The Government now says the “leading hypothesis” for the source of the Valentine’s Day outbreak involves seven weeks of undetected community transmission, Marc Daalder reports
Covid-19 may have crept along the border or spread silently through the community for seven weeks before it was caught earlier this year.
The “leading hypothesis” for the origin of the Valentine’s Day cluster now links those cases to a returnee who tested positive in managed isolation in December. For the cases to be connected, several links in a chain of transmission would have had to have gone undetected for seven weeks, until February 14.
That the Government now suspects it missed this transmission was first tacitly admitted by Covid-19 Response Minister Chris Hipkins in response to a Written Parliamentary Question from National Party Covid-19 spokesperson Chris Bishop.
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Bishop asked for any updates on the investigation into the origin of the Valentine’s Day outbreak, which saw Auckland locked down twice and the reactivation of the wage subsidy programme.
While Hipkins said he had been “advised that there is no obvious source for the outbreak despite several hypotheses being investigated,” he also said the “leading hypothesis is that this cluster is the result of a border incursion from this [December MIQ] case”. While an employee who did laundry from international flights at Auckland Airport was originally suspected to be the index case, Hipkins indicated that employee’s daughter had in fact been first in the chain of transmission.
This is a change of stance from earlier in the year. When the genomic link between the cluster and the MIQ case was first noticed, officials reported, “It is important to note that health officials consider this an unlikely source of the infection at this stage but are pursuing it as part of actively chasing down every line of enquiry”.
Hipkins’ office referred a request for comment from Newsroom to the Ministry of Health, which responded: “The Ministry of Health is confident that with the amount of testing done around the wider Auckland region during this cluster, there is unlikely to have been widespread undetected community transmission. Investigations by Auckland public health officials have also satisfied us there is minimal risk to the community of ongoing transmission from the cases in this cluster.
“Person-to-person is considered the most likely cause of infection in this case based on international evidence which has found fomite [surface] transmission is unlikely. This is a tricky virus. And we know with our experience with other clusters, such as the Americold cluster last August, we don’t always find the source of infection.”
However, several experts told Newsroom it was “highly unlikely” that the MIQ case could have been the source of the cluster. The virus – which was the more transmissible B.1.1.7 variant – would have had to jump along a linear chain of transmission without branching out and infecting others. Mass testing of the community in January – after the discovery of the Northland case and the associated Pullman Hotel outbreak – and during the Valentine’s Day cluster turned up no cases that weren’t connected to Papatoetoe High School.
“It seems highly unlikely to me,” University of Auckland microbiologist Siouxsie Wiles said.
“Given what we know about this virus, it seems highly unlikely. That seems one of the least likely things to me, that we had seven weeks of transmission we don’t know about.”
Jemma Geoghegan, an evolutionary virologist at the University of Otago, told Newsroom that the virus genomes from the Valentine’s Day cluster and MIQ were very similar.
However, that wasn’t as strong a hint that the cases might be connected as in other scenarios.
“Genomically, it was linked. But we have to think back to that time: December, January, February was the time when B.1.1.7 was increasing in frequency and exploding, really, around the world,” she said.
“During that first explosion of a new variant, there isn’t much diversity that you can see between cases. So two cases that look like they might be linked might in fact share an ancestor many transmissions ago. It’s really hard to make those conclusions from the genomics.”
The hypothesis can’t be ruled out, but it remains unlikely. Still, Hipkins told Bishop in the written answer that other theories – including the worker being infected via the laundry – were also unlikely.
“I am advised that given international evidence, fomite [surface] transmission is unlikely, especially on soft materials such as those going to a laundry. Person-to-person transmission is the most common and likely for SARS-CoV-2,” Hipkins wrote.
Joep de Ligt, the head of bioinformatics at ESR, told Newsroom that judging a front-running theory was difficult.
“Something unlikely must have happened, ranking those unlikely events in terms which is least unlikely is an interesting exercise especially with missing data,” he said.
“[Public Health Units] did a lot of leg and lab work to try to find a potential missing link and did not find one.”
Hipkins also wrote that the investigation was effectively closed.
“The Auckland Regional Public Health Service source investigation activities have been exhausted to satisfy our purpose of ensuring there is minimal risk to the community of ongoing transmission. These activities included investigation into case workplaces, airport, managed isolation facilities and returnees connected to these facilities.”
This echoed the statement from the Ministry of Health.
“In investigating this cluster, we conducted extensive testing of past guests at the Four Points Sheraton. Despite this additional testing, no definitive source has been identified and the cluster is now regarded as closed,” the ministry spokesperson said.