There have been 20,522 new Covid-19 cases reported across New Zealand in the past week – up from 16,399 last week. There are 676 cases reported in the Bay of Plenty.

The Ministry of Health is also reporting 11 deaths attributed to Covid-19.

Last week the seven-day rolling average of new daily cases was 2343, an increase on the 2041 on the previous week.

Unlike previous waves, which were driven by one variant or subvariant, this latest increase has seen a variant alphabet 'soup” emerge.

The World Health Organisation (WHO) is tracking more than 300 Omicron sublineages (or subvariants) worldwide.

All Omicron subvariants were showing 'increased transmissibility and properties of immune escape”, WHO Covid-19 technical lead Dr Maria Van Kerkhove says.

Two subvariants officials are keeping a close eye on due to their growth advantage, BQ.1.1 and XBB, both grow faster than the previously dominant BA.5 strain.

New variants and subvariants are popping up on New Zealand shores. Image: Sungmi Kim/Stuff.

Professor Mike Bunce​, principal scientist, genomics lead at ESR (the Institute of Environmental Science and Research) says recently the 'steady increase” in cases over recent weeks was more about measures being relaxed – such as removing mandatory masking – than new variants.

But these new subvariants are arriving, and it's 'highly likely they're going to bite at some point”.

'The million-dollar question is: how steep will this be, how rapid, and how protected New Zealand is” with regard to immunity, he says.

- Troels Sommerville/Stuff.