Ultimately the booster shots will be available to everyone, though those initially seeking a third shot will be the over-65s, border workers and medical staff - the first cohort to be vaccinated earlier this year.
Immunologist Graham Le Gros, who is director at the Malaghan Institute of Medical Research, said booster shots had great potential to change the game for the better.
"It seems that with this Pfizer vaccine, the third dose really lifts the level of immunity way beyond and it really gives the person who receives it a very strong immune response, very protective and it really resists against that waning immunity we've seen from overseas."
He said some people, such as those on immune suppressive drugs or those who are older, may not have had such a good immune response to two shots of the vaccine and the third dose, would bring their immune response up to a good level so they stay protected.
Le Gros said there was some speculation about how long the booster shot would last, but he was hopeful that it would give a couple of years of "durable immunity" because of the way that the immune system works.
"You change the cells of the immune system when you give that booster shot and actually these memory cells which long live, they go around different parts of your body and they stay there just waiting, waiting for the virus to come and actually that's the strength to the long-term immunity and it seems as though the booster shot will give those."
It was known from other vaccines that once those cells have been produced, they last for a long time, he said.
The Pfizer booster shot seemed to cover the existing variants of Covid-19 and it was also possible to mix the Pfizer booster shot with another type of vaccine, such as AstraZeneca, he said.
"So we're in a very good place for the booster shot and remember, think of winter next year, next year we're going to go into a situation where influenza could be around, Covid-19 will certainly be around as we go back indoors, so having a booster shot from now until autumn next year probably very good for people."
He said a clinical trial was under way in the UK comparing the Pfizer and AstraZeneca vaccines which would inform future decisions on what was a good combination of vaccines for the future.
"So remember this Covid-19 is going to be around for years to come, so we're going to have to work out which strategies to give booster shots and long durable immunity.
"I'm afraid it's bad news for everyone and they all go depressed but the virus is here and we've got to work with it and get rid of it."
Work was under way to make a domestically-produced booster shot, Le Gros said.
"Right now for New Zealand if you really want to increase your immunity, if you've actually been a bit immune-suppressed or you're over 65 where you've got a kind of hard old immune system, a booster shot is a very good thing to do to make sure that you're protected."
He said those who had their two shots over six months ago needed to ensure they achieved strong immunity by getting a booster shot.
