Bert Mulder, a Nijmegen medical microbiologist whom I sometimes speak to, is not very good at it. Only a month and a half ago it was delta, which was the clock. And now, suddenly: omikron everywhere. ‘So I find that fascinating. But also insane, and almost incomprehensible’, he reflects on the phone. ‘Where has the delta variant suddenly gone? Such a virus cannot suddenly disappear completely, can it?’
It’s a question that more people have. ‘I would think that different variants could coexist’, writes Guido Bos from Voorhout. ‘But then I read: omikron has taken over delta.’
Well, how does that work exactly? Will delta be chased out of the country or something? Or are the delta viruses eaten by the newcomer, or absorbed, or how do viruses do that?
Well no. The answer is simple, yet so counterintuitive that many people are confused: it’s just evolution. ‘If one variant takes over from the other, that simply means that that variant infects more people per day,’ says evolutionary biologist Tom Wenseleers (KU Leuven) on the phone when asked.
That can be for several reasons. In other words, the new virus has a trick that makes it easier for it to enter cells. In other words, he can escape from antibodies, so that he can also infect people who were actually already immune. Either the newcomer has a faster reproductive time. More, more invisible, faster: omikron seems to have those last two properties in particular. ‘These are important advantages’, says Wenseleers.
And then leave the replacement to that wondrous phenomenon that makes diseases run wild, fills ponds with duckweed, and makes whole clouds suddenly appear from a few fruit flies in the kitchen: ‘exponential growth’. The new variant does not increase as one intuitively imagines, step by step or linearly – but at an ever faster pace, with a multiplication factor, like a gas pedal that you press deeper and deeper.
To get a feel for it, I do some puzzling on a scrap of paper. Take two viruses: the Sloompie variant, which is already circulating everywhere and infects three people every three days, and the Kwik variant, which is newly added and infects four people every three days.
It may take a while before Mercury dominates the entire country, you think by feel. But no. After less than two months, Mercury is in the majority. And after another more than a month, Sloompie has become a rarity, with Mercury making up more than 98 percent of infections. After which Sloompie literally cannot find any more fresh hosts – and dies.
That’s how it really goes. In our country it took more than three months before the ‘British variant’ alpha caused almost all infections; the alpha variant has not been observed in any sample since September. And in the most recent sample, in mid-January, only 23 units of the delta variant, which until recently ruled the world, were found – and 1,245 omikrons.
In the meantime, omikron has found its own Mercury again, in the guise of BA.2. At the last count in the test line, it made up 4 percent of the total. And before you say: that’s not too bad, think of the exponential growth. About five or six weeks, and it’s only BA.2 that counts.
This does not mean, however, that the old variants will disappear completely, Wenseleers believes. ‘Often the variant will continue to circulate somewhere, in very low numbers, out of sight. Such a virus has then jumped to another host, an animal or something. Or he hides in an isolated community, or with immunocompromised patients, people with a latent, chronic infection.’
It’s tempting to see those viruses as vulnerable animal species in a jungle, some of which are rare, withering and dying out — like that’s pathetic, or something. But of course it isn’t. Rather, such a virus is a swirling cloud, constantly in motion, with bulges that arise and disappear, vortices that come and go, sub-clouds that split off and merge into the whole again.
The virus does not think, does not feel, does not realize. Does the virus care that a variant disappears now and then? Alpha, delta, omikron – the virus has no idea.