The word “mild” has probably appeared more in the news lately than at any time since the introduction of filtered cigarettes in the 1950s, when Ronald Reagan and Joan Fontaine plugged “Chesterfield Mildness,” Tareyton claimed “Mildness Makes the Difference,” and Lucky Strikes claimed that scientists had proven its cigarettes to be the mildest of them all. This time around, the mildness in question is still respiratory, but the change agent is the Omicron surge (“Omi” to his friends on Twitter), not cigarette filters.
Since Omicron has proven itself to be insanely capable of transmission, the question of its virulence is urgent: if Omicron infections are far milder (less virulent) than previous COVID cases AND don’t result in very many Long COVID cases AND provide a useful degree of immune protection against subsequent infection by itself and other variants, its arrival could even be beneficial, except to the people who will still die from it.
It could, in this best-case scenario, spread immunity more widely around the world at a more tolerable cost in lives, calming subsequent waves of infections. Not surprisingly, our hunger to believe in Omicron’s possible mildness is blooming faster than scientists can support, even though the science is trending in encouraging directions. Here’s a status report.
First, there’s now lots of data from South Africa, Denmark, the UK and elsewhere showing that explosive growth in Omicron COVID cases has not resulted, so far, in proportionally rapid growth in hospitalizations and deaths. Hospitalizations and deaths are rising, but more slowly than they did in the surges caused by previous variants—in South Africa, one dataset shows deaths 70% less than predicted, where predictions were based on South Africa’s recent (and horrible) experience with a Delta surge.
One thing these places have in common is a high proportion of the population is seropositive (meaning vaccinated or previously infected/recovered). Omicron’s biggest trick is to readily infect people who are seropositive from, apparently, all vaccines and previous variants. Since such people are less likely to be hospitalized or die, Omicron is automatically going to throw up gaudy “mildness” statistics. In jargon, its “contextual virulence” is reduced, whether its “intrinsic virulence” has changed or not.
It’s harder to determine Omicron’s intrinsic virulence relative to other variants, but data is trickling in, and it doesn’t totally suck so far. It seems likely now that Omicron is not intrinsically more virulent than Delta, and quite possibly less. It may still be more virulent than its own ancestor, which was a pre-Delta variant. Contrary to a popular meme going around now, there’s no automatic correlation between greater transmissibility and lesser virulence.
It’s true that, at the extremes (eg, Ebola), a pathogen that kills its victims before it can spread from them is disfavored by natural selection, but that condition doesn’t apply to SARS CoV-2 at this point—the selection pressure away from causing death is very slight. Selection pressure may push it that way over the next few years (or not), but if Omicron is milder than Delta it’s good luck, not a law of nature.
It may turn out that the set of mutations which improve its transmissibility also directly reduces its virulence, or perhaps some of the other mutations (it has over 50) reduce virulence; this topic is the subject of urgent research. There’s preliminary lab evidence (as compared to “real life” evidence) that Omicron has given up some of its ability to infect lower respiratory cells compared to Delta, and perhaps even compared to earlier variants. There are plausible hypotheses about why this might be true and bits of data to support them, so there’s hope that the intrinsic virulence of Omicron might be less than Delta or even earlier variants. So far, hope is more the thing with feathers than the thing with strong data, but some of the worst scenarios are becoming less likely, and so hope is fledging out a bit.
Even if Omicron turns out to be both intrinsically and contextually milder, its extreme transmissibility could overwhelm those protections and make it, overall, more dangerous. In simple terms, the transmissibility gives the virus more chances to solve the puzzle of you, and it only needs to succeed once. Sadly, the Omicron surge is certain to stress our healthcare workers to extremes again, which makes this surge more dangerous for everyone. The best strategy for individuals and families is still vaccination, booster shots, minimal time indoors with groups of people, maximum ventilation, and good, well-fitted masks. As before, only more so, since this variant is so insidious. At least the worst-case Omicron scenarios have faded in likelihood, and some of the better-case scenarios are still on the table. Take your comfort where you can get it.
Since we’re on the topic of hope, there’s one other recent development that deserves mention: the progress toward an all-coronavirus vaccine which prepare the immune system to block all SARS CoV-2 variants as well as other coronavirus diseases such as SARS and MERS. The lab at Walter Reed Hospital has developed a candidate vaccine in this category and proven it safe and effective in monkeys. This is a significant breakthrough: it is now ready to move on to human trials. There are still many steps to go, but such a vaccine could possibly end the pandemic, not just temper it.
Meanwhile, the Omicron tsunami is coming ashore in the US now and will rapidly shatter all previous records for new cases. Since the mildness questions are still mostly unanswered, people vary in their inherent vulnerability, and there’s no data at all yet about Omicron’s potential to cause Long COVID, hunker as far down as you can for the next month or so. A surge with an attack slope this steep has a greater chance to also fall away sharply as it quickly burns through the most susceptible targets. Hang on tight, and hope Omicron misses you but burns down Delta.