By RNZ

Former chief science adviser Sir Peter Gluckman says the speed of contact tracing is critical to the success of fighting Covid-19.

Testing criteria for Covid-19 has been broadened which is likely to lead to an increase in confirmed cases and a corresponding need to trace more contacts of those who have the virus.

Research from Oxford University suggests the faster contacts of positive cases can be notified, the greater the hope of fighting the pandemic - and apps could be used to do that.

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The Oxford researchers wrote in Science magazine that the viral spread was too fast to be contained by manual contact tracing, but could be controlled if the process was "faster, more efficient and happened at scale".

Elijah Ross-Rutter said goodbye to his mother, who died of coronavirus, over a walkie-talkie. Video / CNN

"What's now been shown quite clearly by the Oxford group is that the most important and the most effective thing if you want to get out of lockdown is to rapidly contact-trace literally within hours of a diagnosis of a new person with the disease and work back to what contacts they have," Gluckman said.

An increasing amount of research was showing about 50 percent of transmission occurred before the individual was symptomatic, he said.

"Obviously, the longer a person is wandering around potentially spreading the virus ... the more people they are potentially going to infect.

"The more people we infect the more likely we are to not get the pandemic under control."

Gluckman said there are examples of apps being used to trace contacts in a way that maintained privacy. In South Korea the apps are used to message people to say they are contacts and should self-quarantine.

Watch: Samuel L Jackson shares hilarious advice to fight coronavirus. Video / YouTube

"While we're living with this high-trust model that we all agree is the best way of proceeding one needs to only inform and ask people who have been contacts to go into quarantine, into self-isolation, and be followed up."

Not everyone would download an app but even partial use could make a major difference to the contact-tracing load and the likely spread of the virus, he said.

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"New Zealanders by and large are trying to do their best and not everybody will be comfortable but sufficient numbers will be that this kind of technology will make a huge difference."

The priority now was to work out how to move out of the level 4 lockdown.

"As long as people comply with the social distancing and and self-isolation we're keeping it under some sort of control.

US president Donald Trump 'you don't know what the numbers in China are'. Trump added he is due to speak with Chinese leader Xi Jinping. Video / Guardian News

"But we can't stay on lockdown forever and we need to be thinking now, how we move out of it in a way that maintains the advantage New Zealand has.

"We have a burden of disease which our health system can cope with and that's what we've got to sustain.

"Elimination will take time. But we must have a burden of disease that we can sustain without overloading our healthcare system. And that's critical."

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Gluckman said masks had some value in reminding people of the pandemic and may reduce spread of droplets as the weather cools but may also lead people to become more complacent.