The BA.4 and BA.5 coronavirus subvariants now driving waves of infections in many countries are the most contagious yet – mostly due to mutations that allow them to dodge our immune defences. The good news, though, is that there is still plenty you can do to reduce your risk of infection.
Over the past two weeks, global cases of covid-19 have increased by , largely due to omicron subvariants BA.4 and BA.5, according to the World Health Organization (WHO).
Since the subvariants were first identified in South Africa in January, they have been seen throughout the globe, triggering a new wave of covid-19 cases in the UK, Australia, Germany, Portugal, France, Panama, Japan and elsewhere. In the US, BA.4 and BA.5 now account for .
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“We know that these strains have the highest transmission potential — they’re the most contagious,” says at New York University Langone Health.
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Most contagious yet
There are two reasons for that. First, BA.4 and BA.5 have mutations that , meaning an infected person is more likely to pass on the virus.
Second, and what makes BA.4 and BA.5 so infectious compared to past, already highly transmissible omicron subvariants, is how well they can dodge our immune systems. “They have the most significant immune evasion compared to any other prior strain,” says Lighter.
That is due to multiple genetic mutations, some of which occur on the spike protein. This protein helps the virus latch onto and infect cells. It is also the part vaccines target.
Changes in the spike protein make it more difficult for vaccine-induced antibodies to recognise and then kill the SARS-CoV-2 virus, says at the Cincinnati Children’s Hospital Medical Center in Ohio. Early evidence indicates to antibodies from vaccinated and boosted individuals than the earlier omicron subvariant BA.2, which spread through the US and Europe in the spring.
This means covid-19 cases are becoming more common in vaccinated people and even those with a recent infection. But there are still ways to protect yourself.
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Vaccines remain crucial
Frenck and Lighter both say that vaccination remains the best way to reduce your risk of infection and severe disease. Less than of people aged 12 and older have had three covid-19 vaccine shots in England, and just of people aged 5 and older have done so in the US, despite the fact that boosters are more than at preventing hospitalisation and death in breakthrough omicron infections. Even if that number is a bit less with BA.4 and BA.5, it is still likely to provide a significant benefit, they say.
Additionally, a preliminary study from South Africa found that antibodies from vaccinated individuals who had previously had covid-19 were and BA.4 than antibodies from unvaccinated people with a previous infection. The study assessed antibody samples from 39 people — 15 of whom were vaccinated — who had recently been infected with BA.1, an earlier omicron subvariant.
“That’s why we’re still advocating, even if you’ve been infected, and even if you’ve been infected with omicron, to go get vaccinated,” says Frenck.
In the US, the currently recommends that people aged 5 years and older should get one booster. Adults aged 50 and older and people who are immunocompromised should have two boosters.
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Outdoor transmission
There is also good news for those who are already up to date on their vaccines but want further protection: previous measures — like socialising outdoors and masking — still reduce risk of infection with the newer subvariants.
We know that omicron subvariants in an infected person, meaning that person will emit more viral particles when they sneeze than someone with another variant like delta would, for instance. With more infectious particles, there is a higher likelihood that some will sneak through masks, particularly ill-fitting ones. For more protection in indoor settings, people may want to consider upgrading to masks that are tighter on the face, like an N95, says Lighter.
As for socialising outside, there have been reports that meeting up outdoors is much riskier with BA.4 and BA.5 in circulation. That isn’t true, says Lighter. While there is always a risk of infection outdoors — even with past variants — it is still significantly lower than the risk of socialising indoors. That is because fresh air is constantly moving, which breaks up respiratory droplets carrying the virus so you are less likely to inhale them.
No matter how good a virus is at evading immunity, wind currents will still disperse particles and masks will still trap sneezes and coughs, says Frenck. The method of transmission – inhaling airborne particles – hasn’t changed. “Anything that can get through a mask from the original variant is anything that can get through from BA.5,” he says. “There is no change in size of virus particle or anything like that.”
There is also little evidence to suggest that symptoms or compared with previous omicron subvariants, says Lighter. That doesn’t mean they are harmless, of course. All covid-19 variants pose risk of serious illness or complications like long covid, which is why it is important to protect yourself.
“Your best bet is the vaccine,” says Frenck.
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Article amended on 18 July 2022
We clarified what proportion of the population in England and the US has had three covid-19 vaccine shots.
