WELLINGTON, Aug 11 (Reuters) - New Zealand should keep its borders shut until early 2022 and reopen only after the vast majority of its adults have been vaccinated against the coronavirus, a government-appointed panel said on Wednesday. It said the country, which last reported a local case of COVID-19 transmission in February, needs to stick to its strategy of eliminating the virus to avoid straining its health system, with the virus rapidly mutating overseas. "The advisory group considers that an elimination strategy is not only viable, but also the best option at this stage of the pandemic," the panel said in a report. New Zealand Prime Minister Jacinda Ardern has won global plaudits for containing local transmission of COVID-19 through tough lockdowns and shutting the border in March 2020. The country has recorded just 2,500 cases and 26 deaths. The government is set to announce plans this week for reopening, based on the experts" advice. "The challenge of dealing with regular importations of the virus through our borders should not be underestimated," the panel said in a report. "Hence we support the idea that re-opening of the borders in 2022 should start in a carefully planned, phased way..." The panel recommended New Zealand"s vaccination programme should be completed before reopening. So far only 21% of the country has been fully vaccinated. "We need to do more to further strengthen our borders and bolster our health defences, including through the vaccine rollout, before we can safely open the border further, and that will take a little more time to properly prepare," Associate Minister of Health Ayesha Verrall said in a statement. She said the panel"s advice had evolved due to the emergence of the highly infectious Delta variant. Businesses and public sectors facing worker shortages have called for a more rapid opening up, but the panel said that would make the country vulnerable to infection. read more Ardern last week opened one-way quarantine-free travel for seasonal workers from Samoa, Tonga and Vanuatu to address labour shortages in the horticulture industry. read more New Zealand suspended a quarantine-free travel "bubble" with Australia in July following outbreaks of the Delta variant there. read more