"There is no evidence that either of these new variants causes more severe disease than the original.
"But, there is strong evidence that the B.1.1.7 variant spreads more easily from one person to another.
"This means that the number of new cases per infected person (the so-called R number) is 40-70 per cent higher than the original strain.
"This is a serious concern because of the potential for explosive exponential growth."
Plank said the higher infection rate raised the risk of the variant leaking through our border because there was a greater chance of a quarantine worker getting infected.
Consequently if there was a community outbreak, it would spread much faster and lead to much bigger outbreaks because it was compounded by exponential growth.
For example, the original strain of Covid-19 would typically infect about 160 cases after five links in the chain, whereas the new variant would typically infect about 1000 cases in the same time.
Plank said if there was a community outbreak, there could need to be stricter restrictions to bring it under control.
"All the tools we have developed to fight Covid-19 will still be effective, but we will need to use more of them.
"Alert level 3 was effective in containing the August outbreak, but it's likely we would need to use level 4 to have the same effect on the new variant.
"And restrictions might need to be in place for longer to eliminate the virus."
Plank said the Government's recently-announced additional day zero test on arrival and a pre-flight test for people departing from the United States or the UK were good ideas.
However Plank said it would be sensible to extend these requirements to all arrivals as the strain was spreading around the world rapidly.
A period of pre-travel quarantine would also help to reduce the number of cases arriving at the border, he said.
While there was no evidence existing vaccines were any less effective against the new a higher proportion of New Zealanders would need to be vaccinated to achieve immunity due to the increased transmission rate.
On Sunday epidemiologist Dr Michael Baker said other measures to restrict the chances of an outbreak of the new strain could involve a "traffic light system" for travel.
Countries with no or low community transmission could be green, while places like the UK and parts of the United States would be red, meaning flights from there would be suspended.
Canada had banned flights from the UK since December 21 to keep out the new strain.
France, Germany, Italy, the Netherlands, Belgium, Austria, Ireland and Bulgaria all announced restrictions on UK travel.
In response to the new strain, the Iwi Chairs Forum Pandemic Response Group has issued a range of priorities to protect vulnerable groups of people.
Various studies have found Māori would be disproportionately impacted by Covid-19 were there to be a large outbreak here, largely due to pre-existing health inequities.
The latest research found Māori and Pacific people were more than twice as likely to be hospitalised for Covid-19, findings that prompted a call to officials currently prioritising vaccine shots.
Dr Rawiri Taonui, who conducted research for the Iwi Chairs Forum, called for more urgency in Government response, including applying the pre-departure negative test to all travellers as soon as possible, and bringing vaccination rollout forward to February.
Due to the disproportionate effects on Māori, Taonui said the "at-risk" age for Māori should be lowered to 50.
He also said the Government needed to consider capping arrivals at 300 per day, down from about 400 currently, and when the number of active cases in MIQ reached 20 to 30 cases, cap the number of entries to a lower level.
"With the threat from new strains the number of arrivals into New Zealand is no longer sustainable."
