‘Our most dangerous phase yet’
As New Zealand moves out of lockdown, new cases of Covid-19 are still emerging. Two leading scientists explain why to Emma Russell
New Zealanders have spent the last month at home to stop the spread of Covid-19. Their reward started yesterday with the resumption of freedoms such as ordering takeaways and the chance to take a dip at the beach.
Yet, each day for the last week, a handful of new cases has continued to pop up. Michael Baker, an epidemiologist and public health physician with the University of Otago and a professor in the Department of Public Health, says though our country is well on track to stamping out the virus it may be too early to say we have eliminated it.
“We cannot say we have eliminated Covid until we have strict criteria for sustained chains of transmission.”
By that, he means having a rapid response plan in place so that outbreaks can be prevented whenever a new case appears, which includes quick, effective contact tracing and constant randomised testing.
Asymptomatic spread
Baker says one of the reasons we are seeing new cases is due to the high number of asymptomatic cases — people who carry the virus but do not have any symptoms.
“For example, someone who is young and fit could be asymptomatic for 10 days before passing it on to someone else in their bubble, who could also have no symptoms, and so on, until someone catches the virus, who does show symptoms.”
He says “we are entering our most dangerous phase yet” as asymptomatic people are potentially coming into contact with more people.
Infectious disease expert Dr Siouxsie Wiles has a different theory.
She says we haven’t seen any asymptomatic cases of Covid-19 but rather pre-symptomatic, “and there’s a massive difference”.
Pre-symptomatic is when a person doesn’t show any symptoms within the first few days of contracting the virus — which is when they risk infecting others — but eventually, they do get symptoms, even if mild, and that’s often when they are less at risk of passing it on. For this reason, Wiles says pre-symptomatic cases are unlikely to be the reason we are seeing new cases.
“We don’t have a high number of people who are pre-symptomatic, because if they were transmitting it without knowing then we would see a high number of people needing to be hospitalised.
“The fact our rates of hospitalisation are really low is helping our understanding that we don’t have a large number of people in their bubbles who don’t know they have the virus.”
Overseas travellers
Wiles says many of the new cases are likely to be people who had arrived in New Zealand from overseas.
If they are following strict quarantine regulations then the risk of them infecting others is low, she says.
“It would be good to get some more information from the Ministry of Health on this, and more detail about the clusters.”
Bubble breakers
Wiles says another reason we are likely seeing new cases is due to people “expanding their bubbles” or “breaking bubbles”, which is when clusters often arise.
“I have heard of people who have, for example, decided their definition of a bubble is their whole street because that means they can still have dinner with each other and do activities together.
“The question is how many have done that and not got away with it?
For example, imagine if one of those people on the street had been part of a cluster without realising.”
Delayed testing
A Taranaki woman tested positive for Covid-19 after arriving in the country more than two weeks ago.
Wiles says the woman delayed getting tested because her symptoms were so mild.
“By the time she did get tested she was no longer infectious but still tested positive because she had small shreds of the virus in her body that weren’t in any way damaging.”
Director-General of Health Ashley Bloomfield says the testing of mild symptoms is key to moving down to alert level 2, including a loss of smell or taste.
He says a 12-day delay in getting a test result is unacceptable, but adds that a negative test confirmation might take longer than a positive result.
Yesterday was the 10th straight day of single-digit coronavirus cases, with only three new cases reported yesterday afternoon — and 239 active cases in total.
Bloomfield is warning people to keep their distance as they rush to buy takeaway coffees and hamburgers. “We do not want to see the sorts of rebounds we have seen in other countries.”