Parents hoping to have their children vaccinated privately against meningitis B have been told there is a shortage of vaccine.
The NHS programme to vaccinate babies against the deadly bug is unaffected by the global shortage of Bexsero.
But private clinics in the UK have been advising parents that they cannot start any new courses of the vaccine.
Any child who has had one dose already should, however, be able to receive follow up doses to finish the course.
A statement from manufacturer GlaxoSmithKline (GSK) said: "Due to unexpected global demand for Bexsero during 2015, we are experiencing supply constraints during the first half of this year.
"Although vaccination through the NHS childhood programme has been prioritised and is unaffected, we have unfortunately had to ask private clinics temporarily to not start new courses of vaccination.
"Children who have already started their course of the vaccine privately should still be able to receive their follow up doses.
"We know the unexpectedly high demand for the vaccine reflects the importance parents have placed on protecting their children from meningitis B, so we are working hard to increase supply, and expect to have increased stock by summer 2016."
Dr Mary Ramsay, head of immunisations at Public Health England, said: "We are aware that GSK has supply constraints on the Bexsero vaccine for the private market.
"However, this does not impact the NHS programme and the meningitis B vaccination programme will continue to be delivered to eligible infants as part of the NHS childhood immunisation schedule.
"If we become aware of issues affecting the supply for the NHS immunisation programme, we will inform healthcare professionals and parents."
Meningitis B was added to the NHS childhood immunisation programme in September.