ROTTERDAM - The monkeypox vaccine that is become the main method doctors are using to try to stop the global scourge may be less potent than hoped, new research shows.

The recommended series of shots with Bavarian Nordic's Jynneos vaccine yielded relatively low levels of monkeypox antibodies with poor neutralising capacity, said esearchers at the Erasmus University Medical Centre in Rotterdam, Netherlands.

Those immunised had not been previously infected or vaccinated against smallpox, which is believed to provide some protection against monkeypox. Neutralising antibodies have become part of the common lexicon during the Covid-19 era, thanks to their ability to bind to the coronavirus and stop it from entering healthy cells.

Although these proteins are almost certainly needed to prevent a monkeypox infection and the rash it causes, scientists do not know yet what levels are required to confer protection.

"The level of optimism for the vaccine far exceeds the data currently available," said Dr Helen Petousis-Harris, a vaccinologist at the University of Auckland, who was not involved in the research.

"There are a lot of information gaps and we have to be cautious as it gets rolled out, especially to avoid vaccinated people having a false sense of security."

Protection question

The finding of lower-than-expected levels of neutralising antibodies raises questions about how well vaccinated individuals are protected, wrote Erasmus scientists Marion Koopmans, Rory de Vries and their co-authors in the paper that was released on Thursday ahead of peer review.

"Studies following vaccinated individuals are necessary to further assess vaccine efficacy," they said. Representatives for Bavarian Nordic did not immediately respond to requests for comment made after hours.

The authorities in more than 70 countries are seeking supplies of the Danish company's vaccine, also sold as Imvamune in Canada and Imvanex in Europe, to thwart the global spread of monkeypox.

It has infected more than 50,000 people since a flare-up of the disease was reported in Britain in early May.

While some scientists are testing dose-sparing approaches to stretch limited supplies of the immunisation, the Erasmus work found dose sparing "has a negative effect" on vaccination. A third dose boosts the antibody response, as does immunising individuals who were vaccinated against smallpox decades earlier, they found.

Monkeypox is closely related to variola, the virus which causes smallpox - the first human disease to be eradicated.

The Bavarian Nordic vaccine is deemed a safer immunisation than the one that wiped out smallpox as it uses a weakened, non-replicating version of a related virus. Efficacy data on its use against monkeypox in humans is lacking, the Erasmus scientists said.

Experiments in animals showed it generated both antibodies and T-cells against monkeypox, but not enough to prevent infection or the emergence of some skin lesions. BLOOMBERG