New Zealand is facing a second wave of coronavirus infections as cases of the Omicron subvariant BA.5 spread around the country.
The BA.5 subvariant may be leading a new wave of Covid-19 infections. Photo: RNZ / Liu Chen
The Ministry of Health yesterday reported 4924 community cases of the virus and the deaths of 11 people with Covid-19, but the seven-day rolling average has grown to 6895, almost 2000 more than a week ago.
The BA.5 subvariant appears more transmissible and better at evading immunity than others and is expected to overtake BA.2 as the dominant strain within weeks.
University of Canterbury professor and Covid-19 modeller Michael Plank said infections could potentially hit a similar peak to the first March wave of around 20,000 cases per day.
"We can see in the genome sequencing data that this variant has been spreading much faster than the previous variant that we have, so it's quite likely that this will lead to a significant second wave in the weeks ahead," he said.
"It's certainly possible that we could have a second wave that's comparable in size to the first wave back in March, at least in terms of the number of cases."
Plank said the number of infections among people over the age of 70 were already at an all-time high, as immunity from vaccination and first wave infections waned.
"Quite concerningly we've seen the biggest increase in older age groups, which is of course where the biggest risk of severe illness is," he said.
While it was difficult to predict how long a second wave might last, Plank warned it could be a month or two.
University of Otago epidemiologist professor Michael Baker earlier told RNZ the surge in infections suggested the next Omicron wave was coming.
He told First Up the data on the second wave was plausible.
"It's always unpredictable because the wild card is the virus because it's changing, and we are now getting these new subvariants Omicron BA.4/5 and another one that are taking over.
"These are more transmissible because they escape the immunity we've already got. We can be pretty sure the numbers are going to go up, and it may be quite sustained.
"You can get reinfected within three weeks, and this is getting very common and it will get to a point where that's the norm that you're being reinfected. And unfortunately, every time you get this virus, you face all the same problems."
He said changing the country's traffic light settings from orange to red was not necessary just yet.
Apart from vaccination, he said self-isolation early on when symptoms show, and wearing masks indoors around other people worked to slow down the virus spreading.
"We need to mandate masks in schools because there's a lot of transmission happening there. The great thing about isolation and masks is they work on all Covid variants, influenza, RSV and all the other respiratory viruses."
"It will get to a point where that's the norm that you're being reinfected" - University of Otago epidemiologist professor Michael Baker
A second wave is likely to put hospitals under enormous strain as they deal with Covid-19 and flu patients, along with people suffering from other respiratory illnesses.
A second booster - or fourth dose - is now available for everyone over 50, as well as health, aged-care and disability workers over the age of 30.
Covid-19 Response Minister Ayesha Verrall last week said the country would remain at the orange traffic light setting.
"The wave really seems to have started now" - University of Auckland computational biologist David Welch
University of Auckland computational biologist David Welch told Morning Report rising numbers were going to add even more pressure to already stressed hospitals.
"The hospitals are already operating at pretty much peak capacity, as they typically do through the winter flu season. This will only add a lot more pressure to it. In the first wave we were in the red alert level setting, so it was reduced contacts and that was flattening the curve a little.
"At the moment we're in orange so it remains to see whether there will be enough to flatten the curve to keep our last at hospitals operating properly."
The government needed to assess cases and if it was time to go up to the red light setting, he said, adding that schools should mandate wearing masks.
Many people now had waning immunity and were at risk of being infected or reinfected, Welch said.
"We estimate that the proportion of cases of BA.5 makes up is roughly doubling every couple of weeks. So, it's a significant growth advantage ... even a bit more than what BA.2 had over BA.1.
"The wave really seems to have started now. Over the last week, we've seen pretty consistently cases being higher than they were a week earlier, and that's the first time we've seen that kind of sustained growth in cases across the country for several months."