A new model has suggested how so-called "super-spreaders" could be targeted for a Covid-19 vaccine - but Kiwi experts question whether that'd be needed in coronavirus-free New Zealand.
A team of Australian scientists have developed a theoretical model for a new vaccination strategy that would have the biggest impact — with the least amount of resources — on suppressing the spread of the coronavirus.
That's based on pin-pointing locations visited by people most likely to become superspreaders, and vaccinating them.
The research team used anonymised location data for the movements of 600,000 people in Shanghai and Beijing who were on a messaging app called Momo.
The team analysed a staggering 56 million location visits in just 71 days.
"Focusing on the locations where a potential superspreader visits and vaccinating all direct and indirect contacts in the cluster at those locations is the most effective method," said Professor Bernard Mans, of Macquarie University's Department of Computing.
"We found this approach would be as good as vaccinating identified superspreaders based on an accurate contact list, and significantly better than random vaccinations."
A superspreader is someone who transmits an infectious disease to an unexpectedly large number of other people.
The researchers then calculated all the other people they would have come in direct and indirect contact with and then extrapolated these trends to develop a model to test the theoretical effectiveness of a vaccine strategy.
Using the location data, they ranked people into six classes by the number of places they'd visited — the higher the number the more contacts.
For example, Class 1 meant the person had only stayed at home or visited local shops and been in contact with up to five people.
A person in Class 2 would have also gone to a coffee shop or a bus stop and been in direct and indirect contact with up to 15 people.
A Class 3 person would have gone to a local train station or the office, a small park or a swimming pool and been in close proximity to up to 25 people, whereas a Class 6 person had visited highly populated public places like universities, airports and stadiums and potentially been in direct and indirect contact with more than 100 people.
The Class 6 people are clearly more likely to become superspreaders.
"Our research shows that to be effective, it's not about who exactly a superspreader has been in contact with 24-7 but where they've been that should be the focus of vaccination," Mans said.
Past research has shown for privacy reasons, people often won't reveal all their contacts or they forget all the people who they've met — so it was unreliable.
Mans pointed out that until now, current theoretical vaccination strategies were not designed to capture indirect transmissions and potentially miss out on individuals' numerous indirect links, such as people who get into a lift after them.
Focusing on location means you can easily discover indirect as well as direct contacts.
But Professor Michael Plank, a University of Canterbury mathematician and Covid-19 modeller with Te Punaha Matatini, questioned how such a system could be implemented without accessing people's private information.
"You'd need to think about privacy issues and the practicality of identifying these people, and how realistic it'd actually be to put this into practice."
Even if a voluntary approach targeting superspreaders was tried, he said, it could incentivise people to meet the criteria - or not to, if they opposed vaccines - which made the concept tricky.
Otago University epidemiologist Professor Michael Baker also saw some clear issues.
"A lot of work has done here to identify which categories of people are most important, and how to reach those categories with vaccination," Baker said.
"But it's a whole other level to say that, we're going to identify specific individuals."
In any case, Baker felt the strategy wasn't so relevant to a country like New Zealand, which has eliminated the virus from the community, and more applicable to regions like the US and Europe, where there was widespread transmission.
"Those countries are in a race against time to try to protect those that are most vulnerable, but here, we could take another approach, because the drivers really are quite different."
Research, Science and Innovation Minister Megan Woods has signalled vulnerable people and frontline Covid-19 workers - including border and healthcare staff - will likely be the first to receive a vaccine when it becomes available.
People more susceptible to Covid-19 include older communities as well as Māori and Pasifika.
The Health Ministry was still working through the details, but there would be three priority groups: those at risk of spreading Covid, those at risk of contracting Covid, and those with increased risk of increased mortality and morbidity with Covid.
New Zealand will be receiving 1.5 million doses under its first vaccine pre-purchase deal - enough to immunise 750,000 people - and agreements with other vaccine makers are expected to be announced before Christmas.