Omicron 2, what do we know about the BA.2 variant

BA.2 is a sub-lineage of BA.1, i.e. a kind of “different twin” variant of the Omicron, also journalistically baptized Omicron 2. Growing in some European countries – in Denmark it even ousted Omicron, reaching over 65% of the samples – and in Asia, also present in Italy, it differs in some mutations and in some characteristics from BA.1. Let’s see which ones.

Omicron’s three sub-lineages – BA.1, BA.2 and BA.3 – appear to have emerged more or less simultaneously, around last November. The first sequences were uploaded to Gisaid, the international portal dedicated to tracing variants on an international scale, from South Africa and the Philippines. While, as we said, Denmark – which has an excellent sequencing system – has uploaded the highest number of them in recent weeks. Everything suggests that they had time to differentiate before the Omicron wave in December and therefore that BA.2 is not the result of a subsequent evolution.

Some experts have even renamed it invisible variant, although this label has only led to misunderstandings and is to be abandoned. It refers to the fact that, not having the typical Omicron BA.1 deletion of the S gene, the variant is undoubtedly identified by an antigenic or molecular test but there is no longer an element of rapid confirmation that suggests to us with some certainty that it is BA.2, as it happens instead with the other lineage. In short, it is necessary to sequence the sample while with the Omicron BA.1 the absence of the S gene from the tests comes to our aid.

Some important data are obtained from a Danish study still awaiting peer-review. For example, that the stump would appear more contagious than BA.1 – which was already the most transmissible pathogen in recent history – and also more capable of evading the defenses determined by vaccination. But what about the vaccines however, they remain very protective against the severe form of Covid-19 and therefore against death. Not only that: when the positive in a family has received two or three doses, transmissibility does not increase.

Anders Fomsgaard, virologist of the Danish State Serum Institute, had in fact declared – as reported by Corriere della Sera – that it now represents about 65% of new cases: “We are not that worried, since so far we do not see large differences in the distribution by age, vaccination status, reinfection and risk of hospitalization. Furthermore, despite the high rate of BA.2 infection, the number of ICU admissions is decreasing. The Danish Minister of Health, Magnus Heunicke, added that “there is no evidence that the BA.2 variant causes more severe disease, but it must be more contagious“. The aforementioned study calculated that Omicron 2 would have a secondary attack rate, i.e. the number of infections that occur in a given time window and in a small population, of 39% while that of BA.1 stands at 29%. And, as the Copenhagen authorities said, there was also greater transmissibility from unvaccinated primary cases in their own families, but not in households where the Omicron 2 positives had 2 or 3 doses. In short, vaccinating remains fundamental even against the new variant which, as we said, is not new.

The attack rate is not an incidence: it is an indicator that gives us an idea of ​​what happened for a defined and limited time. In short, even if the observation period were prolonged, no new cases would be observed. In the case of BA.2 it would appear 10% higher than Omicron.