The possibility of the Delta variant of Covid-19 spreading in New Zealand is concerning, because it is 50 to 100 percent more infectious, says University of Otago evolutionary virologist Jemma Geoghegan.
Health officials are working under the assumption that a Sydney man with Covid-19 who visited Wellington last weekend has the Delta variant.
"The recent report from Public Health England... really underscores the Delta variant's adaptability to be able to spread more than even the Alpha variant, which was highly contagious and first noticed at the end of last year," Geoghegan said.
"We're getting estimates of between 50 to 100 percent more transmission even compared to the Alpha variant - which is pretty concerning."
New public health measures might be needed to combat the more contagious strain, she said.
"Our measures were set up in a hurry and also over a year ago when the picture looked quite different.
"With the emergence of more transmissible variants and potentially ones that could evade some effect of the vaccine, it's likely that we need to have a look at the measures and I'm sure epidemiologists are actually doing that."
UK data suggested the Pfizer and AstraZeneca vaccines offered the same level of protection against the Delta variant as other strains, she said. People who have received two doses of the vaccines continue to be protected against hospitalisation and serious illness if they contract the Delta strain.
However, those who have not been vaccinated are at risk of more serious effects from the new strain.
"The data suggests that for those who have not been vaccinated, people might be up to twice as likely to be hospitalised if they've been infected with the Delta variant, compared to the other variants."
Geoghegan said some different and more severe symptoms had been reported from the Delta strain.
It was important that Covid-19 vaccinations were available worldwide, to keep the coronavirus from proliferating and adapting in ways that made vaccines less effective, she said.
"There's not much point vaccinating ourselves but letting it spread uncontrolled elsewhere, rendering our vaccines potentially not very effective.
"As long as the virus can replicate and infect new cells and then spread to a new host, it's going to be able to change.
"It's adapting, it's better able to spread between humans and also to escape any human response we have from either being infected or from vaccination."
The virus was evolving quickly, she said.
"What we're seeing is these subtle changes in the proteins of the virus, change in shape and ability to infect our cells and replicate - that's why people are becoming more contagious ... and that's why it's increasing in frequency around the world."