It may not be the topic of many conversations now, but more than 1500 people a week are still contracting Covid-19 in New Zealand and three or four people a day are dying from it.

The virus is surging in 84 countries; and at the Olympic Games, dozens of athletes came down with it.

The World Health Organization (WHO) is worried about dangerous new variants. It is a warning we have heard before - and it comes as vaccination rates wane globally.

New Zealander Dr Richard Webby is an infectious diseases researcher at the internationally recognised St Jude Children's Research Hospital in Memphis, Tennessee. He developed a vaccine for the 1997 Hong Kong avian flu outbreak, and is the director of the WHO's Collaborating Centre for Influenza studies.

He told Sunday Morning's Jim Mora that Covid-19 is now endemic.

"The word [endemic] - [and] you ask 100 different scientists what the word means and you'll get 99 different answers - but to me, it means this virus is now in a position to stay. It's going to be with us forever," says Dr Webby.

It was still a disease that could kill people, he says.

A Flourish data visualization

"It's probably a little bit less impact than the first few waves of the virus - there's probably more population immunity now, than certainly the early days.

"But you know, I'd say over the last ... two or three years, it really hasn't dropped that much at all. It has maintained a level of disease-causing capacity that surprises me a little bit."

As with any infectious disease, older people and those with underlying health issues were most at risk, he says.

"It's those folks who are least able to mount a vigorous immune response who are ... more likely to feel the effects of an infection. So whether that's Covid, whether that's flu or ... name your viral disease.

"What we're seeing with this virus is [what] we're seeing with all these others and unfortunately, this is the population that always gets the wrong end of the straw."

In terms of the disease's peak season, scientists initially thought Covid would be a winter disease, but that had not proved to be the case.

"We do seem to [be] continuing to have these summer outbreaks of Covid. Flu has settled back into [being a] winter disease now and RSV - the other part of that trio - again tags along more in the winter months, but doesn't overlap necessarily with flu season.

"We typically associate winter with all the sniffles and colds. Maybe that's not where we are any more. We've got to live with this summer version of sniffles and colds as well."

RNZ