Epidemiologists have warned for several weeks now that a fresh wave of Covid-19 cases, fuelled by new variants of the disease, could be on the way and southern case numbers seem to confirm that is happening in Otago and Southland.
In Queenstown-Lakes, where the new BA2.75 subvariant was detected a fortnight ago, reported active cases have hiked from 74 on October 23 to 105 on October 30.
BA2.75 is now accounting for 10% of the wastewater detection rate in Queenstown Lakes.
Meanwhile, the highly transmissible BQ1.1 variant is surging in Christchurch, where water testing suggests the variant accounts for 20% of Covid-19 cases.
The new variants have not as yet shown up in meaningful rates at other southern water testing places, but given their high reproduction rate, overseas experience suggested they would become more widespread.
Reported cases, which almost always lag substantially behind actual case numbers suggested by wastewater testing, have risen in all southern centres, dramatically so in some places.
In the week from October 23-30, active cases in Dunedin soared from 348 to 564, and in both Southland and Waitaki active cases almost doubled, from 49 to 81 and from 35 to 63 respectively.
Cases in Central Otago rose from 38 to 61, in Clutha from 65 to 84 and in Gore from 38 to 65.
Invercargill’s active cases rose modestly, from 241 to 250, but three weeks ago sat at just 91.
The Institute of Environmental Science and Research’s latest wastewater report largely mirrored the official statistics: of the 11 testing stations across Otago and Southland, Covid-19 prevalence was up in eight. It was steady in Invercargill, but slightly down at two of the three Dunedin testing sites.
Covid rates in Wanaka were at their highest since mid-August, when the Omicron wave was abating, while in Balclutha and Queenstown prevalence rates were approaching the same levels experienced during the Omicron peak.
"Many sites, particularly those across the central regions of New Zealand, showed marked increases in viral levels," the ESR said.
In the week ended October 16 56% of sites nationwide showed an increase in Covid-19 in wastewater and 22% of
sites showed a decrease.
"The results suggest that case rates are 43% lower than would be expected based on the SARS-CoV-2 levels in wastewater."
Last week the ESR’s head of bioinformatics and genomics, Joep de Ligt, warned that New Zealand faced the risk of a "soup" of new variants sweeping the country, and that people who had resisted earlier strains of Covid-19 could be vulnerable to a new variant.
"The only safe prediction is that there is going to be a wave. How bad it is is going to be is partially dependent on people's behaviour but also these new variants — and they are around and they are causing waves — and we will lose loved ones."
The Ministry of Health is expected to make its weekly release of national Covid-19 statistics today.
Last Monday it reported 20,532 new cases nationally (up from 16,399 the week before) and 1277 new cases in Otago and Southland.
