A look inside Shaun Hendy's COVID-19 modelling that influences Government decisions

Auckland University Professor Shaun Hendy has provided a look inside his COVID-19 modelling, showing how vaccine uptake could make the path to elimination shorter. 

But Prof Hendy also revealed that high rates of vaccination won't necessarily lead to herd immunity, and that measures such as mask wearing and social distancing will still be required to keep people safe. 

In a virtual presentation to Parliament's Health Select Committee on Wednesday, Prof Hendy showed a series of graphs, one showing how long the path to elimination COVID-19 would be, depending on vaccine uptake.

"Is it correct to read that the time to eliminate an outbreak roughly halves if we move from 30 to 50 percent vaccination?" asked National MP Chris Bishop. 

"I think that's a fair assessment," said Prof Hendy. "You generally expect something like that, I mean, rule of thumb is, as you increase your vaccination rates, the time to elimination will decrease."

A look inside Shaun Hendy's COVID-19 modelling that influences Government decisions
Photo credit: Facebook / Health Select Committee / Te Pūnaha Matatini

Prof Hendy presented another series of graphs, demonstrating how the team of researchers at Te Pūnaha Matatini estimate how many cases will emerge from an outbreak, and the virus reproduction number known as the 'R' value. 

'R' is essentially the number of people that one infected person will pass on a virus to, on average. Measles has an R number of 15 in populations without immunity. That means, on average, one person will spread measles to 15 others.

The original Wuhan strain of COVID-19 had an R value of 2 to 3 but Delta's R value is about 5 to 6, with some researchers suggesting it is even higher. 

A look inside Shaun Hendy's COVID-19 modelling that influences Government decisions
Photo credit: Facebook / Health Select Committee / Te Pūnaha Matatini

"We put a lot of work into trying to estimate the effect of the reproduction number. We think it's sitting at about .4, that's our median estimate at the moment. Obviously there's a range of uncertainty around that point, but .4 is actually extremely good," Prof Hendy said. 

"The March, April outbreak was about .35, so, level 4 is working almost as effectively as it did last year with the wild type variant.

"We're still forecasting around about 1000 cases in total, and we start to see the chance that we'll eliminate the virus in the coming weeks."

ACT leader David Seymour asked how effective vaccinations will be against the Delta outbreak and to what degree it could prevent us from having to go into lockdown in the future. 

"I think one of the things people are really hoping is that vaccination will remove the need for lockdowns, but it sounds from what you're saying that we might be discovering through this outbreak that actually lockdowns are more effective than vaccination," Seymour said. 

"You want to think of them together...  I wouldn't want to look at them independently in context. They work together," Prof Hendy replied. 

"This might become important if we're thinking about boosters, for example, and in the future, you want to keep those things together. However, in general, the higher vaccination coverage, then the more effective our system becomes. 

"That means that the duration of those lockdowns will be shorter. So, what we have learned from this outbreak... controls have been effective, supplemented with the vaccine levels we've had.

"In the future, we'd expect them to be more effective as vaccination levels rise."

Green MP Dr Elizabeth Kerekere asked a similar question about how effective vaccination will be against the need for lockdowns. 

"There is still considerable uncertainty around that, and vaccine development is ongoing, but I think the weight of evidence at the moment suggests that it's not possible with our current suite of vaccines that are available, and certainly the Pfizer vaccine, to achieve herd immunity," Prof Hendy said. 

"In theory it's possible if we had very, very high rates of vaccination in some optimistic scenarios, but if you switch to the pessimistic side of the evidence and the data, it says that even at 100 percent, you'd still have substantial outbreaks because of the lower vaccine effectiveness.

"So in terms of how we move to opening our border and dealing with cases coming in more frequently because of relaxed border controls or moving away from MIQ, you do need some other controls in place.

"You can achieve herd immunity with widespread mask use, with some forms of social distancing with rapid testing... You could talk about herd immunity, but not solely from the vaccine."