There will be delays with the supply of a new flu jab for over-65s this year, the chief medical officer has said.
Dr Michael McBride said that "manufacturing constraints" would mean that, for some people, the jab will not be available until late November.
However, he added that everyone eligible would receive their injection before the "peak season" for the virus.
Dr McBride said almost a third of those who could have taken the jab last year did not do so.
"Because flu viruses change continuously, we have also invested heavily in this year's flu programme, introducing two new vaccines to offer event great protection to those most at risk," Dr McBride wrote in The Belfast Telegraph.
"Due to manufacturing constraints, Flaud is being distributed on a staggered basis across the UK.
"Everyone eligible here will be able to get it by the end of November, well in advance of the traditional flu season.
"While this might be a bit longer than previous years, there are very strong grounds for believing it is worth it," he added.
The chief medical officer urged all those eligible to get the vaccine, emphasising that last year saw "one of the worst flu seasons in Northern Ireland".
He said: "119 people were critically ill and needed intensive care and 22 of those people died."
Out of almost 890,000 people eligible, 330,000 did not not get their flu vaccine in 2017.
Two GP practices in County Antrim have told patients that they were experiencing a shortage in supplies.
Ballymoney Family Practice has had to postpone appointments until late November, while Randalstown Medical Practice was forced to operate on a first-come, first-served basis for patients up to the age of 74 on Wednesday.