#16,905
The BA.5 Omicron subvariant which has taken the world by storm the past couple of months continues to drive up hospitalization rates, but it remains uncertain whether that rise due to the sheer number of new infections, or to some uptick in its severity over BA.2.
At least, until now.
Today Denmark's SSI has published a summary of a recent preprint, authored in house, which finds a modest increase (16% to 124% (95% confidence interval)) in the severity of BA.5 (based on an increased risk of hospitalization) over BA.2.
This is just one study, confined to a single country, so confirmatory data from other sources will be needed before we can say anything with confidence.
This study also looked at the protection provided by previous infection, vaccination - and both - against reinfection by BA.5. Having the combination of a previous Omicron infection, along with being triple-jabbed, provides the best protection (94%) according to their findings.
For those (like myself) who were infected in 2021 with Alpha or Delta - but who escaped Omicron - the combined protection falls markedly. The authors write:
By comparison, a previous delta or alpha infection provided much weaker protection of 46.9% (27.0 to 61.3%) and 65.4% (49.8 to 76.2%) respectively, against a new infection with BA.5.
The translated summary from the SSI follows, along with a link to the preprint.
Previous infection with omicron together with 3 plugs effectively protects against infection with the omicron variant BA.5
A new study from the Statens Serum Institut shows that you are well protected against infection with the current dominant omicron variant BA.5 if you have previously been infected with an omicron variant and have received three vaccine injections.Last edited on 27 July 2022
The study, which has been submitted for peer review, thus shows that previous omicron infection protects 94% against BA.5 if you are simultaneously vaccinated with three vaccine doses with either Pfizer-BioNTech or Moderna.
Previous infection with omicron variant protects against BA.5
The study includes 4,809 people infected with the omicron variant BA.5, and 164,369 control people who tested negative for SARS-CoV-2 in the period 10 April to 20 June 2022.
The study investigated how many of those infected with BA.5 had also previously had an infection with an omicron variant in January 2022 and compared this with how many control subjects had had an infection with omicron in January 2022.
The study thus found that people who have had an omicron infection in January 2022 and are vaccinated with 3 shots have a protection of 94% against BA.5.
The results must be seen in the light of the fact that 75% of the population over 18 years of age, which the study examines, has been vaccinated with 3 shots, and that a third of the population has presumably already had an omicron infection before March 2022.
Vaccine efficacy and severity for BA.5 compared with BA.2
The study has also investigated whether three vaccine doses work equally effectively against BA.5 as against BA.2, and whether there is a higher risk of those infected with BA.5 being hospitalized compared to those infected with BA.2.
In the analysis, the approx. 5,000 people infected with BA.5 with approx. 32,000 BA.2 infected in the same period. The analysis shows that the vaccines protect just as well against infection with BA.5 as they currently do against BA.2. The analysis of hospitalization risk shows that, when age and period of infection are taken into account, BA.5 leads to relatively more hospitalizations than BA.2.
Relative to BA.2, there is thus an increased risk of being hospitalized due to BA.5 in the order of 16% to 124% (95% confidence interval), which indicates that the variant is more serious.
This is not immediately worrying, as the number of hospitalizations, intensive care units, or deaths due to covid-19 is still at a low level, compared to the omicron wave of the winter.
At the same time, the analysis confirms that the omicron variants lead to considerably milder disease courses than delta – the most serious of the other covid-19 variants so far. The Statens Serum Institut is following developments closely.
The study has been submitted for peer review at an international scientific journal, and in the meantime published as a preprint here.
Hansen, Christian Holm and Friis, Nikolaj Ulrik and Bager, Peter and Stegger, Marc and Fonager, Jannik and Fomsgaard, Anders and Gram, Mie Agermose and Engbo Christiansen, Lasse and Ethelberg, Steen and Legarth, Rebecca and Grove Krause, Tyra and Ullum, Henrik and Valentiner-Branth, Palle, Risk of Reinfection, Vaccine Protection, and Severity of Infection with the BA.5 Omicron Subvariant: A Danish Nation-Wide Population-Based Study. Available at SSRN: https://ssrn.com/abstract=4165630 or http://dx.doi.org/10.2139/ssrn.4165630
