The BA.4 Omicron variant has arrived in New Zealand via a traveller from South Africa.
It's reported to be driving a new wave of Covid-19 in South Africa, but here in Aotearoa authorities say it's no more transmissible or severe than other Omicron variants.
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The basics
The BA.4 variant is one of the different Omicron subvariants being monitored by the World Health Organisation, which says it may have "a growth advantage."
However, the Ministry of Health says there is no evidence to date that it is more transmissible or causes more severe disease than other Omicron lineages, in particular the BA.2 Omicron sub-variant that is causing the vast majority of infections in New Zealand.
BA.4 has been reported in Southern Africa and Europe, and a case was reported in New South Wales a few days ago.
According to a UK Health Security Agency report from early April, cited by other media, "the earliest BA.4 sample in GISAID was from South Africa with a sample collection date of 10 January 2022".
Although the number of BA.4 was low, the fact it had already been detected in South Africa, Denmark, Botswana, England and Scotland at that point showed it was transmitting successfully, the report said.
How was the case detected?
The MOH said the person arrived in New Zealand from South Africa on 22 April, returned a positive RAT the following day and a positive PCR test on 24 April.
"Whole genome sequencing was undertaken as part of ongoing border surveillance for emerging variants and subsequently confirmed the BA.4 variant.
"The person followed all testing and reporting requirements, allowing this new sub-variant to be identified quickly, and has been isolating at home.
Variants arriving in New Zealand has been expected, with Director-General of Health Dr Ashley Bloomfield saying they are "inevitable".
Today, the Ministry of Health said "the arrival of this sub-variant in New Zealand is not unexpected".
"At this stage, the public health settings already in place to manage other Omicron variants are assessed to be appropriate for managing BA.4 and no changes are required."
University of Otago virologist Dr Jemma Geoghegan said BA.4 was a relatively new variant and there was not much hard evidence about it.
But she said it seemed it could reinfect people relatively easily, and spread quickly.
"It's most likely got an advantage over BA.1 and BA.2, so BA.4 and BA.5 as well have got mutations which suggest it could evade immunity and that means previous infection and vaccines might not give that much protection against being reinfected."
South African scientists from multiple institutions were examining BA.4 and BA.5. They took blood samples from 39 participants previously infected by Omicron when it first showed up at the end of last year.
Fifteen were vaccinated - eight with Pfizer's shot; seven with J&J's -- while the other 24 were not.
"The vaccinated group showed about a 5-fold higher neutralisation capacity ... and should be better protected," said the study, a pre-print of which was released over the weekend.
In the unvaccinated samples, there was an almost eightfold decrease in antibody production when exposed to BA.4 and BA.5, compared with the original BA.1 Omicron lineage. Blood from the vaccinated people showed a threefold decrease.
What do the experts say about omicron variants in general?
In mid-April, Covid-19 modeller David Welch said new subvariant strains would not cause waves of new cases if they arrived in New Zealand, but would likely leave a long tail of case numbers.
The subvariants were likely to keep case numbers up to about a thousand a day in New Zealand, Welch said.
"The variant mix might change a little but there's nothing to suggest at the moment that we're going to get a really big new wave or even that these new variants being reported are really going to change the landscape."
Welch said the subvariants are not any more contagious than Omicron at this stage.
"Some of the variants that have been reported on recently like XE, also like BA.4 and BA.5, yes they are different, they might have slightly different behaviours, but they're not going to be ... the game changers that we've seen with Alpha, Delta or Omicron."
- RNZ w/ Reuters