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Dwindling numbers of community Covid-19 cases - 55 yesterday and 39 on Saturday, a welcome drop from a recent run of triple digit case numbers - suggested the current Delta outbreak could be coming under control, the University of Otago academic said.
However, the detection of five further cases of Omicron at the border yesterday showed the scale of the future threat New Zealand faced, Prof Baker said.
"For a virus only one thing matters and that is reproducing itself ... this is survival of the fittest in front of our eyes.
"Delta went from just a few cases to taking over the world, and Omicron is likely to do the same thing."
Director-general of health Ashley Bloomfield last week said the Government was committed to keeping Omicron out of the community for as long as possible and that was absolutely the right approach, Prof Baker said.
"We need to respond to Delta, the threat in front of us, but the Government also needs a proactive plan to deal with Omicron which should include reviewing all our border settings and MIQ to make sure we are closing off any loopholes that the virus could exploit.
"We need to get as many boosters into people as we can but even before that we need to focus on keeping it out and maybe deferring any plans to reopen the international border."
A Ministry of Health spokesman yesterday said all arrivals at the border would be managed cautiously.
"New precautions set out that whole genome sequencing on all new border cases of Covid-19 is undertaken rapidly to identify any new cases of the Omicron variant.
"These measures also see all passengers on flights with Omicron cases being required to complete all 10 days at a managed isolation facility, rather than spending the last three days ... in self-isolation."
Omicron was first registered weeks ago, but it is sweeping across the world.
Far more transmissible than Delta, British modellers have estimated Omicron could daily hospitalise thousands and overwhelm the UK health system.
They urged the British Government to reintroduce stringent Covid-19 protection measures. Some countries have already taken that step, notably the locked-down Netherlands.
Prof Baker said New Zealand did not have that yet and people should still be able to enjoy their Christmas break. The panic in Europe showed the havoc Omicron could wreak if it got loose here.
"People should be able to relax, but ... take all the precautions."
Prof Baker said it was good the daily rolling average of cases was falling, although the full impact of lifting domestic travel curbs last week was yet to be factored in.
"The fact the reproduction rate of the virus has been pushed down below 1 suggests that the various countermeasures are having an effect."
Yesterday, there were 56 people in hospital with Covid-19. Cases in hospital: 51 across Auckland, 2 in Waikato and three in Tauranga.
More than 18,000 tests were carried out and there 1902 active community cases in total.
More than 15,000 vaccinations were administered: 1728 first doses, 6630 second doses, 191 third primary doses and 6916 booster doses.