FuuuuUuuUUuUuck. Another strain of COVID-19, the BA.4 subvariant of Omicron, has reached Australia and I am feeling emotionally strained by this news.

The first local case of BA.4 was reported by NSW health authorities on Thursday following a spike in both BA.4 and BA.5 subvariants in South Africa.

The World Health Organisation said it was monitoring BA.4 and BA.5, which have several new mutations. Experts said this meant the chances of COVID reinfection in Australia could rise.

While millions of Aussies have had COVID, far fewer have had it twice. But the more variants and subvariants transmit throughout our community the more likely reinfection becomes because your body’s defence systems are less likely to recognise a new version of the virus than one it’s already fought off.

“We are going to see new subvariants causing increased transmission in Australia within the next couple of months,” associate professor at UNSW’s School of Public Health and Community Medicine James Wood told the Sydney Morning Herald.

“BA.4 and BA.5 in South Africa are clearly causing cases to go up, and we can expect these are already here in low numbers”.

To be clear, this isn’t a new variant. BA.4 and BA.5 have been around since Omicron was first detected in November 2021. The nickname Omicron refers to the family of subvariants or sublineages — the main ones are BA.1, BA.2 and BA.3, but 4 and 5 and spreading because each has some different mutations. BA.1 spread around the world late last year and as time goes on others will too.

Delta, for example, has more than 200 sublineages and experts say no doubt more Omicron sublineages will be described in future.

We don’t know exactly how many people have been reinfected with COVID in Australia but in Victoria it was at least 10,000 between December and March. NSW health has not reported reinfection numbers but they’ll no doubt be higher.

But it’s not all bad news. The theory is that each reinfection will have milder symptoms than the last which will eventually downgrade the pandemic to be endemic to certain areas rather than covering the whole globe.

“Reinfections will become the norm but what we hope is repeat infections will be milder each time as natural immunity combined with vaccination generates strong protection,” epidemiologist James McCaw told the SMH.

McCaw said COVID-19 was on the “path to endemicity” thanks to vaccines.

He noted that vaccines likely still offered very strong protection against BA.4 as they have every other variant and subvariant. COVID will likely stick around long into the future, but its severity should wane over time as people’s immunity strengthens.