The BA.5 Omicron variant – now dominant in the UK – is more than three times as likely to put you in hospital than its predecessor BA.2, a new study suggest.
Portugese researchers found that people who had been vaccinated and boosted had a 7 per cent risk of hospitalisation from BA.2, rising to 23 per cent with BA.5 – suggesting they are 3.3 times more at risk.
However, experts cautioned that it was too early to draw any firm conclusions about the hospitalisation risk posed by BA.5.
Another new study, from Denmark, for example saw a lower disparity between the two subvariants – finding the risk of hospitalisation by BA.5 to be 1.65 times higher than for BA.2.
“BA.5 cases vaccinated with booster had more than three times higher odds of hospitalisation compared to BA.2 cases,” said Irina Kislaya, of the National Institute of Health in Lisbon, who worked on the Portugese study.
This was published on the Medrxiv preprint server, ahead of peer review, due to its timely nature.
“Our results suggest that higher immune evasion of BA.5 might explain the surge in cases seen in countries
with high BA.5 prevalence,” she said.
“The Omicron BA.5 lineage is associated with higher odds of reinfection compared with Omicron BA.2, regardless of the vaccination status,” but vaccination provides extremely good protection against severe illness for both subvariants, she says.
“Our study suggests similar vaccine effectiveness against infection with BA.5 compared to BA.2,” Dr Kislaya said.
Christian Holm Hansen, of the Statens Serum Institut, who worked on the Danish study, added: “BA.5 infection was associated with an increased risk of hospitalisation”.
However, he cautioned that the findings “need confirmation and continued surveillance as hospitalisations were low and stable during the study period”.
Professor Paul Hunter, of University of East Anglia, echoes this caution.
He points out that these studies may be significantly exaggerating the risk of BA.5 on the basis that far fewer cases, in proportionate terms, are being diagnosed under BA.5’s dominance than they were when BA.2 and earlier variants were dominant.
This is due to factors such as the ending of free tests and symptoms becoming milder.
Since people are now less likely to be tested, especially when symptoms are mild, the less serious cases are less likely to be diagnosed.
As a result, those cases that are diagnosed are likely to be the more serious ones and so more likely to result in hospitalisation – giving a higher proportion of hospitalisations – while thousands of milder cases go undetected and are not included in the hospitalisation ratio calculations, he says.
The trend towards reduced testing is underlined by the fact when the Portugese study began, in late April, one in four people who tested were testing positive. This had fallen to one in two when it ended in mid June. BA.5 became dominant in Portugal in late May.
Professor Hunter has done his own calculations and concluded that “it doesn’t look like we will see a much higher hospitalisation rate than we saw with BA.2, but some increase is still possible”.
“This isn’t to say BA.5 is associated with an increased risk of hospitalisation – but it’s early days yet,” he says.
Professor Hunter notes, in relation to his own work and the other studies, that “we need to wait till end of BA.5 wave to be certain” of the relative hospitalisation risk of BA.5 and BA.2.
However, experts agree that, whatever the precise hospitalisation risk of BA.5 turns out to be, it is likely to be considerably lower than it was during previous peaks – before vaccines were available and during the period when Delta, a much more severe subvariant than BA.5, was dominant.
So although daily symptomatic cases in the UK are predicted to go as high as 650,000 a day in late Autumn – compared to the previous record of 351.546 – according to the ZOE Covid Study app – hospitalisations will still be well below the record level seen in January 2021, when more than 4,000 people a day were admitted to hospital and the second highest peak, in April 2020, when they reached 3,000.
But they are likely to be higher than any of the peaks seen so far this year – of 2,000 to 2,500 a day – due to the much higher number of cases expected, experts said.
Professor Karl Friston, a virus modeller at University College London, said: “The number of hospitalisations will depend not just upon the pathogenicity of BA.5, relative to other variants and strains, it will depend on the prevalence of infection, which will be high during the autumn.”
“Current estimates suggests the daily deaths next winter will be comparable with last winter (peaking at about 200 per day). On one view, this is unacceptably high and a lamentable way of “living with COVID”. On the other hand, these will be less than the death rates seen during the first two waves,” he said.
This is all assuming that BA.5 remains the dominant variant during the Autumn wave, however. If another Omicron subvariant – or new variant – comes along then hospitalisation numbers could be far higher, or far lower, depending on how severe it is, experts said.