Jab targets, better mask wearing and tougher contact tracing key to COVID plan’s success

Today at national cabinet a phased plan out of COVID-19 was laid out. Great.

There is much to like about it. It gives hope. It emphasises and gives incentives for getting vaccinated.

There are four phases. The one we are in now, where everything is about vaccinating as many people as possible. Second, borders are opened to both vaccinated and unvaccinated travellers without quarantine. Third, we manage endemic COVID-19 infection in the community like other infectious diseases, such as influenza. Fourth, we get back to pre-COVID ways of living.

Underpinning these will be vaccination targets to transition from phase one to two. And a trial of home quarantine – for seven days – for vaccinated arrivals.

However, there are also some kickers in there – even naive statements. The most important one is the (now) overly strong focus on vaccination alone. Getting through the pandemic needs vaccination, but vaccination alone is not sufficient.

What am I getting at here?

Delta is super infectious - a reproductive rate of five or more. That means 80 per cent of the population need to be immune for the virus to not be able to spread easily. But vaccines are not perfect at stopping any risk of infection. I calculated that you need at least 90 per cent of the population (including children) vaccinated to get 80 per cent immunity.

“Our task is to pull the reproductive rate of Delta of five in a world with no COVID-19 control measures, down to an effective reproductive rate less than one.”

Professor Tony Blakely

Unfortunately, we are not going to achieve 90 per cent vaccination coverage across the whole population.

So, if we throw the doors open to the world at say 70 per cent vaccination coverage of just adults, with no ongoing other pandemic control measures such as aggressive contact tracing, mask wearing and physical distancing, it is going to be very ugly. Lots of natural infection, and high morbidity and mortality.

But there is another way, hinted at above. Do not focus just on a vaccination target, but the combination of measures we need before opening up. If we want to open up at low vaccination coverage, we will need to complement it with aggressive contact tracing and wide mask wearing.

The corollary of this is if we are sick of wearing masks, we would want the vaccination coverage to be higher before we open-up.

Credit:

Our task is to pull the reproductive rate of Delta of five in a world with no COVID-19 control measures, down to an effective reproductive rate less than one. There are many combinations of vaccination coverage, mask-wearing rules and contact-tracing intensity (with QR codes) that can achieve this threshold. But it is not a vaccination target in isolation.

Last quibble. It is a very brave politician or Prime Minister who declares “we will not use lockdowns again”. Witness Modi, witness Berejiklian.

Lockdowns, just like going to the dentist, are an unfortunate reality in these times. We will need them from time to time. Yes, the probability of needing them goes down enormously with high vaccination coverage (supported by other measures). But when we open the borders, there are likely to be pockets of outbreaks that may need localised stay-at-home orders.

I hope not, but everyone needs to know that this measure still stays in the toolkit in case we need it.

Otherwise, well done national cabinet. The week is ending better than it began.

Professor Tony Blakely is an epidemiologist and public health medicine specialist at the University of Melbourne.

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