Two other people who tested positive and completed managed isolation at the Pullman Hotel at the same time as the Northland case are now under investigation. Photo / Peter Meecham
Two other people who tested positive and completed managed isolation at the Pullman Hotel at the same time as the Northland case are now under investigation. Photo / Peter Meecham
A virologist says it's too early to say whether the presence of the South Africa variant was any extra factor in new Covid-19 cases just identified in the Auckland community.
The two people - an adult and a child - have tested positive despite twice testing negative while in managed isolation and being released into the community.
The pair, who completed managed isolation at the Pullman Hotel at the same time as the Northland community case, were asymptomatic and had previously returned two negative tests.
It has also revealed they were carrying the same South African variant, called B.1.3.5.1.
Director-general of health Dr Ashley Bloomfield earlier said there was little epidemiological data available about the strain, but there were indications it was more infectious.
"What we know so far is that it may be more transmissible, but that's not as clear as the information about the variant first identified in the UK," he said.
"There is some evidence that this variant may evade some aspects of the body's immune response."
Otago University and ESR virologist Dr Jemma Geoghegan said it was difficult to say whether this variant played any particular role in transmission within the hotel, given there were so few cases involved.
"We know that, from where this variant is spreading in South Africa for example, it's been recorded to be 50 per cent more transmissible," she said.
"But in our case it's too early to say whether or not this [breach] was because of the new variant, or if it was because of any leaks in [managed isolation and quarantine] procedures."
The Ministry of Health said it was yet to be confirmed if the new cases were recent or historic infections.
Asked how it was possible that the cases earlier tested negative, Geoghegan said it was possible they may have caught the virus toward the end of their stay.
"It may or may not have been after the day-12 test, but it was definitely not at detectable levels when they had the test."
The cases have been described as "weak positives" - but Geoghegan pointed out enough of the virus' RNA was intact to generate genomes that showed the samples' genetic make-up.
"Weak positives" are more typically those samples where there's very little of the virus to extract, either because of the infected person having a low viral load, or simply because of the way the sample was handled.
RNA was a fragile molecule that could degrade quickly when damaged by light, heat and chemicals - and such could be expected with samples, even when handled and stored in ideal conditions.
Otago University and ESR virologist Dr Jemma Geoghegan said it was difficult to say whether the South African variant played any extra role in the latest cases of transmission. Photo / Supplied
Nonetheless, scientists can often build up genomes from samples with low levels of RNA, through extracting and sequencing the material multiple times.
It was also expected serology testing of the new samples would provide officials a clearer picture of how the infections occurred.
This test measured antibodies that the body made in response to infection, and it generally took 10 to 14 days after an initial exposure to the virus before someone had enough to test positive under it.
"That means if someone was infected in the last few days they are less likely to be positive by serology," University of Auckland immunologist Dr Nikki Moreland said.
"So serology testing could provide another piece in the puzzle in determining the infection timeframe on these cases."
Twelve people also tested positive in the Pullman between December 30, when the Northland woman arrived, and January 25.
All of these cases were transferred to the Jet Park Hotel quarantine facility.
Otago University infectious diseases expert Professor David Murdoch said the emergence of new variants at our border also needed to be put into a global context.
"If you look at where people are coming from - and the kind of mixing that's happening around the world, even in the Covid age - the chances of new variants coming to New Zealand are pretty high."
Murdoch said the higher risk factor that came with these variants under-scored the importance of the hard measures New Zealand had taken to secure the country against Covid-19.
"This should just reinforce the rigorous approach that we take for any case here."
