had a stronger immune response, with detectable IgG antibody levels in blood samples being approximately 2.7 times higher compared to those who were not previously vaccinated for smallpox. Additionally, the IgG antibodies were detected in some cases more than 6 months after individuals received the second and final doses of the vaccine.

According to the investigators, more research is necessary to determine whether additional vaccine doses against mpox are for optimal protection and how long protection lasts. Further, the amount of emergency vaccines available as well as the ability to increase production quickly in case of future outbreaks also need to be examined.

“Our findings offer valuable support to the people most at risk of being infected with mpox so that in the case of an mpox resurgence, infectious disease specialists have sufficient vaccination tools and knowledge to deal with it effectively in the short term,” said study senior investigator Mark Mulligan, MD, Thomas S. Murphy professor, Department of Medicine at New York University (NYU) Grossman School of Medicine; director, NYU Langone Vaccine Center; and director, Division of Infectious Diseases and Immunology, NYU Langone Health, in the press release.


NYU Langone Health/NYU Grossman School of Medicine. Mpox (monkeypox) vaccine triggers equally strong immune response in smaller than usual doses and in people with or without HIV. News release. December 13, 2023. Accessed January 2, 2024.

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