Plenty of work has gone into strengthening the health service in the Cook Islands.

The travel bubble between this country and the Cooks officially opens today. However, the first flights do not depart Auckland until tomorrow.

Pacific health expert Colin Tukuitonga visited a few months ago and saw some issues that needed to be addressed, such as contact tracing and testing.

He told Kate Hawkesby the capacity of the health service to respond to an outbreak could be an issue.

Tukuitonga says Rarotonga is really really small, so being able to respond promptly and to contain the virus, will be the main challenge.

Tukuitonga visited a few months ago and saw some issues that needed to be addressed -- such as contact tracing and testing.

He says at the time he suggested people get the jab before the border opens.

"Obviously they've gone and opened the border and the vaccination... is yet to roll out. I'm not sure why that happened, but I did suggest perhaps vaccinating people first."