Saturday, November 27

Elimination possible in the coming weeks: Covid-19 model, Shaun Hendy


Te Pūnaha Matatini Covid-19 data modeling expert Shaun Hendy says Alert Level 4 in Auckland is working almost as well against Delta as the lockdown as it did last year.

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Covid-19 Modeler Shaun Hendy
Photo: Shaun hendy

He was explaining some of the different models that were used to estimate things like population immunity thresholds and virus spread to the Health Selection Committee this morning, and said the estimated effective reproduction, or R, for the current outbreak it was now about 0.4.

“That is our median estimate at the moment, obviously there is a range of uncertainty about it, 0.4 is really extremely good. The outbreak from March to April was about 0.35, so alert level 4 in Auckland is working almost as well. effectively like last year. “

Prof Hendy said that reaching an elimination stage, where the virus is no longer circulating in the community, will soon be possible if restrictions continue in Auckland.

“We are still forecasting around 1000 cases in total, and we are beginning to see the possibility that we will eliminate the virus in the next few weeks, assuming we remain at alert level 4.”

“You might be remembered in the media saying ‘I’m a little anxious about level 4 and we may need to strengthen it because of Delta … what we have learned I think in this outbreak is actually our alert level 4 setting. effective and even though we are sitting on the outer edges of this, we are seeing elimination. “

He said it was difficult to estimate how New Zealand would have fared without the lockdown, but it seemed likely that medical care would have been at full capacity this week.

The model estimated that the time to elimination could be reduced by about half by increasing vaccination levels for 30 to 50 percent of the population.

“As vaccination rates increase, the elimination time begins to decrease.”

He said it was important not to consider current vaccination coverage regardless of the effectiveness of the current lockdown on the spread of the virus.

“When we’ve looked at how well alert level 4 has worked, we’ve done it in the presence of the vaccine coverage we’ve had, so I wouldn’t want to see those two things independently.”

“In general, however, the higher our vaccination coverage, the more effective our alert level system will be.”

However, it was almost impossible to achieve herd immunity through vaccines alone.

“In theory, it is possible if we achieve very high vaccination rates in some optimistic scenarios, but if you switch to the pessimistic side of the evidence and data, then it says that even at 100 percent [vaccinated] it would still have substantial outbreaks due to the effectiveness of the vaccine.

“There is still considerable uncertainty around that and vaccine development is ongoing, but I think the weight of evidence at this point suggests that it is not possible with our current set of vaccines that are available … to achieve immunity. collective “.

However, including other measures could also do this.

“It is necessary that other controls be implemented, and with those other controls you can achieve group immunity, so with the widespread use of masks, with some forms of social distancing, with rapid tests, one could speak of group immunity, but not only the vaccine.

“So I think it’s also important to point out that some of those things also require compliance.”

He said that Delta was very difficult to deal with, especially in workplaces and educational settings.

Understanding of the risks had improved a lot, but some changes could be made based on the science of aerosol transmission risk, compared to airborne and surface transmission, he said.

“I have ongoing concerns and I think we need to keep looking at the science, as well as what is reasonably feasible to do indoors.

“We have not designed our interior spaces to be … resistant to respiratory viruses and there is much more we could do there. I think we have to make better use of the use of masks; we tend to encourage the use of masks in lower areas. hazardous environments and we do not necessarily require the use of masks in those high-risk environments which are workplaces and educational settings.

“I’d like to see faster testing, I mean, I think it’s a tool that we haven’t taken advantage of and I think we’ll have to … that could make a significant difference.”

He said that anyway, the more people tested, the more confidence it would give authorities that the virus was being eradicated.

“It is difficult for us to give a kind of difficult number. I guess I would like to see about 10,000 tests a day for the next two weeks.”

Hendy said rapid antigen tests could be extremely helpful next year as the country begins to move toward greater vaccination coverage and a strategy that can accept a higher level of risk of infected people entering the country.

“Rapid antigen tests are not as sensitive as PCR tests … they are not as good at detecting cases at the end of the article, but the fact is, because you can get those response times much faster, they can be really useful. “

He said speed also meant that, for example, they could be more effective for pre-start tests.

“Also, because you can test more frequently, you can more than compensate for some of the sensitivity deficiencies with daily testing.”


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