The AstraZeneca vaccine is available for Kiwis over the age of 18 from today

One-hundred-thousand doses of AstraZeneca arrived from Australia last week - enough for 50-thousand people.

It offers an option for those with medical reasons not to have the Pfizer jab.

The Immunisation Advisory Centre's Director says both vaccines perform very well - but are very different.

Nikki Turner says Pfizer is an mRNA vaccine, and codes our cells to make protein that will trigger an immunise response.

She says AstraZeneca is a vector vaccine - where a genetic piece of material is inserted into an inactivated virus.

Pfizer booster shots for fully-vaccinated people can also be booked from today.