Today’s missive is somewhat shorter as I thought it would be useful to focus just on what Pi may look like – Pi is the next letter in the Greek alphabet after omicron and is likely to be the name of the next variant of concern.
1.The epidemic in South Africa
The epidemic in South Africa is behaving exactly as expected (Slide 1). At this point after each of the past 3 waves, cases had come down to about 1,000 per day and have stayed low for the approximately 3-month inter-wave period (Slide 2). This pattern is being followed well after the 4th wave in South Africa.
Globally, the post-BA.1 omicron blip caused mostly by BA.2 has settled just as it had done in South Africa and cases are now back on the decline (Slide 5). So, the question is: Is this the lull before the next storm? (Note that some countries like Hong Kong and China are still dealing with the tail-end of the previous omicron storm). Or has SARS-CoV-2 reached it zenith in terms of mutations that confer an advantage (Slide 6). While I am hoping for the latter, I am expecting the former and that the current lull will likely be shattered in about a month’s time in South Africa. But for this to happen, there has to be a new variant!
3.What to expect in Pi?
Omicron generates quite good immunity to itself and to Delta and so viruses that share antigenic structure with these 2 viruses may have difficulty escaping immunity. But the 2 new variants that have been reported to be spreading are BA.4 and Deltacron. BA.4 seems to be a recombination of BA.1 and BA.3 plus some additional mutations – it has been found in a few countries though several of the BA.4 sequences come from South Africa (Slide 8). Similarly, Deltacron has been reported from several countries but it does not seem to have the ability to become a fully fledged variant of concern. Should we worry about these 2 seeming recombination viruses of omicron? I don’t think so as they share quite a bit of their antigenic structure with omicron and so it may not find it easy to infect people with past omicron infection or those with vaccine immunity.
So, we are more likely to see a different variant become Pi. What are some of the characteristics of Pi that we can expect? It will have to be more transmissible – if it isn’t, it will not be able to out-compete and replace omicron. Even if a variant has some immune escape but is not more transmissible, it is not likely to become Pi (Slide 9). This modelling approach suggests that transmissibility trumps all else. The virulence and the severity of Pi will be dependent on viral characteristics and immunity (vaccine & natural immunity) and is more difficult to predict as the mutations that confer disease severity are not understood.
So, enjoy the next few weeks of low transmission across most countries in the world, just in case it does not last much beyond early May (Slide 10). Statistically, the UK is most likely to discover the next variant because it does the most sequencing, has high levels of viral transmission, has lots of people visiting from all over the world and has very few restrictions to lower viral transmission.
Salim S. Abdool Karim, FRS
CAPRISA Professor of Global Health: Columbia University