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BA.4 and BA.5 in South Africa, another one in the USA: SRF science editor Katrin Zöfel on the most important questions.
How do subvariants BA.2.12.1 (USA) and BA.4 and BA.5 (South Africa) differ from earlier omicron subvariants? Altogether there are now five sub-variants of Omicron, which give something to talk about. The “first” Omicron was BA.1, then BA.2, which is currently dominant in Switzerland. And now BA.2.12.1, which is spreading especially in the US, and BA.4. and BA.5, which are known to be spreading in South Africa and increasing the number of cases there. BA.2 was already able to assert itself against BA.1, it has almost completely replaced BA.1 in Switzerland, mainly because it was more contagious. BA.2.12.1, BA.4 and BA.5 now carry further, different mutations in the spike protein, which apparently give the virus advantages.
BA.2.12.1, So BA.4 and BA.5 are more contagious than previous Omicron variants. But do they also make you more ill? So far there is little evidence of this. Very many, if not all, of the infections with the new subvariants are reinfections or breakthrough infections, which is why this question cannot be answered very clearly because one can no longer observe any “virgin” infections without pre-existing immunity, so to speak. At the same time, this is also the reason why many experts do not expect hospitalizations to increase very sharply, even if the number of cases should now increase again: precisely because the immunity that has already been acquired protects.
How well do the existing vaccines or past infection protect against BA.2.12.1, BA.4 and BA.5? As always in the pandemic, the knowledge about this is only just being acquired. study results suggest, however, that triple vaccination still offers good protection against omicron and its subvariants, not necessarily against infection but against severe courses. Infection with BA.1 alone (the “first” omicron) results in Laboratory data from South Africa on the other hand, little protection against BA.4 and BA.5.
Why are there so many subvariants of omicron? Delta, for example, has had fewer sub-variants that have achieved some notoriety, that’s true. Omicron very quickly and almost completely replaced Delta and Omicron has been dominating the infection process for quite some time now: Almost all infections worldwide can be traced back to Omicron and its subvariants. Omicron also bypasses acquired immunity even more effectively than Delta, so it can reinfect people who already had immunity. As a result, this means: Omicron gets an infinite number of chances to infect people, to mutate in the process and to form new sub-variants over and over again.
The variants BA.4 and BA.5 have also been detected in Switzerland. How common are they? They are still rare. BA.2 still dominates here. (Here is an overview of the global distribution of the BA.4 and BA.5 variants).
Can one draw conclusions about Switzerland from developments in the USA and South Africa? Do we also have to expect an increase in infections in this country? You can only make limited predictions for Switzerland based on what is happening in other countries. But one can deduce what is worth keeping an eye on. Experts in Australia, where BA.2 dominates, as in Switzerland, and where BA.4, BA.5 and BA.2.12.1 have only been detected a few times, expect increasing numbers of infections because they expect many reinfections (click here for study). It is also clear that the immunity of the population will decrease over time and that the weather conditions will favor infections again in the autumn. You also have to reckon with the fact that sub-variants of Omikron or even completely new variants will continue to develop.