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The vaccine may be only 39% effective against infections by the Delta variant.

Granted, this is just in one study from Israel, for just certain kinds of vaccines. But still, I've spent a great deal of time over the last week thinking about this number. Why is this such a big deal? Because, if this is true, and if that 39% holds constants across a variety of circumstances, then we're in a lot of trouble. This would mean that the Delta variant would be unstoppable, EVEN WITH THE VACCINE.

The "unstoppable" scenario

Now, all that is a big "if". But under that "if", the virus would punch through the vaccine's protection and eventually spread to a vast majority of the population. A lot more people would die. Here's how it would go:

The Delta variant has a R0 of about 7. A vaccine with 39% effectiveness brings it down to about 4 - which is still much higher than the original strain of covid, which hand an R0 of about 3. In other words, you're MORE vulnerable to Delta AFTER being vaccinated, than you were to the original strain before being vaccinated. The resulting R value is big enough that there isn't a whole lot we can do about it - not with simple measures like masking mandates or six-feet social distancing. After all, we tried that for much of 2020, and that was hardly enough to contain the original strain. The only thing that might work is a lockdown, and we're not doing those again. So there's little we could do. Everyone's getting infected.

Fortunately, the vaccine is very effective at preventing serious illness and death. So the consequences for getting infected won't be that bad for most people - but for the elderly and the otherwise vulnerable, this still amounts to a significant risk. Multiplying that by the number of relevant cases in this scenario, we still end up with some hundred thousand additional deaths - again, EVEN IF everyone gets vaccinated.

The "easy" scenario

Now as I said, all that is a big "if" - and that "if" may not hold. There's several reasons to think so. That 39% may be a low outlier - either as a statistical noise in the study itself, or among the vaccines available. Furthermore, there is probably a compounding effect which increases the vaccine's efficacy. That is, even if you get infected through the vaccine, you're less likely to become symptomatic or severely ill, so you'd be less likely to pass it on to others. This would mean that, over a chain of multiple infections, the average effectiveness of the vaccine is much higher than 39%.

I find the above set of scenarios quite likely. Some countries have managed to contain an initial outbreak of the Delta variant, lending further credence to this scenario. In that case, a vaccine by itself may be enough to stop the spread: once you're vaccinated you've done all that could be required of you, and you can go on with your daily life. This seems to be the dominant thinking in our society right now.

The criteria for a decision

What should we do about these scenarios? How should we choose between them, when they offer such different outcomes with such uncertainty?

In crafting my decision, I must take several things into account.

First, I have to be realistic. I am not making a decision for the whole world or for the whole country. I am making it for myself. I am responsible for myself and those close to me, in either physical proximity or their place in my heart. If I had mind-control powers over the population of the country, I assure you that all this would have gone very differently. But I do not have such powers, and it doesn't help to pretend to have them.

My decision must still be applicable to the general public. I will not act in a way that I would not want others to act. If my decision were to become public policy or a universal law, I should still be happy with the outcome, and the public in general must also feel the same.

The decision must still cover over both scenarios, disparate as they may be. I don't want to make a decision that will be catastrophic in one scenario because of my preference for the other scenario. If a catastrophe cannot be eliminated altogether, then its probability and magnitude must be minimized across both scenarios.

In the "easy" scenario, the decision is simply to get vaccinated. But what about the "unstoppable" scenario?

Herd immunity through infection

Currently, our policy is to achieve herd immunity through vaccination. But in the "unstoppable" scenario, I think, we would need to pivot to a different strategy - herd immunity through infection. The idea is to let the virus spread naturally through the population, while protecting the vulnerable. The goal is to get the low-risk group get infected and therefore immunized, while the high risk group remains uninfected, and protected through herd immunity.

This sounds scary - letting the virus run through the population? Indeed, this plan was briefly considered at the very beginning of the pandemic by the UK, but it was abandoned due to its high cost in human lives. So what makes it okay now? What's changed since then?

First, we may not have a choice. If we're really in this scenario, where the vaccine is only 39% effective, nothing else is really possible. Vaccination alone will not work, and masking on top of that will likely prove ineffective. At that point it's a forlorn and ineffectual hope to simply cry out for harsher measures and stricter social distancing. Remember, we have to be realistic, in light of the policies which were hardly successful in the past year. At this point we might as well embrace the inevitable.

Second, again consider that past year, with its 600,000 dead. Losing a million people to this pandemic was unthinkable at its start, but we're already 60% of the way there. A policy that kills another few hundred thousand may not be appealing, but given its inevitability and the price that we've already paid, it may be tolerable.

Lastly, there's the vaccine itself. In this scenario, the vaccine is lousy at stopping the infection, but still great at stopping hospitalization and death. The "herd immunity through infection" then plays to the strengths of the vaccine, by preventing the vast majority of bad outcomes as most people get infected. This is what fundamentally changes the calculus behind this policy. At the beginning, the UK decided against it because the cost in human lives was too high, while the alternative - containment - had a good chance at success. In this scenario, the cost in human lives is reduced by a factor of 10 thanks to the vaccine, while containment has little chance of success.

The plan in this scenario, then, would be to let the virus spread, while protecting the vulnerable from the infection. So, how does that translate into action?

The action plan

The following is what I will do, and what I recommend for others. It takes into account all the considerations I mentioned above, including balancing over both scenarios.

First and foremost, get vaccinated, as I have already been. There is no scenario in which the vaccine doesn't play an absolutely crucial part of the overall plan. This takes care of the "easy" scenario.

I will not wear a mask, or practice much social distancing, around young, healthy, and vaccinated people. The risk posed by the virus to such people are comparable to that of a car accident. And if anyone here does get infected, that's one more contribution to reaching herd immunity, if we happen to be in the "unstoppable" scenario.

I will not intentionally try to get infected. If the vaccine really can't stop the virus, it'll come for us all eventually.

Around the elderly, infirm, or the unvaccinated, I will wear a face mask, practice social distancing, and ask that they do the same. They bear increased risk of bad outcomes if they get infected, and so should be protected from the infection until the rest of us reach herd immunity.

So for me, in practical terms, this works out to "wear a mask when I'm grocery shopping, but not when I'm at the gym".

This, I believe, satisfies all the requirements I mentioned above. It is implementable on an individual or group basis. Any one person, or any group of people, up to and including the whole country, can adopt it. It will benefit any such individual or group, and those close to them. All this will be true in either of the two scenarios I mentioned above. Naturally, I will change course as new information comes in, but for now, I believe this to be a robust plan of action.