Delta presents a substantially more challenging foe to eliminate. The experiences of other jurisdictions offer examples we can learn from, writes epidemiologist Jennifer Summers.
The delta variant has been called a game-changer, and in a lot of ways it is. Vaccines may be less effective against this variant of Covid-19 and delta is much more infectious than other forms of Covid-19 we have experienced in New Zealand. We need to use all the tools in New Zealand’s arsenal to combat delta. One of the best ways of doing this is by looking into how other jurisdictions are responding to delta.
Why are we so worried about delta?
Delta originated in India in October 2020 and in that time has become the most dominant strain of SARS-CoV-2, the virus that causes Covid-19. delta produces a higher viral load in the lungs of those infected, meaning that there are more viral particles inside the person infected with this variant. This results in delta having both a shorter incubation period and being more infectious than other variants. delta is also causing more serious illness with increased risk of hospitalisation. The further worry with delta is that it appears to be more resistant to vaccines, meaning that the vaccines are not quite as good at preventing infection and less effective in stopping transmission from a vaccinated person to someone else.
Epidemiologists often talk about reproduction number or R0, and this refers to how many people will be infected by each case. Delta has a R0 of 5-7, meaning a delta case will on average infect around 5 to 7 other people. To put this into perspective, delta has a higher reproduction number than many other viral infections such as influenza (Ro=1-3), Ebola (Ro=2) and the original strain of SARS-CoV-2 (R0=2.8). Nevertheless, it is not as high as chicken-pox (Ro=10-12) or measles (Ro=12-18). Given all these features of delta, New Zealand’s control of Covid-19 is being put to the test by our delta outbreak and this threatens our ability to continue with an “elimination strategy”.
What’s happening in Australia?
Australia is in the midst of its largest outbreak in the Covid-19 pandemic, largely fuelled by the delta outbreak in New South Wales. Even with various state border restrictions, this outbreak has spread into other Australian states/territories and also New Zealand. New South Wales officials initially decided against a strict lockdown within the greater Sydney region, and this has most likely resulted in the prolonged outbreak, with serious pressure put on Sydney’s health system.
Queenslanders have experienced a variety of snap lockdowns over the last several weeks as they respond to delta. Unlike NSW, the lockdowns in Queensland have been strict and imposed with short notice. For the last several weeks, Queensland has managed to keep the number of Covid-19 cases in the community to less than 10 per day. Queensland has recently begun building its own dedicated regional Covid-19 quarantine facility, much like the successful Howard Springs Facility in the Northern Territory.
South Australia has also managed to keep their Covid-19 cases low, with daily cases not reaching double-digits since June 2021. A state-wide snap lockdown in July keep the delta outbreak in the community from spreading widely. This lockdown was similar to New Zealand’s alert level four, with strict restrictions.
Western Australia and the Northern Territory have had few reports of recent community cases of Covid-19. While they have both experienced delta cases, they have both used various localised lockdowns to reduce transmission. The remaining state of Tasmania has the advantage of being an island and has managed to keep delta out of its population. However, officials are still aware of the risks posed by delta, and are planning for an outbreak scenario, known as the “Delta Shield’“. This would involve a snap lockdown and mandated public health measures such as restrictions on gatherings and mask use.
How is delta affecting other jurisdictions?
Taiwan is often used as a model example for its relatively successful response to the Covid-19 pandemic. However, in April 2021 Taiwan experienced its largest Covid-19 outbreak, involving multiple clusters connected to international flight crew and a quarantine facility in the capital city of Taipei. When the delta variant was found at the tail-end of this outbreak, Taiwanese officials used a localised lockdown to reduce transmission of the virus, rather than a nationwide lockdown (which has never been used in Taiwan). The Taiwanese are now reporting zero cases of Covid-19 in the community.
When we look at other jurisdictions in Asia, we can see that there are a wide range of successes and failures when dealing with delta outbreaks. For example, Malaysia, Japan, South Korea and Vietnam are all experiencing record numbers of Covid-19 cases, largely driven by delta. Whereas recent outbreaks largely fuelled by delta are being quelled in Singapore (soon to be moving away from a “zero-tolerance“ approach to Covid-19) and China (using a mixture of localised lockdowns/restrictions and mass testing). Like New Zealand, Hong Kong uses an elimination strategy, and so far has not had a delta outbreak. Any reports of Covid-19 cases swiftly results in localised lockdowns and tight restrictions.
Looking elsewhere, Iceland has one of the highest Covid-19 vaccination rates in the world, with around 84% of the eligible population fully vaccinated (much higher than the rate of about 30% in New Zealand). However, like Australia, Iceland is now experiencing its largest Covid-19 outbreak, caused by delta. Many of the recent cases are occurring amongst the fully vaccinated, in what is known as breakthrough infections. Breakthrough infections are also driving the large delta outbreak in highly vaccinated Israel.
What does this mean for New Zealand?
New Zealand is one of a number of nations still using a Covid-19 elimination strategy. However, delta has made this much more difficult to follow. It is clear from other nations that a swiftly executed lockdown (whether localised or nationwide) can be effective in dealing with delta outbreaks along with other public health measures, such as physical distancing, vaccination and mass mask use. This is why our government quickly put New Zealand into a nationwide lockdown following the confirmation of just one community case in Auckland last month.
Current research suggests that being vaccinated can reduce the full impact of infection from delta, by reducing infections and serious complications. However, relying on high-vaccine uptake in the population is not enough to tackle delta, as both Iceland and Israel have shown.
New Zealand should consider new public health measures, such as having purpose-built quarantine facilities like Queensland and the Northern Territory. This will help reduce the risk of future MIQ failures. Other possible improvements to New Zealand’s defence against delta include tweaking our alert level system, mandating QR code scanning, increasing wastewater testing and improving ventilation management.
Delta is the biggest challenge to date for New Zealand maintaining its elimination approach. However, the benefits of elimination means New Zealand keeping cases and deaths relatively low. This is important given that the long-term effects of long Covid are still unknown and we want to protect tamariki who are largely unvaccinated. We want to avoid a health system overload (like in New South Wales) and prevent severe health inequities. We also want to protect New Zealand from new Covid-19 variants which may be worse than the delta variant.
The delta variant of Covid-19 will continue to be a challenge to New Zealand’s elimination strategy in the long-term, perhaps until even better vaccines become available. Fortunately, other jurisdictions show it is possible to control delta outbreaks and New Zealand still has a range of options for improving our response in the future.
Jennifer Summers is an epidemiologist at the Department of Public Health, University of Otago, Wellington. This piece is based on a post at the department’s Public Health Expert blog
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