How much should we panic about Delta?

[liv]

So. The US CDC have suddenly announced that vaccinated people should wear masks, because new evidence (mostly in the form of leaked preprint data and internal discussions, which isn't great) shows that Delta is much worse than the previous variants.

Two pandemic watchers I respect, and who have good track records of being right, have reported this as a complete disaster.
siderea: Update on Vaccination and the Transmission of COVID-19:

Vaccinated people remain as fully contagious as unvaccinated people. At least where Delta is concerned [...] So, no, we're not going to get any sort of reduction in transmission (except of the earlier strains of SARS-CoV-2), and, no, we're not going to get any sort of herd immunity out of our present vaccinations.

Deepti Gurdasani: Delta has changed the course of the pandemic:

While we're really lucky that vaccines still protect well against severe disease with delta, the reduced vaccine effectiveness in preventing infection is problematic from a population immunity perspective.

In contrast, two pandemic watchers I respect, and who have good track records of being right, think the picture isn't quite that bleak:
Zeynep Tufekci writes in the New York Times (paywalled but fairly easy to evade): The C.D.C. Needs to Stop Confusing the Public:

[The claim by the CDC] that [vaccinated people infected with Delta] had “the same capacity” to transmit it as an unvaccinated person certainly was [surprising] including to many experts

(Sorry about the heavily doctored quote, Tufekci has a slightly flowery style and the pullquote has lots of referents from several sentences back. If you follow the link you can see that my insertions are accurate.)

Ed Yong in the Atantlic: A nuanced guide to Delta

Vaccinated people are unlikely to transmit Delta as easily as unvaccinated people … but they can probably still spread it.

A fifth expert, John Skylar, gives us a Deep dive on the CDC leaks and in keeping with his usual approach of cautiously waiting for more evidence before drawing any strong conclusions, says only

The war has changed. Delta is a serious threat. On the other hand, vaccinated people are still extremely well-protected.

While challenging some of the more extremely pessimistic interpretations of the CDC's data and models.

I am ignoring noise from random pro-pandemic or anti-vax dickheads here, so I'm not including any links to claims that it's all fine, we can just rely on vaccines to give us some extremely non-scientific definition of "herd immunity" and the pandemic is "over" now. Nor any to claims that the data proves that vaccines don't work and we should avoid putting scary things into our pure precious bodies.

That said, I don't think there's any data at all that warrants siderea's strong conclusion that vaccinated people are as fully contagious as unvaccinated and we will get no reduction in transmission and no herd immunity. Even the most pessimistic studies say that vaccines reduce infection with Delta variant by at least half, several show better than that. So vaccinated people are at worst half as likely to transmit Delta variant SARS-Cov2 as unvaccinated people, because if they never get infected in the first place they won't transmit the virus to others. I give much more credence to Gurdasani's statement that

those who do get infected [with Delta variant] have virus levels that are similar to unvaccinated & can likely transmit as efficiently.

Whether this means we will or won't "get" herd immunity sort of depends on how rigorously you're defining herd immunity, but to say we're not going to get any sort of herd immunity seems excessive. Other vaccines with considerably lower effectiveness than any of the licensed Covid vaccines give us partial herd immunity against other diseases, from measles to flu, and I'm pretty confident the new vaccines will be similar against Covid.

I think the inferences that siderea makes from an overly pessimistic read of the data are largely still sound, though. It is very hard to question the basic conclusion that Delta is much worse (in a handwavy lay sense of the term "worse") than any previous variants we've had to deal with, and it certainly does change the balance between vaccination and disease, and it certainly does mean we're still in the pandemic, and we need to deal with that psychologically and on a policy level.

I strongly recommend you read Tufekci and Yong, in terms of facts about where we are with the Delta variant and our protective measures. I would certainly like to believe the interpretation that the faster dropoff in viral load in vaccinated people at least partly counterbalances having the same peak of infectiveness, so that in fact vaccinated people are a lot less likely to be infected at all, and if they are infected, somewhat less likely to transmit the virus to others. But on a practical level it doesn't really matter whether I believe that or not. Getting vaccinated as soon as you can in your country is clearly still a good idea. Taking as many reasonable precautions as you can cope with to avoid getting infected and to avoid infecting others, even if you are vaccinated, is clearly still a good idea. I also strongly recommend you read siderea's advice in her excellent series of posts on the pandemic, on how to respond to bad news about variants and to viewing the pandemic as an ongoing, long-haul disaster not just a short-term emergency or a thing of the past.

