The BA.2 subvariant of Omicron has quickly become the dominant strain of Covid-19 in New Zealand. What is it and what impact will it have on the current outbreak? RNZ is here to clear it all up.
Photo: RNZ / Nik Dirga
Over time viruses change and mutate, creating new variants and subvariants. As we know, there are a number of variants of Covid-19, each given their own letter of the Greek alphabet like Beta, Delta and Omicron. BA.2 is one of several subvariants of the Omicron variant of Covid-19 - not quite unique enough to be given its own letter, though whether it should still have one is debatable.
When you think about Omicron, until now it was likely you're thinking about BA.1, which was dominant in most Omicron outbreaks until recently. BA.1 and BA.2 have differences in genetic sequence, including amino acids and proteins.
BA.2 was first detected in November 2021, around the same time as BA.1 but by mid-March 2022, BA.2 was rapidly gaining momentum around the world.
First found in New Zealand in late-January when a number of border workers and close contacts tested positive, as of mid-March, nearly 80 percent of recent cases that had undergone genomic sequencing here were found to be the BA.2 subvariant.
Though with rapid antigen tests now the dominant form of testing in New Zealand, genomic sequencing is less common than it once was and so it is impossible to know just how widespread a variant is at any one time.
It's highly unlikely you will know whether you've tested positive for BA.1 or BA.2 if you've tested positive for Covid-19.
Director-General of Health Dr Ashley Bloomfield says the prevalence of BA.2 was part of the reason why case numbers in Auckland during the peak of the Omicron outbreak were higher than modelling predicted.
What does this mean for the Omicron outbreak?
While it may prolong the Omicron surge, it's unlikely the rise in BA.2 cases would result in a large second wave as some countries are dealing with, Otago University virologist Dr Jemma Geoghegan told Morning Report.
In fact, she says, seeing a rise in BA.2 at the same time as BA.1 is the best possible scenario and having this happen at the end of summer and among a highly vaccinated population was an advantage too.
Bloomfield says if the majority of cases in New Zealand's outbreak were BA.2 it could act in the country's favour.
He says some places such as New South Wales, the UK and particularly Scotland - were seeing second outbreaks with the BA.2 subvariant, having already had BA.1 subvariant outbreaks.
"Even those jurisdictions that had an initial quite big Omicron outbreak are getting a second one, that seems to be associated with the BA.2 subvariant."
If most of New Zealand's Omicron cases are already the BA.2 subvariant, Bloomfield says there is a chance "we will miss that second big peak again that other countries are seeing".
That's what has happened in Denmark, which saw a rise in BA.2 during its first Omicron wave.
Is it more transmissible?
It's estimated BA.2 is up to 40 percent more transmissible than the already highly transmissible BA.1.
A study of 8,500 households and 18,000 individuals conducted by Denmark's Statens Serum Institut (SSI) found that BA.2 was "substantially" more transmissible than BA.1, though it's important to not this has not yet been peer reviewed.
A separate UK study also found higher transmissibility for BA.2 compared to BA.1.
Data is still limited but the World Health Organisation says people have been reinfected with BA.2 after having had an infection of BA.1.
"Data suggests that antibodies from past BA.1 infection does give you some protection against BA.2, although clearly reinfections can happen, they're probably more rare," Dr Geoghegan says.
Is it more severe?
Director General of Health Dr Ashley Bloomfield says while BA.2 is more transmissible, there is currently no evidence to suggest it is more or less severe.
A risk assessment report from Denmark's SSI in late-February found there wasn't an increased risk of hospital admission associated with BA.2 compared to BA.1. And that's what researchers in England found too.
How effective are vaccines against BA.2 ?
Vaccines appear to effectively shield people against the highly transmissible BA.2 , Geoghegan says.
"The real-world data suggests there's no difference in disease severity between the two variants and the vaccine and boosters appear to be providing really good protection against both subvariants as well."
Health officials in England reported the vaccine was similar in effectiveness against symptomatic disease for both BA.1 and BA.2.
Pfizer boss Albert Bourla told CBS the company is currently trying to make a vaccine that would protect against all variants, and last up to a year.
Both Pfizer and Moderna think a fourth dose of their Covid-19 vaccines - a second booster shot - is necessary as the protection from earlier doses wanes.
How is a new variant found?
PCR testing continues to be used in hospital settings and at the border as part of New Zealand's surveillance regime, allowing officials to detect new variants in the country - this surveillance testing is how officials know BA.2 is on the rise here.
Prime Minister Jacinda Ardern wants New Zealand to become "really sufficient" at surveillance at the border, "gold standard," she says.
Auckland University's Dr David Welch says the border reopening has increased the need for better testing for the virus to guard against new variants.
Can we expect more variants (or subvariants) in the future?
New variants of Covid-19 pop up all of the time and have done since the beginning of the outbreak, whether of not they become a 'variant of concern' is decided by the World Health Organisation. The subvariants of Omicron are currently being monitored by WHO.
"With less stringent border restrictions we expect to see new lineages of viral genomes - genomics enables us to watch these closely," the Institute of Environmental Science and Research's principal scientist and genomics lead Professor Mike Bunce and lead bioinformatics and genomics, Dr Joep de Ligt say in a joint statement.
"Hospital cases are a priority for genome sequencing. The genomic surveillance plan also calls for multiple samples to be taken from patients that have a prolonged infection with Covid-19. The risk here is that the virus, if not 'cleared', can accumulate mutations; we can monitor this by taking samples over time and seeing if key parts of the virus (such as the spike protein) are changing," they say.
"New variants can also emerge in long-haul (long Covid) patients, and there is an increasing awareness of this on the international stage."
Dr Welch says MIQ gave New Zealand a "real time buffer and that time buffer has allowed us to to plan to prepare".
"If we can detect something at the border then you know it would still have to grow inside New Zealand and spread, so spotting at the border rather than once it's already spread widely, could give us a … two or four weeks heads-up."
- additional reporting from BBC