New Brunswick parents are being warned that a shortage in H1N1 vaccine may delay the planned second shots for their children. (CBC)

New Brunswick's chief medical officer of health is cautioning parents that any children who have received their first H1N1 shot may not be getting their booster after 21 days.

Dr. Eilish Cleary said on Thursday that those second vaccinations will likely be delayed due to the shortage in swine flu vaccine. The delay will also allow the province to focus on other groups that need to be vaccinated.

Children who were in the early vaccination groups received a half dose and were told to return for a second shot in three weeks.

Cleary said the delays shouldn't be a problem for the children.

"We are saying that parents who have a child due for a second shot not to worry next week. We say a minimum of three weeks apart or 21 days apart," Cleary said.

"But it can be four, six, eight weeks, 10 weeks apart, it doesn't have to be right on the nose of three weeks."

On Thursday, federal health officials said healthy children between three and nine may only need to receive one shot of the H1N1 vaccine.

The Public Health Agency of Canada has released clinical trial results from Europe that show a half dose of vaccine or a booster will give protection from swine flu but only for healthy children over three years of age.

Federal officials released three new dosing recommendations:

• Healthy children between three and nine years of age should only receive a single half-dose of the H1N1 vaccine, and they do not need to return for a second vaccine for now. This recommendation may be updated as more information becomes available.
• Children between six months of age and three years old should receive two half-doses of adjuvanted H1N1 flu vaccine, given at least 21 days apart. This guideline is unchanged.
• Children with chronic health conditions between three and nine years of age should receive their first half-dose of the pandemic vaccine as soon as possible. They should also receive a second half-dose at least 21 days later.