New York, Dec 14 (IANS): Delivering the two-dose Mpox vaccine, called JYNNEOS, in smaller than the usual FDA-approved doses, produced a detectable immune response, regardless of whether people were living with or without HIV, according to a new study.

The effect was also seen when injections were administered between layers of the skin rather than by the standard route under the skin.

The smaller doses, about one-fifth of the usual full dose and spread out by as long as three months, were designed to stretch the short supply of vaccine available after an outbreak in May 2022.

The study on 145 New Yorkers showed no significant difference in the strength of the immune response (as gauged by the amount of detectable IgG antibodies, immune proteins that help kill the mpox virus) between most of those who received their vaccine injections in small doses between layers of the skin (intradermally) and those who received it as prescribed in full-dose injections just beneath the skin (subcutaneously).

Infact, the researchers from the NYU Grossman School of Medicine found that people fully vaccinated with two smaller doses had an immune response four times stronger than those who did not complete the vaccination series and had only one dose.

The IgG antibodies were detected in some cases more than six months after a second and final dose of the vaccine, they revealed in the study published in the New England Journal of Medicine.

"Our study shows that smaller vaccine doses of mpox vaccine administered in two doses, spread out over weeks to months, were similar to the full (subcutaneous) FDA-approved dose," said co-lead investigator and infectious disease specialist Angelica Cifuentes Kottkamp, from the varsity.

"Implementing the smaller dose was a good emergency measure in the face of immediate shortages of the vaccine," said Kottkamp, who is an assistant professor in the Department of Medicine at NYU Langone Health.

Further, the study also showed that those previously vaccinated against smallpox, as part of routine childhood vaccination programs, had a stronger immune response than those who had had no previous smallpox vaccination.

Levels of detectable IgG antibodies in blood samples were 2.7 times higher among those previously vaccinated against smallpox (and then additionally received the JYNNEOS vaccine) compared to those who were not dually vaccinated.

Because of their weakened immune systems, people living with HIV are particularly vulnerable to co-infection.

The study found no difference in the magnitude of the immune response between vaccinated people living with HIV (with immune CD4 cell counts above 200) and vaccinated people who are HIV-negative.