Covid 19 Delta outbreak: Michael Baker on Delta being at 'peak fitness', fears for next variant

It's not so deadly that it kills most of its hosts before they can spread it to other people.

But it can be so sneaky and subtle, some people right now in Auckland probably have it without knowing.

For a brainless microscopic parasite, the Covid-19 Delta variant is doing quite a job of keeping thousands of the world's smartest humans busy.

It's a relentless contest, epidemiologist Professor Michael Baker said, and it's highly likely the next major step in virus evolution will involve a more vaccine-resistant variety.

For now, Delta had largely vanquished all other Covid-19 variants, and Baker said the strain was close to "peak fitness" for a virus.

"It's the only game in town," Baker told the Herald.

The variant had infected hundreds of millions of people worldwide, but could still evolve.

"The virus may still have potential to optimise its performance in some way," the University of Otago public health expert said.

"Now that much of the world's population is vaccinated, there'll be a question about whether a more resistant variant can take over."

The Delta variant is near the acme of its potential powers, but could yet evolve, said University of Otago epidemiologist Professor Michael Baker. Photo / Supplied

Despite Covid-19's ability to outmanoeuvre humanity, Baker said there was cause for optimism.

"At the moment the vaccine is getting in the way of [Delta] infecting people."

And thousands of scientists across the world every day were tracking Covid-19's latest moves.

"Everyone's very conscious of that, so that's why all around the world there's a huge amount of genetic sampling of the virus."

Baker said there was a strong argument for vaccinating as many people worldwide as possible to keep ahead of any vaccine-resistant mutant.

A study from Austria's Institute of Science and Technology (IST) in late July found rapid vaccine uptake decreased the chances of a resistant strain emerging.

But counter-intuitively, when restrictions were eased even in highly vaccinated countries, the chances of a new resistant strain increased, the IST study found.

Baker said a concerning scenario was emerging in the UK. Despite high vaccination rates, Britain had high levels of virus circulation, due to limited suppression efforts.

The UK's vaccine uptake had slowed in recent weeks, as had rates in the United States.

Britain had effectively adopted a "let it rip" model rather than anything close to an elimination strategy, Baker said.

"Our vaccines work, Covid will be with us forever and we must start to live with this virus as ministers have suggested," Conservative MP Mark Harper told News Corp last Friday.

British Prime Minister Boris Johnson said high case numbers were within parameters predicted for the Northern Hemisphere autumn and winter.

In the US, extensive travel bans are to be ditched next month, but unvaccinated people trying to enter the country will face restrictions.

American vaccine doses peaked at about 3.5 million a day in mid-April and fell until July, when a surge in Covid-19 deaths hit the country.

Te Whanau O Waipareira pop-up vaccination clinic at Larnoch shops, Swanson Rd, West Auckland. Photo / Sylvie Whinray

Rates since July have largely stagnated there at less than one million a day, and the death surge in July continued until September.

Despite much talk of the virus elimination strategy being dumped, Baker said New Zealand still had stricter physical distancing and social gathering rules than the UK.

Baker said there was no doubt more people in New Zealand had Covid-19 than the official tally showed, but there was obviously no way of knowing the true number.

He said some vaccinated people who had Covid would have mild symptoms, or none at all.

Young and healthy people with Covid-19 could also have very mild symptoms or no symptoms.

It was plausible to believe many of these people were not getting tested, he said.

The Delta strain spreading today was the same as that which arrived months ago, Baker said, so no bespoke Kiwi variant had emerged.

He said in the months ahead, complacency would remain a risk even in countries with relatively high vaccination levels, including New Zealand.