University of Auckland epidemiologist Professor Rod Jackson. Photo / Supplied
An epidemiologist says Covid is 20 to 40 times worse than the flu and is a "deadly disease" for the unvaccinated.
But for the vaccinated, Covid is "far more" like the flu.
The comments come from University of Auckland epidemiologist Professor Rod Jackson, who says getting the vaccine is "a must" and is "incredibly effective" at reducing the severity of the virus.
It also comes as two doctors say Covid is deadlier than the flu.
Jackson compared the flu and Covid by their R values - the average number of people an infected person would infect.
The flu has an R value of 1.5 - this means one person would pass the flu on to 1.5 other people.
After four cycles, five people would be infected. This is achieved by multiplying 1.5 four times.
But Delta has an R value of 6. The vaccine could potentially reduce it to 4, he said.
"In the same time that the flu has infected five people, Delta (even vaccinated) has infected 256."
The virus would infect 1296 people in the same time with an R value of 6.
"That's what makes endemic Covid unmanageable."
Endemic means an infection was "established in the community".
"If it becomes endemic... and we haven't actually managed to get that R value right down to flu-like levels... it will be like the flu on steroids."
If Covid became endemic in New Zealand, Jackson said there would be a "stop-start future".
Unless there were ways to get the R value "way down", there would be "a new normal".
Businesses and schools would have to close for a few weeks and then reopen under this new normal, he said.
The "most acceptable" way to reduce the R value was getting vaccinated.
Wearing masks, physical distancing and ventilation would reduce the R value "a bit" and lockdowns would reduce it a lot, but "no one wants a lockdown", he said.
The vaccine would reduce the R value and reduce severe disease if infected, he said.
"The only way to reduce mortality from Delta is to get everyone vaccinated – this is a must."
Three Lakes Clinic GP Dr Cate Mills, of Rotorua, agreed with Jackson and said the fatality rate of Covid was much higher than the flu.
"We see a lot more young people in ICU with Covid and those people are a lot less likely to survive, so that's what really scary about it.
"If you get to ICU, you've still got quite a high chance of dying."
Mills said people who had recovered from Covid may not necessarily get well again due to the long-term effects of Covid.
But people with the flu normally would, she said.
Mills said the vaccine was the only strategy against Covid to mitigate the effects of the virus and to allow a return to increased personal freedom.
"I just don't want us to have to go through watching people we love die before we improve our vaccination rates."
Fifth Avenue Medical Centre GP Dr Luke Bradford, of Tauranga, said we would "probably" have to accept that Covid would become endemic in New Zealand.
"I don't believe we can continue to be an open society with a world where we shut our borders," he said.
"In order to have a situation where Kiwis can come home and people can go and see their families abroad, it means it will become endemic in the country, unfortunately.
"Therefore, our mitigation strategies have to be good public health control and vaccination."
Bradford said Covid was "without a doubt" more dangerous than the flu for the unvaccinated.
"Covid results in far more hospitalisations and deaths than normal seasonal influenza and it is especially bad for the unvaccinated.
"It's just not in the same category. People who are trying to throw it off as 'it's just a flu' are really misguided."