There are reports this morning about early signs that Omicron COVID produces milder disease than feared or perhaps milder disease than Delta and other variants. There does appear to be growing evidence of this, or more evidence that Omicron doesn’t produce more severe disease (which is a great thing). But I wanted to flag some caveats and context that I’ve picked up over the weekend.
The first point, which you’ve likely heard, is that our data just isn’t clear or robust enough to know about disease severity. We’re still dealing with spotty and limited data. Critically, patients often take two or three weeks to deteriorate with COVID. And we are only ten days or so into Omicron really starting to spread widely even in South Africa and roughly six weeks since the first evidence of its existence. There are other more specific issues. For instance, the early part of the wave in South Africa was disproportionately young people who always tend to fare better than older people.
One report out over the weekend noted that a high proportion of the hospitalizations in South Africa are secondary diagnoses. So someone enters the hospital to have some non-COVID related surgery and they test positive for COVID. In cases like this these patients were probably not showing signs of severe disease or perhaps any symptoms at all. Other signs like limited ICU usage and oxygen supplementation tend to support that interpretation. If that holds up it suggests that the hospitalizations may be less a proxy for disease severity than we normally think.
In any case, the early signs are definitely encouraging. But we’re too early in the process to have collected sufficient data or been far along enough in the process of disease progression to know fully what we’re dealing with.
Second point. Even if these reports of relatively mild disease are borne out it doesn’t mean Omicron itself produces less severe illness. This part is important to understand and to me at least very interesting in the way it illustrates all the different overlapping factors involved. We noted in an earlier post that a huge proportion of the population in South Africa has already had COVID. A relatively small proportion has been vaccinated. Omicron’s big advantage and why it’s taking off in the country appears to be that it is substantially more able to reinfect people who’ve already had the disease. But just because Omicron can get around that immunity doesn’t mean these people have no immunity at all. So what we may be seeing is that Omicron can reinfect a lot of people that Delta could not. But these people still have some residual immunity. So it doesn’t pack the same punch as Delta or other variants did with people who had no immunity at all.
Third and final point. One thing I’ve picked up through my unwilling redirection into infectious disease reporting over the last two years is that epidemiologists are often more focused on transmissibility than lethality. The reason is simple math: a super lethal disease that infects 100 people will kill fewer people than a less lethal disease that infects 100,000. On an individual level lethality is the key; on a population level transmissibility can be a bigger deal. Even if Omicron is more mild than other COVID infections it seems to spread really, really easily. That might be because it’s inherently more contagious or simply that it spreads among previously infected or vaccinated people and can access more of the population. Whichever it is, even a comparatively mild form of COVID could still swamp hospitals and generate a wave of new disease and death just because it impacts so many people so quickly.
There is some encouraging news. But it’s still tentative. And at population scale speed and scope of spread can be as big a deal as severity.