Covid-19 Information Confusion

The data is not what you think it is

Welcome to Plugging the Gap (my email newsletter about Covid-19 and its economics). In case you don’t know me, I’m an economist and professor at the University of Toronto. I have written lots of books including, most recently, on Covid-19. You can follow me on Twitter (@joshgans) or subscribe to this email newsletter here. (I am also part of the CDL Rapid Screening Consortium. The views expressed here are my own and should not be taken as representing organisations I work for.)


Today I want to highlight a couple of issues that have come up with respect to the information we are receiving on the pandemic. This will cover the data on hospitalisations of children and our expectations of what infections mean after you are vaccinated. These don’t necessarily seem related but that are … in each case, the information you see needs context to be interpreted.

How many children are hospitalised with Covid?

Very few. Here’s the data:

But what are those numbers? Those numbers are the count of people admitted to a hospital and testing positive for Covid-19.

Now if the process for getting this data was:

(1) someone has Covid-19 symptoms then (2) goes to hospital then (3) receives a Covid-19 test then (4) is positive

that would be one thing. But what if the process is:

(1) someone is sick then (2) goes to hospital then (3) receives a Covid-19 test then (4) is positive

The first step is the difference. Pretty much everyone going into a hospital is being tested for Covid which means that some people will be admitted for something else — say, a broken leg, cancer or you name it — but then are testing positive for Covid out of chance and are then being counted in the Covid-19 hospitalisation statistics. This may not matter if there is a surge in hospitalisations in an age group because of Covid. But it will really matter if Covid-19 isn’t a hospitalisation risk for an age group.

A couple of new studies published in Hospital Pediatrics did an audit of hospitalisations for children and found that 40% of those listed as Covid hospitalisations were not there because of Covid at all. This is from a New York Magazine write-up:

In one study, conducted at a children’s hospital in Northern California, among the 117 pediatric SARS-CoV2-positive patients hospitalized between May 10, 2020, and February 10, 2021, the authors concluded that 53 of them (or 45 percent) “were unlikely to be caused by SARS-CoV-2.” The reasons for hospital admission for these “unlikely” patients included surgeries, cancer treatment, a psychiatric episode, urologic issues, and various infections such as cellulitis, among other diagnoses. The study also found that 46 (or 39.3 percent) of patients coded as SARS-CoV2 positive were asymptomatic. In other words, despite patients’ testing positive for the virus as part of the hospital’s universal screening, COVID-19 symptoms were absent, therefore it was not the reason for the hospitalization. Any instance where the link between a positive SARS-CoV2 test and cause of admission was uncertain the authors erred toward giving a “likely” categorization.

The other study found the same sort of thing.

The risks to children seemed small before this information. But we now know that, by understanding the context with which the data we have was generated, it was misleading but a very large amount. This actually matters if you are thinking of vaccinating younger kids.

Are vaccinated people likely to get Covid-19?

Yep. 8 fully vaccinated members of the New York Yankees tested positive for Covid-19 this week. That organisation does routine PCR tests. So those positive people had to be isolated which meant some couldn’t play.

But again context matters. The Yankees are doing routine PCR tests that picks up minute traces of the virus in you. In this case, if they didn’t do the tests, those cases would not have been picked up. The question is: does merely having a Covid-19 infection matter following vaccination? Or does it matter enough to isolate people and disrupt organisations?

The answer currently seems to be ‘no.’ Pretty much everyone is going to get Covid now after they have been vaccinated. A vaccine is not a shield of power around your body where coronaviruses look at you and, say, “nope, can’t go there.” Instead, they go there and don’t get much traction in terms of replicating. The immune system kicks in (which, by the way, can give you symptoms even — you know, like when you get coronaviruses that give you colds). The immune system protects you and it also keeps the viral load down which can protect others. That last part isn’t perfect because it is possible that there is still risk to others who aren’t vaccinated. Children already have a good immune system which is why they are lower risk. The elderly not so much.

The point is that for vaccinated people we need to consider why we are testing and for what purpose. In other words, being infected or not isn’t that useful information. On the other hand, how much of the virus might be in you, is important.

Here is Michael Mina being interviewed by New York Magazine:

It seems like you don’t think these are “breakthrough” infections and also that you’re not surprised to see them.
The Yankees are testing themselves frequently. When that happens, especially if you’re doing PCR tests, you’re going to find exposures and infections.

Even in people who’ve been vaccinated?
Yes. I’ve always said that it is very unlikely that these vaccines will create fully sterilizing immunity. Sterilizing immunity is the kind of immunity where, if you get exposed and the virus lands in your respiratory tract, it will be neutralized (or killed) immediately. It will not have a chance to replicate. On the other hand, you can have very highly protective vaccines that are not fully sterilizing — vaccines that prevent you from illness, especially severe illness, but may still allow the virus to grow.

And a PCR test would catch those kinds of infections?
This is a technology that can catch just ten molecules of virus. But this is a virus that when it is contagious, there are billions of molecules. So we have to be very careful about how we interpret PCR results. Just because the virus can grow a bit — and be detected on a PCR test — does not mean we are stuck in the woods as far as herd immunity goes. A vaccine that doesn’t create sterilizing immunity can still greatly limit virus growth, perhaps enough to massively limit transmission. This is likely the case with the mRNA vaccines at least, given the large reductions in cases among kids in hospitals as a result of the adults getting vaccinated. Clearly transmission declined significantly enough to elicit some level of herd effects on the kids.

