Covid-19

NZ scientists horrified at ‘herd immunity’ strategy

The idea of herd immunity and elderly people self-isolating for several months has been described as an experiment on a massive scale

While New Zealand’s borders close, the United Kingdom’s approach to Covid-19 has scientists horrified.

A strategy of herd immunity, coupled with isolation for vulnerable people, has been touted by the UK's chief scientific advisor and the health minister. 

The approach has led to Singapore adding the UK to a list of countries whose arrivals will receive a strict 14-day stay-at-home notice. One Singaporean official described the UK as having “abandoned any measure to constrain or restrain the virus”.

Unlike New Zealand, the United Kingdom has not put measures in place asking visitors to self-isolate.

Instead it appears there’s going to be a focus on keeping those most vulnerable to serious illness from the virus safe, while others are left to get sick. 

It’s reported people over 70 years old in the United Kingdom may be asked to self-isolate for “several months”. 

The UK’s potential self-isolation of over-70s comes after the UK’s chief scientific adviser Patrick Vallance suggested a 'herd immunity' approach. 

"Our aim is to try and reduce the peak, broaden the peak, not suppress it completely," he said.

It’s an idea that has drawn widespread condemnation. An open letter signed by more than 200 scientists calls for greater social distancing for all and says:  

“Going for 'herd immunity' at this point does not seem a viable option, as this will put NHS at an even stronger level of stress, risking many more lives than necessary."

Comments since Vallance’s suggestion including one from the Health Secretary Matt Hancock who said herd immunity isn’t a policy, have done little to reduce the horror at the idea, or the general confusion over U.K’s approach to the virus.

“When you have that proportion of the community affected, you can probably calculate how many people will be dead. When you have that overwhelming explosion of cases, your health system is overwhelmed and your mortality rate goes up.”

Herd immunity occurs when there are enough people in a population immune to a disease that it no longer circulates. Normally, this is done with vaccines, which give immunity without letting a person get sick.

There is no vaccine for Covid-19. To achieve herd immunity, a large number people would have to catch the virus and recover. If vulnerable people self-isolate, at some point, theoretically, they would be safe because the virus would no longer be spreading.

Vallance estimated around 60 percent of the UK’s population - roughly 40 million people - would need to catch the disease to achieve herd immunity. 

The suggestion of a herd immunity strategy for Covid-19 was met with horror by University of Auckland associate professor Helen Petousis-Harris.

“At what cost? Throwing people under the train? There are younger people getting seriously ill as well.”

The idea raised ethical concerns. 

“When you have that proportion of the community affected, you can probably calculate how many people will be dead. When you have that overwhelming explosion of cases, your health system is overwhelmed and your mortality rate goes up.”

Based on population statistics from the 2018 Census, the 60 percent figure would mean nearly 2.9 million New Zealanders would need to get Covid-19 to achieve herd immunity. 

The fatality rate calculated by the Chinese CDC for those aged between 10 and 40 is 0.2 percent. It gradually increases from there. If you’re aged 40 to 49 there’s a 0.4 percent of dying, 50 to 59-year-olds have a 1.3 percent chance of dying. If you’re aged 60 to 69, you have a 3.6 percent chance of dying.

Back-of-the-envelope calculations can give a rough idea of likely deaths. If 60 percent of New Zealanders aged 60 to 69 caught Covid-19, 345,114 people would be infected. Based on the fatality rate of 3.6 percent, 12,424 people in that age group alone would die.

If there was no isolation of vulnerable elderly, the overall fatality rate would sit at around 3.4 percent. The total deaths in New Zealand would be close to 97,800.

Actual fatality rates are likely to vary by country and will depend on the ability of the country’s health system to cope with cases. Newsroom reported today New Zealand has 176 ICU beds.

University of Auckland microbiologist Siouxsie Wiles is also horrified at the thought of attempting herd immunity without a vaccine. 

“I thought it was satire at first, I thought it was a joke.”

There’s no knowledge about whether herd immunity through prior infection is possible - or how long it might last.

“I'm horrified. Absolutely horrified. And I know that many people like me are. This is an experiment and we're just flabbergasted that you would do an experiment on this scale.”

Self-isolation for over 70s

UK Health Secretary Hancock said emergency powers including self-isolation will be announced Tuesday, but wouldn’t give details on when the call would be made, or how it would be managed.

At the time of writing, there are 1144 confirmed cases of Covid-19 in the UK. Confirmed cases in New Zealand are currently at eight and so far there has been no community spread.

If New Zealand were to take the same approach the UK is proposing, based on 2018 Census numbers, around 498,200 people would need to self-isolate.

Elderly people with the virus have a higher mortality rate than younger people. The rates calculated by the Chinese CDC estimate 8 percent of those aged 70-79 die from Covid-19. For those 80 and over the rate is 14.8 percent.

The Ministry of Health has been asked if this has been considered as an option in New Zealand, and what might be a trigger point to make the decision. Due to the number of queries it's currently responding to, it was unable to reply at the time of publishing. 

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