Covid 19 coronavirus: The number of coronavirus cases is up, should we be worried?

The number of new coronavirus cases announced today was the highest in nearly a week, but experts say to be vigilant, not worried.

Nine new cases of the virus were announced today, the highest in the last six days.

While the number of new Covid-19 cases has been in single figures for the past seven days in a row, Director-General of Health Ashley Bloomfield has urged Kiwis to remain vigilant.

"As we prepare to move to alert level 3 on Tuesday morning, it's really important not to slacken off the effort," he said.

With concerns of New Zealanders getting complacent under the last week of alert level 4, epidemiologist Michael Baker warned that there was a better chance of eliminating the virus if people followed strict rules.

Despite today's uptick in cases, Professor David Murdoch of Otago University said it wasn't a cause for concern.

"What we're looking at is the overall trend rather than the daily variations, so we will see ups and downs in the daily count of cases," he said.

The change in the daily numbers could be due to a number of things, from when the tests were processed, to when the public health board was notified of the new cases, rather than when they fell ill.

Instead, it was important to pay attention to the overall trend of the case numbers, which was going down, Murdoch said.

And the fact that the numbers were so low might mean that the changes seemed more dramatic than they are, Otago University's Dr Ayesha Verrall said.

"When you have low numbers, the variation around them can appear high, so you can go from four to eight and it looks like a bigger change," she said.

"The most important thing is to look at the overall trend - if you look at this week compared to last week, we're in a better place."

Vital to understanding the current trends was linking all of the related, confirmed Covid-19 cases, Murdoch said.

Of the 16 significant clusters of infection, the Ministry of Health was unsure of the origins of six.

"Very few cases have popped up without any clear source," Murdoch said.

"That's the really important piece of information, most of the clusters seem to have connections.

"If there was asymptomatic spread to a major degree, we would see a lot more cases."

There have now been 1470 confirmed cases of the coronavirus, which has killed 18 people.

Some 1142 people have recovered, an increase on 24 compared to yesterday.

Verrall said that public health authorities should always be looking to improve their understanding of the significant clusters and their origin.

"In the last week, the majority of cases were imported - related to overseas travel - rather than local," she said.

"It's Important to track each cluster in detail and to be confident in the controls around them.

"The public health system needs to know who the confirmed cases are and that they are taking the appropriate measure in isolation."

As we reach the last day of lockdown, now was not the time to slacken your efforts, Murdoch said.

"It worries me that people may relax too much," he said.

"The key thing is, we've invested too much to go backwards."

• Covid19.govt.nz: The Government's official Covid-19 advisory website