But it probably won’t decline to zero.
As I have been saying since last summer, we should expect reinfections following infection or vaccination. This should not come as a surprise to anyone. The real question is do those reinfections matter — or more to the point — do the reinfections have negative consequences?

Do we not have to worry about infections of that size?
In my opinion, if they’re not infections that are causing disease, they should be viewed very differently from a breakthrough case, which is a term that should absolutely be reserved for a case that’s causing disease.

Why?
A breakthrough case is a case where the diseases is literally breaking through the type of protection we expect the vaccine to provide. And the clinical trials of the vaccines and their authorization hinged on whether they prevented disease in the vaccinated individual, not based on their ability to stop spread.

Mina goes on to recommend a change in testing:

How can we distinguish between an infection we don’t have to worry about and one that could cause sickness and be transmitted?
The simple answer is that we can look at viral loads. Now that the vaccines are being rolled out, the story is going to come out in a much more robust fashion. But it’s the same story that I’ve been telling this entire pandemic: Extraordinarily low viral loads should not, right off the bat, be considered infectious. Instead, we’ve taken the opposite approach: If you’re positive on a PCR test, you’re considered infectious, and you should isolate, no questions asked, no nuance of what that PCR result means.

But a lot of people aren’t actually infectious when they’re PCR positive — it’s just a little bit of virus replicating but not enough to necessarily transmit and certainly not enough to warrant a ten-day isolation anymore. You can test positive on a PCR machine for up to four or five weeks after you’ve stopped being infectious, which can be a period as short as just three days. Sussing this out is where antigen tests come in.

These are the rapid tests we’ve discussed before.
They will only really turn positive when you’re truly positive and infectious.

Another way to put it is that, when it comes to public-health testing, the PCR test is full of false positives. To be clear, they are real positives, biologically, meaning the primers are actually binding the correct viral RNA, there is actually SARS-CoV-2 there, but does it always necessarily mean you have to isolate? If you are no longer infectious and the PCR test is telling you you are positive and that is interpreted as needing to isolate, then I would call that a false positive from a public-health perspective.

Mina’s point is that rapid tests are more accurate in determining whether someone is infectious (a risk to others) or not. This is even more true if someone is vaccinated. That is because it is very unlikely they have a high viral load.

In other words treating infection as much more of a spectrum, when throughout the pandemic we’ve treated it much more as a binary matter. 
Right. The way we’ve been using PCR thus far is the equivalent of saying that you either are completely immune to a disease, or you’re completely vulnerable. But we all know that you can get a little bit sick or you can get a lot sick, and that those are two really different things.

That had its own cost throughout the pandemic, of course, but it’s also meant we’ve sort of poorly educated the public about how to navigate the post-pandemic, as this episode with the Yankees shows.
That’s exactly right. Binarizing all of these results, and continuing to put everything in black and white — that has been immensely destructive. One of my core philosophies in public health is we absolutely need to bring the public along. You need to keep them up to speed. You need to keep them informed. If you don’t have the public buy-in for everything you’re doing, you will never defeat a pandemic.

Throughout this pandemic, we’ve generally considered the public to be the problem. But this is public health. The public isn’t the problem – that’s on the virus – instead, the public is the solution. As we are seeing with vaccines, the public is the solution and unless we want to vaccinate people based on some forceful military state requirements (which we do not and I hope never would) then we must see the public as the solution, always.

So we need to bring the public along. You need to keep them up to speed. You need to keep them informed. If you don’t have the public buy-in for everything you’re doing, you will never defeat a pandemic. What we’ve done instead, by assuming that the public was unable to deal with this kind of information and this kind of nuance, we have done immeasurable damage.

This doesn’t mean we shouldn’t test. It means we should test more routinely precisely because we need to monitor the situation. But we should use antigen tests because they are more informative. The reason is: our defaults have changed. We don’t have to worry as much about vaccinated people getting infected. We should expect it and not “go crazy” when they are so.

So there’s little downside to getting infected after you’ve been vaccinated?

Well, I wouldn’t say that. First and foremost, if you can transmit despite not getting sick, then such exposures pose a public health risk to those who are not yet protected, even if they are serving to boost your own immunity. This is particularly important as it pertains to being around the elderly – even those who have been vaccinated. Elderly aren’t good at holding on to their immune memories and so we have to be very careful in our assumptions that vaccinated people are protected. I suspect that, come late fall and winter we will see renewed cases and these will spill into the ederly vulnerable population whose immunity will have waned sufficiently by then… a year since vaccination… to allow them to become ill if reinfected from someone who is exposed, infected but  because of vaccination, not sick and not worrying about if they are exposed.

Also, immunity is rarely 100% and so if you are getting exposed post-vaccination, even if you aren’t elderly, there will still be a chance that you’ll get sick. Though this doesn’t seem to be very common and when people do get sick it doesn’t appear to be particularly severe. How long that kind of protection lasts though… time will tell.

One last thing

In case you are interested in a interview with me: