Analysis of BA.5 versus previous Omicron subvariants

Disease and treatment 1. sep 2022 2 min Assistant Professor Christian Holm Hansen Written by Kristian Sjøgren

A preliminary analysis of COVID-19 cases in Denmark shows that the new Omicron subvariant BA.5 shares many of the same illness characteristics as previous variants. Previous infection with an Omicron subvariant seems to offer good protection against BA.5, and vaccines appear to be just as effective against BA.5 as for previous Omicron subvariants. Nevertheless, BA.5 infection is associated with an increased risk of hospitalisation.

A new Omicron subvariant, BA.5, emerged in spring 2022. First discovered in South Africa, BA.5 then spread to southern Europe and the rest of the world.

Doctors and health authorities globally are following the spread of BA.5, and researchers in Denmark have carried out one of the first analyses of this subvariant compared with previous Omicron subvariants.

A review of people testing positive for BA.5 in Denmark between 10 April and 20 June 2022 reveals that BA.5 is associated with a slightly more serious illness trajectory, as shown by the proportion who are hospitalised.

Nevertheless, the new study also shows that vaccines apparently protect just as well against BA.5 as against the BA.1 and BA.2 Omicron subvariants. In addition, the good news is that people previously infected with BA.1 or BA.2 are very well protected against BA.5.

“This is a very good sign that previous infection protects against BA.5. Since many people in Denmark have been infected with one of the previous subvariants, this may well protect against a large wave of infection,” explains a researcher behind the study, Christian Holm Hansen, Department of Infectious Disease Epidemiology and Prevention, Statens Serum Institut, Copenhagen, Denmark.

The research, which is pending peer review, has been published is The Lancet Infectious Diseases.

Previous infection protects against BA.5

The researchers reviewed all the SARS-CoV-2 test data in Denmark for 10 April to 20 June 2022: 4,809 triple-vaccinated cases who tested positive for SARS-CoV-2 with a BA.5 infection and 164,369 individuals testing negative.

The researchers carried out three analyses. The first determined how previous infection with an Omicron variant protects against BA.5 infection by comparing the proportion of cases testing positive for BA.5 and test-negative controls with previous Omicron infection.

The results showed very clearly that previous infection with BA.1 or BA.2 protects against infection with BA.5.

“If you have previously been infected with an Omicron variant, you are about 94% protected against infection with BA.5, which is a really good level of protection,” says Christian Holm Hansen.

Vaccine protection has not declined

The second analysis examined whether vaccination against SARS-CoV-2 protects as well against BA.5 as against earlier Omicron subvariants.

During the study period, both the BA.2 and BA.5 Omicron subvariants flourished, so the researchers analysed only the people infected with BA.5 or BA.2. They identified any difference in the proportion of these who were vaccinated, depending on which subvariant a person was infected with.

The researchers found no difference in the proportion of triple-vaccinated individuals among those infected with BA.2 versus BA.5. Christian Holm Hansen sees this as a sign that vaccination protects equally well against both subvariants.

“We cannot say how well you are protected against infection with BA.5 if you are triple-vaccinated. But we can say that you are apparently just as well protected against BA.5 as against BA.2,” he explains.

Hospitalisation more likely with BA.5

Finally, the researchers analysed the severity of BA.5 infection and whether this resulted in a more serious illness trajectory and hospitalisation.

The other two analyses are positive, but this result points in a negative direction. The data indicate that infection with BA.5 is associated with an approximately 65% increased risk of hospitalisation compared with infection with another Omicron subvariant.

Nevertheless, Christian Holm Hansen says that more studies must substantiate this finding before it can be fully confirmed.

“We also want to see the pattern in other countries. Remember that this is not a clinically controlled study, but observational data, so we should be cautious about conclusions,” he says.

The data are being followed globally

According to Christian Holm Hansen, there is great interest in the data from Denmark.

One reason is that, throughout the COVID-19 pandemic, Denmark has been good at integrating real-world health data, epidemiological research, laboratory capacity and bioinformatics. Thus , the researchers from Statens Serum Institut can be a source of information on how the new SARS-CoV-2 variants will affect Denmark and the rest of the world.

“The results indicate that many people in Denmark are well protected against BA.5, since many have already been infected with previous Omicron subvariants, and vaccination coverage in Denmark is also very high. This may mean that the wave of infection will not be as serious in the autumn as it could have been had we found poorer protection from vaccination and previous infection. How hard the BA.5 wave hits around the world will therefore probably also depend greatly on the level of population immunity in the relevant places,” concludes Christian Holm Hansen.

Risk of reinfection, vaccine protection, and severity of infection with the BA.5 Omicron subvariant: a Danish nation-wide population-based study” has been been published in The Lancet Infectious Diseases. The research builds on the data from TestCenter Danmark, which was established under Statens Serum Institut in close collaboration between the Danish state, the administrative regions, the national emergency services and hospitals, including Rigshospitalet, as well as the Novo Nordisk Foundation and the pharmaceutical company Novo Nordisk A/S.

Christian is a medical statistician and epidemiologist with Statens Serum Institut (SSI) in Denmark and the London School of Hygiene and Tropical Medi...

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