What you need to know about BA.4
The Ministry of Health is relatively relaxed about the arrival of new Omicron variant sublineage BA.4, but it’s early days in the new generation of Covid-19. Chris Hyde reports.
Let’s start with a metaphor. A few months ago BA.2 was the Jack Lovelock of Omicron; fast, enduring and unbeatable at its peak.
BA.2 has been so transmissible that well over a million Kiwis (and counting) have caught it. It’s completely outcompeted the original Omicron subvariant known as BA.1.
But now it’s May, and the next generation of Omicron variants have arrived at our shores.
BA.4, the recombinant Omicron variant XE and also BA.2.12.1 and BA 2.12.2 are starting a new race with BA.2.
Another version of Omicron, BA.5, is likely to join them in coming days or weeks.
What we know so far from early scouting is that all of these sublineages of Omicron could potentially beat our 1500-metre specialist Lovelock (BA.2) over the first 100 metres.
But we have no idea what the rest of the race looks like. There’s still six turns to take yet, and there might even be a few hurdles placed in the way.
It’s certainly possible for BA.2 to win over BA.4, BA.5, BA.2.12.1, BA 2.12.2 and XE.
But if it doesn’t win the race – if any of the others outcompete it – a second wave of Omicron becomes much more likely.
Who are these new runners in the Omicron race?
The first case of BA.4 was announced over the weekend by the Ministry of Health and then another on Monday.
It joins recombinant variant XE (which early study suggested had a 10% transmission advantage over BA.2) at the start line.
The public health settings already in place to manage other Omicron variants are appropriate for managing BA.4 and no changes to restrictions are required, the ministry says.
Firstly, it’s important to remember that BA.4 is still Omicron, and not as severe as Delta.
Where it differs is in extremely subtle changes to its genetic make-up that scientists believe could compromise our Covid immunity, brought on by vaccination and infection.
BA.4, like BA.1, was first detected by South Africa’s genome sequencing teams, and in combination with BA.5 it appears to be starting to cause a fifth wave of cases in the country.
In a pre-print study released over the weekend, South African scientists said the two new sublineages can dodge antibodies from earlier infection.
Evolutionary virologist Dr Jemma Geoghegan, of the University of Otago, said initial estimates suggested BA.4 had a transmission advantage over BA.2 of 8%, and BA.5 had a 12% advantage. This essentially means both have a higher percentage chance of infecting you or me.
The combination of these two factors has Alex Sigal, a professor at the Africa Health Research Institute in South Africa, confident of a new wave of cases.
However, Signal doesn’t
believe it will necessarily mean a wave of severe health impacts for the world. Those who are vaccinated will be better off.
‘‘The vaccinated group showed about a 5-fold higher neutralisation capacity . . . and should be better protected,’’ said Sigal’s study.
Geoghegan said a wave of new cases won’t necessarily happen in Aotearoa, because South Africa’s population and immunity profile is so vastly different.
Its big Omicron wave was caused by the original BA.1, and its rates of vaccination are very low – about 30% of its total population are fully vaccinated.
‘‘I think we’ll learn more about BA.4 and potentially BA.5 when they are established in other areas of the world outside of South Africa that have been through a BA.2 wave,’’ Geoghegan said.
‘‘We need to monitor a country that had a big BA.2 wave like us and understand the impact of these new variants on them.’’
The beginning of South Africa’s fifth wave also coincided with a period two weeks after Easter, Passover and Ramadan – all celebrated with gatherings across the country, she said.
‘‘You can’t ignore the role of these compounding events, but nevertheless it looks like the advantage is real.’’
Most importantly, at the moment there had been no sharp rise in excess deaths in South Africa, Geoghegan said.
‘‘So you could say it’s probably unlikely to result in more severe disease, but again, it’s still pretty early.’’
One of the most interesting aspects of South Africa’s population is that health experts estimate its total Covid infections since the pandemic began are now even higher than the number of people living in the country.
Essentially many people who have caught one strain of the virus have now caught another due to either waning immunity or a variant escaping the immunity brought on by an earlier infection.
The next worldwide variant of concern, whatever it is, is bound to be one that can escape immunity, Geoghegan said.
‘‘Most of the world has either had some protections against the virus from past infection or from vaccines, so that will provide the biggest advantage for new variants.’’
When it comes to BA.2.12.1 and BA 2.12.2, we know even less than BA.4, but the pair are thought to be behind an uptick in cases in the US state of New York.
The Centers for Disease Control and Prevention says they’ve rapidly spread in the northeast of the US in particular, and BA.2.12.1 now accounts for the majority of new infections.
In one part of New York state, the pair of them now account for more than 90% of new infections.
Preliminary CDC research suggests both are about 25% more transmissible than the BA.2 subvariant, which, if it holds true, would make them the most highly transmissible strains of Covid identified to date.
Again, in itself, this is not a big deal, because it’s only the very beginning of the race.
The ministry says both were found for the first time in New Zealand in travellers arriving on April 11 and April 15.
‘‘Neither sub-variant is currently regarded as being of concern,’’ the ministry said.
Geoghegan said the rapid changes and rapid emergence of new strains – ‘‘I can’t really keep up with them’’ – highlights just how crucial genomic sequencing and surveillance of new cases would be in the coming months.