The smallpox vaccine effectively induces immunity against mpox virus infection (formerly simian smallpox) in patients with human immunodeficiency virus (HIV) infection, although patients with lymphocyte counts below 500 cells/mm3 require booster doses, according to data from a study published in the Journal of Medical Virology.
The data come from the prospective observational study conducted by researchers at the Infection Biology Laboratory of the Department of Medicine and Life Sciences at Pompeu Fabra University and the HIV Unit of the Hospital del Mar Medical Research Institute in Barcelona, Spain. The investigators analyzed T-cell responses induced by vaccination with JYNNEOS.
Despite the substantial decrease in the reporting frequency of mpox cases from the global peak in August 2022 (30,894 cases) to 804 monthly cases in the last six months of 2023, mpox continues to circulate, and there is no specific vaccine. The JYNNEOS vaccine, with protective cross-reactivity against orthopoxviruses, is approved by the US Food and Drug Administration and the European Medicines Agency for the prevention of smallpox and mpox in adults at high risk for infection.
During the 2022 outbreak in the United States and Europe, vaccine shortages led to the emergency use authorization of a lower intradermal dose. This strategy was aimed at increasing vaccine supply up to fivefold.
Further clinical trials are needed to evaluate responses to JYNNEOS vaccination and compare different administration routes in patients with HIV infection. Protecting this population against mpox is a priority because people with high viral loads or loCD4+ T-lymphocyte counts are especially susceptible to severe disease.
Vaccination Responses
The study assessed the immune response to the JYNNEOS vaccine in patients with HIV who were receiving antiretroviral therapy as outpatients at the Infectious Diseases Unit of Hospital del Mar in Barcelona, Spain. Participants had viral loads controlled by antiretroviral therapy and CD4+ T-lymphocyte counts ≤ 500/mm3 (loCD4 group) or ≥ 500/mm3 (hiCD4 group) in blood. Vaccine responses were compared with those of vaccinated controls without the disease. The study included cases that received the standard subcutaneous vaccine (before August 2022) or the emergency dose-saving intradermal vaccine after its approval in August 2022.
The results demonstrated that the intradermal dose-saving vaccination route is preferable to the subcutaneous route and that patients in the loCD4 group may require at least one booster to generate an efficient response of specific T cells for mpox, wrote the authors.
“This study has two relevant points,” study author Robert Güerri-Fernandez, MD, PhD, head of infectious diseases at the Hospital del Mar Medical Research Institute, told this news organization. “In the subgroup of patients with HIV with effective treatment but without an immune response (ie, loCD4), the vaccine response is worse than in people who have recovered immunity or do not have HIV. Therefore, they need a booster dose.
“The second point is that the intradermal route with one-fifth of the standard subcutaneous dose has a better immune response than the standard subcutaneous route.” He added that it was a good strategy to save doses and be able to vaccinate many more people when vaccine shortages occurred.
“A general conclusion cannot be drawn,” he said. “It needs to be validated with many more subjects, of course, but in some way, it reinforced our confidence in the strategy of health authorities to promote intradermal vaccination. There we had evidence that the patients we were vaccinating intradermally were responding well.”
In Spain, although there is no shortage of vaccines today, they continue to be administered intradermally with a fractionated dose equivalent to one fifth of a standard dose, said Dr. Güerri-Fernandez.
However, in his opinion, observations regarding the two administration routes signal a need for further research. The main message should be that for patients with HIV infection who do not have an immune response, the vaccine response is incomplete, and they need booster doses as well as monitoring of the vaccine immune response, said Dr. Güerri-Fernandez.