Covid-19 NZ: Understanding the Omicron variant BA.5 and why it’s fueling a second wave

The second Omicron wave seems to have started. Case numbers – along with hospital admissions – are trending upwards.

Behind it is the rise of a new Covid subvariant called BA.5, which experts suspect is starting to snowball.

This is a snapshot of what’s going on and what you need to know.

What is BA.5?

Alpha, Beta, Delta, Omicron – all are different Covid-19 variants. Just like BA.1 (which was dominant here) and BA.2 (which is now dominant), BA.5 is another member of the growing Omicron family.

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This particular variant was first spotted in South Africa earlier this year, but has popped up all over the world.

It appears to have a growth advantage over BA.2 for two reasons – it is more contagious and better at bypassing existing immunity.

As Nature Both BA.4 (another Omicron flavor) and BA.5 are reportedly more similar to BA.2 than BA.1 – the original or vanilla Omicron strain that reignited the pandemic late last year. We’ll come back to that.

What have we seen so far?

BA.2 has been topping the Covid charts in New Zealand for some time.

But that is changing. As newsroom As of early June, only a handful of cases actually sequenced by the ESR were reported to be BA.5. In the week ended June 21, it was 11% of the cases in the sample.

dr David Welch, a senior lecturer and Covid-19 modeler at the University of Auckland, has told it Things if this trend continues, BA.5 could hit 50% as early as mid-July.

The daily case numbers have also ticked up. On June 25, the 7-day moving average was 4820. On Monday, July 4, it was 7227.

BA.5 appears to be taking off in New Zealand.

Ella Bates-Hermans/Stuff

BA.5 appears to be taking off in New Zealand.

What drives all this?

A few things. First, it’s winter, which means we’re spending more time indoors, which allows viruses to spread better. second, the protection – or antibodies – provided by vaccination, and indeed the infection, wears off. This was expected. And finally, BA.5’s characteristics mean that it’s very good at dodging this immunity.

When it comes to BA.4 and BA.5, their “superpower is reinfection,” said Dr. Peter Chin-Hong, an infectious disease expert at UC San Francisco, recently LA times.

As the American Covid expert Professor Eric Topol recently explained in a blog post, the risk of reinfection has increased significantly for two reasons. First, BA.1 induces or effects a “fairly tight” immune response that doesn’t offer as much protection against BA.4 or BA.5.

And BA.5’s spike protein — the part of the virus that antibodies target — is quite unique, meaning it’s quite capable of forcing its way into our systems.

So this wave will only consist of reinfections?

Not necessarily, says Professor Michael Plank. There are still people out there, particularly in older age groups, who haven’t had Covid. You’re probably infected now, which is worrying.

“The number of people who have not yet had Covid can be relatively small in younger age groups. In older groups, however, the number of cases was much lower, so there are still more people to be infected in these groups.

“It’s likely that those who haven’t had Covid are at a higher risk of getting it in the next wave.”


Yes, as Plank points out, the daily number of cases among those over 70 is higher than ever before. This is bad news as older people are most at risk from this virus.

How bad will it get?

It’s hard to know for sure. It’s possible we’ll see case numbers comparable to March (over 20,000), but that depends on people actually uploading their case results.

The number of people in hospital with Covid has already increased. But remember, if more people have Covid, more will end up in hospital with Covid for completely different reasons. However, more Covid means more very sick people, especially in older age groups.

There’s hope that the high level of immunity in New Zealand, boosted in part by all those BA.2 infections (hybrid immunity), can help keep the hospitalization rate down, says Plank.

However, if the virus infects another population group – ie older people who have not previously been infected – there is a risk that the hospital admission rate will actually increase.

Paradoxically, this could mean the second wave sees fewer cases but causes a greater health burden – or sends more people to the hospital. We will see.

Good news is that there is no evidence BA.5 is any more severe in humans than the other Omicron variants.

Wait, you mentioned we had a lot of BA.2? Won’t that help?

Yes, let’s dwell on this point for a moment. The Covid vaccines and infections produce an immune response. There are antibodies, or your first line of defense against infection, but the body also pumps out B and T cells. These are more robust and durable and protect against serious illnesses.

I asked Paul Hunter, Professor of Medicine at the University of East Anglia, if all these BA.2 infections would provide some sort of barrier to BA.5. As I mentioned above, BA.2 is more like BA.5 than BA.1

In his view, it’s still too early to know exactly how much mutual protection there would be between BA.2 and BA.5, but there should at least be a barrier against infection.

Then what about serious illness? “The evidence at this point is that the cross-protection against major diseases is quite stronger from each of the variants. So it’s likely that even if cross-immunity from infection isn’t as good, we’re still getting cross-protection from serious diseases.”

We’ve seen this throughout the pandemic. Immunity to serious diseases, especially in those who have been vaccinated and infected, is holding up very well.


Yes, all that hybrid immunity should help. But there is a big “but”.

“Unfortunately, levels of hybrid immunity are lowest in the most vulnerable groups (older people) because they weren’t hit as hard as younger groups by the March wave,” says Plank.

He also points out that while BA.2 is closer to BA.5 than the first iteration of Omicron, countries that had a big BA.2 wave had, or still have, a surge in BA.5 cases . Bottom line, all that BA.2 is probably not a card to get out of jail.

Sure, but a second infection wouldn’t be so bad for me, would it?

A recent paper caused a stir on social media as it seemed to suggest co-infections were more serious in Covid patients. Without getting into the weeds, that’s not necessarily the case. As Plank points out, the study simply wasn’t designed to compare the severity of a first infection to a second.

And as Ben Krishna, a postdoctoral researcher in immunology and virology at the University of Cambridge, pointed out in a recent article for The Conversation, scientists have generally found that reinfections are less severe than initial infections.

Yes, there will be people for whom the second infection is worse, and you’ll likely read a lot of these stories in the coming weeks, but across the population, reinfections shouldn’t be as acute.

Hunter explains: “We’ve seen in the UK that secondary infections show up much less frequently in daily dashboard figures than primary infections, mainly because people tend to be less ill enough to believe they need a test.”

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