What we know about the Christmas and New Year Covid-19 wave
Friday, 19 January 2024
New Zealand went into the Christmas and New Year period in the midst of another Covid-19 wave — hospitalisations were as high as they’d been since January 2023, and a new variant, JN.1, was starting to gather steam.
So what happened with the wave over the holidays?
Covid-19 modeller and University of Canterbury mathematics Professor Michael Plank says it’s it was a bit of a murky picture over this period for a number of reasons.
There are lags in reporting the data; people have been behaving differently, moving all around the country, and mixing; and tend to be less likely to report positive Covid-19 results — all of which affect the data and make it harder to figure out what’s going on.
So what can we draw from the information we have at the moment?
One, hospital admissions appear to have come down a little bit from a peak, Plank said.
As of midnight on Sunday, January 14, there were 324 people in hospital with Covid-19, down from 355 the same time the previous week, Te Whatu Ora (Health New Zealand) data shows.
The latest wastewater surveillance data, released by the Institute of Environmental Science and Research (ESR) on Thursday afternoon, showed an average of 4.61 million copies of the virus detected per person, per day, in wastewater nationally as at January 14.
This was down from 8.59 million copies detected a week earlier, on January 7.
This could be “consistent with us having passed a peak,” Plank said.
But he noted that wastewater data has been bouncing up and down in recent weeks, and may also be influenced by people moving around the country.
Plank said overall, it’s a bit of a clouded picture, but there are “some indicators” that we may have passed the peak of this wave.
Dr Joanne Hewitt, Science Leader, Health and Environment, at ESR said fluctuations in wastewater week-on-week have been quite noticeable throughout December and January, but didn’t think we could say there had been an indication of a peak.
Looking at the overall trend, national levels had flattened out at a moderate level in December and January, and had been maintained at a “moderate” level for about eight weeks, since around mid-November, Hewitt said.
There has been a general upward trend since about August/September, before a more rapid increase about October and November, she said.
Hewitt said time will tell, as it can take a number of weeks to formulate a true trend of what’s going on.
With further data available next week, particularly around hospital admissions, we’ll start to be clear of the ‘New Year effect’ and have a better idea of the picture, Plank said.
What we do know from looking at ESR’s wastewater data is that JN.1 has continued to increase.
JN.1 is a descendant of the highly mutated BA.2.86 (‘Pirola’) variant.
Earlier in the New Year, the United States’ Centers for Disease Control and Prevention (CDC) said JN.1 was now the most widely circulating variant in the US and globally.
As of January 5, JN.1 was estimated to account for approximately 62% of circulating SARS-CoV-2 variants in the US, an increase from the estimated prevalence of 44% two weeks earlier.
ESR’s latest variant wastewater data shows JN.1 accounted for 48.7% of variants detected in wastewater on a national scale, in the week ending December 24.
This was up from 34% in the week ending December 17.
Plank said this was “as expected” — it had been “pretty clear JN.1 was likely to take over” as it had done in many other countries, and experts had predicted it would become dominant in New Zealand in January.
Given we are now three weeks on from December 24, Plank expected JN.1 would be “well over” 50% by now, and would be dominant.
The CDC says at this stage, there’s no evidence that JN.1 causes more severe disease.
In the seven days to Monday, the number of reported Covid-19 cases was 8040, up from 6558 cases reported the week prior (January 1-7).
The seven day rolling average number of reported cases was 1146, also up on the previous seven days, Te Whatu Ora data shows.