European countries could stretch out limited supplies of the monkeypox vaccine by administering smaller doses of the shot, the European Medicines Agency (EMA) said on Friday.
The agency's advice is in line with the so-called fractional dosing approach endorsed by U.S. regulators in which one vial of the vaccine can be used to administer up to five separate doses - instead of a single dose - by injecting a smaller amount in between layers of the skin (intradermal injection).
The vaccine - called Jynneos, Imvanex and Imvamune, depending on geography - was designed to be injected into a layer of fat beneath the skin, known as a subcutaneous injection.
As a temporary measure, national authorities may decide to use the vaccine as an intradermal injection at a lower dose to protect at-risk individuals during the current monkeypox outbreak while supply of the vaccine remains limited, the EMA said.
The recommendation is based on a study involving about 500 adults, which compared the performance of the vaccine given either intradermally or subcutaneously, as two doses given about a month apart.
Those who received the intradermal injection received one fifth of the subcutaneous dose, but produced similar levels of antibodies as those who received the original subcutaneous dose, the EMA said.
However, the agency cautioned there was a higher risk of local reactions, such as redness, and thickening or discoloration of the skin after intradermal injections.
More than 40,000 confirmed cases of monkeypox - including a handful of deaths - in over 80 countries where the virus is not endemic have been reported since early May.
The World Health Organization has declared the outbreak a global health emergency. The vaccine, made by Bavarian Nordic, is in short supply.
Several countries are stretching out the available doses, with unknown outcomes, to make the most of existing supplies.
Britain, Canada, and Germany are administering one dose per person instead of two, which allows them to inoculate more people even if they each may receive less or less durable protection.