Comments

[redbird]

I think siderea is more inclined to be pessimistic because she spent significant time researching, and posting about, the 1918-19 flu epidemic, including the ways that the disease was spread by people assuming that "sailors" in this port city"civilians" were separate populations that didn't interact. And then spent winter and early spring of 2020 advising people to say home, and stock up on things like non-perishable food, and being told she was over-reacting. That said, I'm not as worried as she is, but we're looking at the same situation--she lives somewhere within a few miles of me.

Possibly relevant: they have impressively good documentation and contact tracing for the recent Provincetown outbreak, because the gay community is still primed to worry about disease transmission, and because of a citizen scientist who's been blogging about covid since early in the pandemic. People were giving the contact tracers their itineraries, and the names and phone numbers of people they'd interacted with--and in many cases they had already called or emailed those contacts to tell them to get tested.

That's a snapshot of one community, of course, but a high-resolution one.

[liv]

Yeah, on a broad level I'm not at all optimistic that we're going to handle this better than they did in the post-WW1 flu epidemic. Even though we have far better tools at our disposal, not just vaccines but sequencing, reliable molecular testing, far better medical technology (ventilators for goodness' sake didn't exist 100 years ago), far better rapid mass communication... The pandemic has been politicized, and the numbers of people who are explicitly on the side of the disease means that we're going to mess this up even worse than they did with the flu.

So it's not that I'm more optimistic than siderea in general. Recall that I'm in the UK where we never even had a break between reaching high levels of vaccination and Delta taking over the population. There was essentially no time here when we could reasonably have planned for 'Hot Girl Summer' or 'back to normal'. There was almost no time between getting clear data saying that the vaccine prevented transmission of the pre-Delta variants, and ending up with Delta and going back to, we have to assume it probably doesn't fully prevent transmission. I'm only more optimistic on the specific claim that vaccination only protects individuals and doesn't improve the population situation at all.

The Provincetown story is amazing, thanks so much for linking to that. I'm also following Iceland which is a small enough country that they routinely test and contact-trace the entire population, so again, very detailed data.

[oracne]

Thanks for all these links.

[starlady]

My understanding is that not all infected vaxxed people are the same in terms of transmission either--asymptomatic people to my knowledge don't have a very high viral load at all, rather it's just the people who are symptomatic. And from what I've read most symptomatic infections stay in the nose and throat and are cleared within a few days, so even though the viral load is almost as high as an unvaccinated person it's for a much shorter interval of time. And I guess I would question sidera's argument that we're not going to get a reduction in transmission from vaccinations--if everyone were vaccinated, we certainly would, and inasmuch as vaccinated people are getting a bad cold rather than a fatal respiratory disease, albeit with a random chance of long-term post-viral syndrome, we're not in the same position as in March 2020.

I thought this article was a good overview of why Delta is different using some actual epidemiological math, demonstrating that vaccinations have already caused a reduction in transmission and that continuing to vaccinate new people will further reduce it. We will have to keep masking for a while, for sure, particularly here in the States where we're still struggling to vaccinate more than 50% of the population. This isn't entirely unlike the 1918 influenza pandemic, either, which did last about two years. I think it's reasonable to suppose we might also have a few major recurrences after that like the OC 43 pandemic. But I don't think we're doomed, particularly if we adopt booster shots as seems to be the emerging consensus.

[liv]

I think the data about vaccinated people clearing Delta infections quickly is preliminary and equivocal, so I've marked it down as something I'd like to believe rather than something I definitely do believe. Even so, the vaccines' high efficacy against severe disease is still very, very good news.

Thank you for the epidemiological calculations article. It does seem very plausible to me that it's more important to get vaccine into unvaccinated people than to give boosters to the already vaccinated. And I absolutely agree that we need other strategies alongside vaccinations, masking seems like a no-brainer since it's such a low-cost response. We have very strong evidence now that improving ventilation helps a lot. Whether there's the political will to do it is another thing; if we continue to rely on vax only this is going to drag out for a long time, especially if we hoard vaccines in the rich countries and don't consider global distribution.

[sara]

Yep. Thanks.

[steorra]

Your assessment of the situation sounds fairly similar to mine.