By Stephen Wright

WELLINGTON, New Zealand--The task force developing a plan for quarantine-free travel between Australia and New Zealand is on track to give its recommendations to the two governments by early June, one of its coordinators said.

Australia and New Zealand, which have so far both contained the spread of the coronavirus, started working on the proposed travel "bubble" in early May, but it remains unclear how quickly the governments will be able to implement it.

New Zealand set a goal of eliminating the virus, though there has been confusion about its definition of elimination, while Australia has only discussed elimination as an option. Experts say about a month of zero new cases is needed to be confident the virus has effectively died out.

Scott Tasker, an Auckland International Airport executive who is joint chairperson of the working group developing the travel plans, said both countries would need to have high confidence that community transmission of the virus is not occurring in either nation.

Some 45 health experts and airline, airport and border-agency representatives working on the travel bubble aim to give their recommendations to the New Zealand and Australian governments by the second week of June, Mr. Tasker said.

"Mutual trust and recognition of each of these countries' reporting systems, their ability to track cases and their management of cases are the bedrock of getting travel open between the two countries," he said in an interview.

To further reduce risk, Mr. Tasker said the group is developing a "sensible set of measures" for travelers that would apply pre-travel, at the airport, on the plane, on arrival and at the destination. He declined to give specifics.

Before the outbreak, movement between Australia and New Zealand was largely unrestricted, with citizens of each country entitled to live and work in the other.

Border closures have hammered tourism in both countries and resumption of travel across the Tasman Sea would be a welcome cushion for businesses that are also reeling from severe recessions brought on by lockdown measures.

New Zealand was the most popular overseas destination for Australians, accounting for 40% of all foreign tourists, while New Zealanders were the second-largest source of visitors to Australia, after China.

Travel within New Zealand has resumed but movement between states in Australia still faces restrictions. New Zealand Prime Minister Jacinda Ardern earlier this week backtracked on an insistence that movement be unrestricted within Australia before the travel bubble can come into effect.

Epidemiologists at New Zealand's University of Otago--who provided modeling of deaths that helped to convince Wellington to lockdown the country from late March--say it would take about a month of zero new coronavirus cases to have high confidence of "epidemic extinction."

At current levels of testing in New Zealand, it would take 27 to 33 days of no new detected cases to have 95% confidence of extinction and 37 to 44 days for 99% confidence, they said in research posted online on Monday.

The Ministry of Health needs to urgently provide an official definition of elimination and provide more detailed data about cases so progress toward elimination can be monitored, the five University of Otago researchers said.

Australian experts also say maintaining zero cases for two incubation periods of 14 days each is needed.

New Zealand has had only three new cases of the virus in the past two weeks. Australia, which has five times the population of New Zealand, reported 15 new cases on Tuesday.

Establishing travel between Australia and New Zealand would provide knowledge and experience that could be applied more widely though future setups with countries would look different, Mr. Tasker said.

"It's not impossible and things are moving quickly, but of course we need to move cautiously as well because New Zealand and Australia have made sacrifices for the results that we've had," he said. "But I think where the risks are acceptable and can be managed, we absolutely should get the aviation system and connectivity moving." 



  Write to Stephen Wright at stephen.wright@wsj.com