Yet another covid-19 wave is beginning in Australia, the US and parts of Europe, among other places. Driven by two omicron subvariants, called BA.4 and BA.5, experts are unsure how bad it will be.
There is some evidence that BA.5 in particular may cause more severe disease than its predecessors BA.2 and BA.1, but there is also high covid-19 immunity in most populations.
鈥淎ll I can safely say is that Australia, the US and UK appear to be on track for BA.5 to dominate,鈥� says at the University of New South Wales in Australia.
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The term 鈥渙micron鈥� applies to a family of variants discovered in southern Africa in November 2021. All omicron variants differ from earlier SARS-CoV-2 variants by around 50 mutations, making them more contagious and better at evading prior immunity.
BA.1 caused a massive wave of cases, first in South Africa, before spreading worldwide from December 2021. In March, before the BA.1 wave ended, BA.2 started taking over, causing a second wave in some places.
While the reported number of BA.1 and BA.2 cases was much higher than covid-19 incidences in previous waves, many countries reported far fewer deaths. This was due to widespread immunity from vaccinations and past infections, as well as BA.1 and BA.2 than the delta variant that preceded them.
However, some countries that previously managed to prevent large outbreaks, such as South Korea, were less successful at containing the highly contagious BA.1 and BA.2, leading to a higher number of deaths. In Hong Kong, covid-19 deaths soared to their highest reported rate, driven by high case numbers, low vaccination levels among older people and hospitals being overwhelmed. China is still battling to maintain its zero-covid policy, with being reported soon after Shanghai eased restrictions.
And the BA.2 wave isn鈥檛 over in some places. In England, the number of reported cases has plummeted, not just because of falling infections but also because of reduced testing. Surveys by the Office for National Statistics, which give a more accurate picture, show that levels are still relatively high, with at the beginning of June.
BA.4 and BA.5 mean cases are starting to increase in the UK and elsewhere. While these differ from other omicron subvariants by only a few mutations, and other groups suggest BA.4 and BA.5 are even more contagious and better at evading antibodies in vaccinated people or those who have had BA.1 or BA.2.
What鈥檚 more, a study published on 14 June found that , suggesting that many people could get BA.4 and BA.5 even if they had BA.1 or BA.2.
Perhaps more concerningly, Sato found that BA.4 and BA.5 were more likely to cause severe disease than BA.2 in a hamster study.
BA.1 and BA.2 enter cells in a different way to delta, making them less likely to infect lung cells, which may be why they cause milder symptoms. But according to initial results from Turville鈥檚 team, BA.5 has switched back to entering cells in the same way as delta. 鈥淎ll of this is very early, but there is a signal,鈥� says Turville.
However, this than BA.1 or BA.2, as most people have at least some covid-19 immunity. 鈥淎s for disease severity, we are dealing with various layers of immunity and that question is far more complex now than, say, in 2020,鈥� says Turville.
South Africa has already had a BA.4 and BA.5 wave, which was . However, Portugal, the first country in Europe to have a BA.5 wave, has seen hospitalisations and deaths they reached during the peak of the country鈥檚 BA.1 wave.
Why Portugal is faring worse than South Africa is unclear. Immunity from past waves or vaccinations, as well as the age of the population, could all play a role, says Turville.
Another factor could be the previous proportion of BA.2 infections, which may against BA.4 and BA.5. Some countries, such as the UK, had bigger BA.2 waves than Portugal, and so may be in a better position for BA.4 and BA.5, says at University College London.
China, however, may still be especially vulnerable. Despite efforts to boost vaccination levels, had received three doses by 2 June, compared with . What鈥檚 more, the vaccines used in China may be less effective.
For now, countries should monitor what is happening and focus on vaccinating anyone who hasn鈥檛 had at least three doses, the European Centre for Disease Prevention and Control .
People may also want to consider what measures they can take, such as wearing masks or reducing socialisation, says Pagel, who also encourages improving ventilation in buildings.
This long-term measure won鈥檛 stop new covid-19 waves, but could reduce their impact, she says. 鈥淓ach of [the waves] do come with some attrition, some death, and also long covid is increasingly becoming an issue.鈥�
