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The level 2 light at the end of the tunnel for Northland and the Waikato is getting brighter, but the number of active mystery cases in Auckland has jumped five-fold since a week ago. 

That increase is seeing greater scrutiny on preventing the virus from being carried out of the city, following cases that have already taken Covid-19 from Auckland to Palmerston North, Waikato and Northland. 

In the most recent border breach, a 22-year-old Auckland woman yesterday pleaded guilty in the Whangārei District Court on one charge of failing to comply with Covid restrictions under the Public Health Act 2020 by travelling outside of Auckland without a personal travel exemption. 

The woman, who was subject to court-imposed conditions at the time, hid in the boot of a car and travelled to Northland on Friday last week. 

"It's clear that the outbreak in Auckland is getting worse, so it's crucial to look at measures of slowing regional spread," Covid-19 modeller Professor Michael Plank said. 

Auckland cases were doubling about every 12 days on average, which could see daily case numbers climb to 160 by early November, he said. 

"The virus has leaked out on several occasions now, and with some of the region's low vaccination rates, it would be devastating if the virus found its way into those communities." 

Those leaving Auckland need to be tested, but don't need to wait for a negative result before crossing the boundary. 

They can also bypass the testing requirement with a medical certificate saying they don't have symptoms. 

The Government will today reveal alert level decisions in Northland and the Waikato, as well as provide an update on when schools in Auckland might open, having pushed back the initial October 18 date. 

Yesterday there were three cases in the Waikato, but they were household contacts and already in isolation. There are no unlinked cases, and testing rates have remained high. 

Plank said level 2 in the Waikato from Friday looked like a safe move, provided there were no surprises in today's case numbers. 

Level 2 prospects for Northland are a bit murkier, but health officials hope to know more about the level of risk after talking to one of two people who travelled from Auckland to Northland and back in early October. 

She was picked up in west Auckland by police on Monday night, moved to the Jet Park quarantine facility, and is said to be cooperating with contact tracers. 

She is one of her travel companion's 18 close contacts across Auckland, Northland and Wellington - and the only one who has tested positive. 

Last night a new location of interest was added to the previous six in Northland - a Subway eatery in Whangarei. 

Plea for pregnant women to get jab 

An Auckland obstetrician has encouraged pregnant women to get vaccinated. 

Dr Michelle Wise said studies had shown that of the pregnant women hospitalised with Covid-19, most had not had their jab. 

"Almost all of them were not vaccinated or had just one jab, that just shows you how effective the vaccine is in pregnant women," she told TVNZ. 

Wise said it was definitely safe to have the vaccine during pregnancy and there were no risks of miscarriage. 

She said people who contracted Covid-19 during their pregnancy were more likely to have complications including giving birth early,before 37 weeks. 

International studies showed there was no impact on fertility and Wise said there was "no plausible mechanism" it could affect women or men in terms of conceiving in future. 

Even people having IVF had been monitored and were not affected by the vaccine. 

"Women having IVF, their egg quality was the same… and males were not affected," she said. 

"All the metrics are exactly the same whether they are vaccinated or not." 

She said there were a lot of questions about whether the vaccine could pass on to an unborn baby from its mother. 

"The vaccine itself breaks down in body in a couple of hours," she said. 

But it created "amazing antibodies" in the mother's body that were passed on to their baby and helped strengthen immunity. 

"We certainly see added benefit immunity in babies," said Wise. 

She encouraged pregnant women to vaccinate as soon as possible - but acknowledged there was a level of nervousness and even fear in some expectant mums. 

"I understand being nervous about it … who do you trust?" she said. 

"I would say make sure you're getting your information from people that you trust, not from the internet. 

"Midwives, nurses, obstetricians - we are all vaccinated and we spend all of our time answering questions. 

"We are all vaccinated to protect you now we want you to be vaccinated to protect yourself." 

Epidemiologist Professor Michael Baker said it wouldn't necessarily be premature to move Northland to level 2 from Friday. 

"It can be done - if the only evidence you've got is a single intrusion, and you've got some information about the extent of that and their contacts, and there's no evidence of spread. 

"It's very different from Auckland, where you've got entrenched transmission for weeks." 

There were 40 new cases in Auckland yesterday, and the number of unlinked cases over the past fortnight climbed to 74. 

The number of such cases has climbed every day since October 6, when there were 15 unlinked cases over the previous fortnight. 

"The most meaningful total is the unexplained cases, which tell us about the potential size of the iceberg of undetected cases," Baker said. 

"All the indications are going up, and we still haven't seen the full effects of the slight loosening of level 3, with picnics." 

Baker said the measures around the Auckland boundary were "weak", noting that people leaving the city had to be tested within the last seven days, but didn't have to wait for the result. 

It's unclear if the Northland travellers, who procured travel permission under false pretences, had shown evidence of a test or had a medical certificate before they were allowed to leave Auckland. 

"The system is very loose," Baker said. 

"If we're serious about the Auckland boundary, there should be a requirement to be vaccinated, and to have a test taken within three days of travel and a negative result - no exceptions." 

Plank added that rapid antigen testing - which is less sensitive but has picked up a case in Middlemore Hospital - could complement the PCR testing requirements. 

"None of those measures are perfect, but they could help to delay the spread of Covid. If it buys us even a few weeks to get more people vaccinated, it would be worth it." 

Prime Minister Jacinda Ardern hasn't ruled out mandatory vaccinations for those crossing the boundary, but it already took time to check everyone's testing status and evidence for why they can travel. 

"We have thousands of people legitimately travelling. Adding in the ability to check vaccination status and indeed ensure that those goods and services are still able to move ... would take some time to stand up. 

"It isn't straightforward, but it isn't one that we've dismissed out of hand." 

Instead of antigen testing - which is only at the pilot stage - director general of health Ashley Bloomfield said he was looking at requiring travelling workers to be tested more frequently. 

"We're really keen to make sure that boundary is as tight as possible to help avoid spread."