Sunday, December 13, 2020

How to Waste Vaccine

The CDC estimates that, as of the end of September, there had been 53 million Covid infections in the U.S., 7.7 times the number of reported cases. The current figure is 16.2 million cases, so if the ratio holds, total number of infections is about 125 million. That is probably too high, since the ratio of infections to cases goes down as the amount of testing goes up, so I will guess a current figure of 100 million.

The U.S. has contracted for enough vaccine from the two sources that have been or almost certainly will be approved to vaccinate another 100 million over the next few months. Combine those numbers and we should have 200 million people who either have had the disease and so are very nearly immune or have been vaccinated and so are very nearly immune, getting us at least close to the level required for herd immunity. Add in the number who will have gotten the infection by then and we should probably be over that level, which means the number of infections should start falling.

There is one problem with this optimistic story. As best I can tell from online discussions, the current plan for allocating the vaccine does not include any attempt to avoid giving it to people who have already had the disease, not even to those who have been diagnosed with it. If so, about a third of the first hundred million doses will be wasted on people who don't need them.

One possible argument for doing it that way is that having Covid does not create perfect immunity, there having been a few cases reported of someone who got the disease, recovered, and was later reinfected. But the vaccine does not create perfect immunity either — reported effectiveness for the first two is about 95%. If as many as five percent of those who had had the disease and recovered were still vulnerable to it, we should have had a lot more than a few cases of reinfections.

To make that argument more precise, consider that, as of the end of September, there had been about seven million reported cases. If infection gave only 95% immunity, about 350,000 of them should have still been vulnerable, a little more than one thousandth of the population. Since the end of September there have been another nine million cases, so more than nine thousand of them should have been known reinfections, individuals who were diagnosed with the disease, recovered, and were then diagnosed again. That did not happen. It follows that, while infection may not give complete immunity, it gives considerably better immunity than the vaccines.

Another possible argument is that tests for whether someone has already had the disease have a significant false positive rate. Checking online, it looks as though the false positive rate for most such tests is below ten percent (specificity>.9). At ten percent, that means that if you skip the people who test positive you are vaccinating an additional ten people for every false positive you are not vaccinating, which sounds like a substantial positive. If we had enough vaccine for everybody it might be better for everyone to get vaccinated, but we don't.

If my analysis is correct, current policy is lethally stupid. 

People who know more about this than I do are invited to correct either my interpretation of what is currently being done or my argument for what ought to be.


Max said...

Some other possible reasons why this is the case:

1. It's too logistically tricky to require everyone to get the antibody test and then prove their results before getting the vaccine (aka. open to fraud or incompetence).

2. It's bad from a PR perspective: feels like you're punishing people for already having had the disease - and nobody wants to be accused of being mean to grandmas and "front line workers".

3. People who haven't caught the disease yet may be particularly good at not catching the disease (very good at social distancing, etc). Thus, it's not that important to really immunize these people first anyway. Better to be cautious and get people that could relapse. If they caught it once, they're the kind of people likely to expose themselves to it again, and thus maybe vaccine is more useful for them (variant of the antibodies-don't-confer-resistance argument).

Anonymous said...

Curious if you have any opinions on vaccine safety? Below is a quote from a Nature article worrying about auto-immune effects of mRNA vaccines and there are concerns about selection criteria of the vaccine trial and polyethylene glycol interactions.

> A possible concern could be that some mRNA-based vaccine platforms (54,166) induce potent type I interferon responses, which have been associated not only with inflammation but also potentially with autoimmunity (167,168). Thus, identification of individuals at an increased risk of autoimmune reactions before mRNA vaccination may allow reasonable precautions to be taken. Another potential safety issue could derive from the presence of extracellular RNA during mRNA vaccination. Extracellular naked RNA has been shown to increase the permeability of tightly packed endothelial cells and may thus contribute to oedema (169). Another study showed that extracellular RNA promoted blood coagulation and pathological thrombus formation (170). Safety will therefore need continued evaluation as different mRNA modalities and delivery systems are utilized for the first time in humans and are tested in larger patient populations.

Dan O'H said...

Given the state of politics, the correct tactic is presumably to complain about this on the grounds of caution. Has the vaccine been sufficiently tested on people who have already recovered from covid? Can we guarantee its safety and efficacy?

Depends on one's willingness to make bogus arguments for the greater good, of course

Anonymous said...

I think it's purely political. If they came out and said "there's no reason for people who have already had covid to get vaccinated, at least in the near term", then they have to give up some of the fear-mongering they did about naturally-acquired herd immunity, part of which included fretting over the possibility of the disease only conferring short-term immunity.

Rebecca J said...

I have many different thoughts about this. First, this study shows that there is almost no reinfection from CoVid19, and even where some people get sick again, they are not infectious. Secondly, my husband and I have had the antibody test because we thought we'd had the infection, but since it was months later, we still don't know if we are immune, because antibodies do not hang around that long generally. The definitive test would be on the t-cells, but I don't know where to get that test done, even though I'd really like to know. And then, the methodology of the research to prove 95% efficacy does not convince me of what they really want the public to believe of this vaccine. The study only lasted a month or two. They have no evidence that the immunity conferred by the vaccine lasts, or that it keeps people noncontagious who encounter the virus later on, even though it might keep them from becoming sick. Those questions were not asked or answered.

David Manheim said...

"to vaccinate another 100 million over the next few months"

No, this is wrong - it won't be available and deployed that quickly. (And I will put up money that the number of vaccinated people in the US is under 100m by June 1, if you'd like to bet.)

Ernie said...

Your estimate of the number of people infected is to high. A simple way to get the estimate is to multiply the total number of deaths by the inverse of the IFR (infection fatality ratio). That ratio is somewhere between 0.5% and 1.0%. Last CDC estimate I saw was 0.65%. Using that ratio, the number of already infected is between 30 and 60 million. Roughly half of your estimate.

Mark P said...

Dr. Friedman - You seem to have derived the same conclusion as the authors of the Great Barrington Declaration, two of whom make your point today in the WSJ:

Plus: given the infection fatality rate has a massive gradient, and non-pharmaceutical interventions have their own mortality cost, herd immunity entirely through vaccine is a policy mistake. Mortality is minimized by vaccinating the most vulnerable, skipping those who have been infected already, and letting everyone else go about their business - they can get the vaccine when it is available.

There is already enough vaccine in the US supply chain to achieve that end.

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