I was vaccine hesitant, too
Today’s update: If I push on the spot where I got my shot it’s a little sore. Otherwise, I’ve been in excellent health. I continue to hear reports of low-grade fevers, fatigue, and headaches from others, so do be aware your experience may not be quite as uneventful as mine. It all depends on how enthusiastically your immune system gets involved, and how sensitive you are to that activation.
I have a confession to make: As delighted as I am to have received my shots (and my delight and enthusiasm are not feigned), I spent the greater part of 2020 skeptical about the creation of, development timeframe, and efficacy of any theoretical coronavirus vaccine. I spent several months in the late summer and early autumn anxiously fretting about political pressure and the timeline of a vaccine release. I made up my mind that I was going to wait – 3 to 6 months, approximately – after the large-scale release of any purported vaccine before I got my shot.
I worried about timing. I worried about who I could trust. I worried about what would happen if this shot didn’t actually work well enough to stop the pandemic (at one point, we were hoping that the vaccine would be 50% effective).
So what changed?
In September, a number of major vaccine manufacturers released their trial protocols. Part of being a responsible scientist is designing your experiments in advance, and releasing the trial protocols meant basically that the manufacturers told us what they were looking for, how they were measuring it, and what the criteria were for announcing success before the formal end of the trial.
Understanding what we were testing gave me more confidence than any ongoing news scrutiny — and knowing the numbers that would indicate a tentative success (something that many trials, not just these, have baked into their protocols) – publicly – in advance – restored additional confidence.
And so when the data was released, and the early results were tallied, my questions were no longer about fundamental issues of trust (although one should always continue to ask questions). They were about points of science – in a field where my training gave me enough knowledge to know what to ask. And that’s how I found myself getting my shot in December – and excited to do so – but still wearing my mask, even now.
One question tonight.
It was going to be two – but I write really long posts. So tomorrow: mRNA and vaccination while pregnant or breastfeeding.
Why are we talking about vaccinated people spreading coronavirus? Wasn’t that the point?
Short answer: About one in 20 people who are vaccinated are still going to get symptomatic COVID-19 (although it’s likely to be milder), and we don’t know how well the vaccine protects against infection that doesn’t cause symptoms.
Long answer: Ready for some math?
Remember when I said that the vaccine manufacturers told us what they were looking for? That’s a really important point in understanding what’s going on here. You see, when the vaccine trials were designed, they were designed to test for efficacy against symptomatic infection. Pfizer and Moderna both tested any trial participants who showed symptoms as part of their protocols, but they did not perform routine surveillance testing (testing everyone in the study, symptoms or not, at regular intervals) as part of their protocols.
There’s a lot of math that happens when you design an experiment. Most of it revolves around eliminating the possibility that any results you have are actually due to random chance. I’m not going to delve deeply into statistics here, because honestly very few people find it super interesting (I do!) — but here’s an example of why it’s important to have a statistician involved when you plan your experiment.
Let’s say I’m going to do a classic coin flip experiment. In order to decide whether the coin I have in my pocket is actually fair, I will flip it five times. My mind tells me that if I flip this coin and get five heads in a row, then the coin is obviously not fair, right? Probability tells me that about 3% of the time I’m going to get 5 heads in a row on 5 flips with a perfectly fair coin. This number – the probability that random chance has accounted for my results – is known as p.
And maybe for a coin flip, 3% (that’s a p of 0.03) is an acceptable chance to take. When people’s lives are at stake, researchers like their numbers to be a little more definite, so they involve a statistician to help design the test. In the coin flip above, if I expand my number of flips to 10, there is a 0.09% chance (for a p of 0.0009) that all 10 will be heads by random chance. That’s a much smaller number – and more on the scale of what we’re looking for.
Pfizer and Moderna both released their interim trial data for symptomatic coronavirus infections (the thing the trial was designed to test) – and that data showed 94-95% effectiveness with a p <0.0001. That means that with regard to symptomatic infections, the numbers we are seeing are less than 0.01% likely to be due to random chance.
However.
Neither trial was designed (built specifically to eliminate outside factors) or powered (with the statistician involved up front) to look for asymptomatic infections. That means that any information coming out of those trials (and there is some) about asymptomatic infections is being done as a retrospective or “look back” analysis. There may be enough data to give us an answer (Moderna has submitted some numbers coming from the tests they administered at the time of second vaccination) but it’s never going to be quite as solid as the conclusions that the trial was actually designed to draw.
That means – ultimately – we don’t know how well this vaccine protects against asymptomatic infections. And because up to 40% of infections in unvaccinated people are asymptomatic, that’s a pretty large “don’t know”. If you add that to the 5% of people (1 in 20) who are vaccinated who may still get infected, that’s enough wiggle room for a lot of viruses to slip through.
I’ve been playing role-playing games since high school (if you hadn’t figured out by now what a huge nerd I am). 1 in 20 happens a lot more often than your brain tells you it should, even with the very best dice.
We still have a lot to learn. In order to save as many lives as possible while scientists take the time they need to learn it, I’m going to keep wearing my mask and keeping my distance.
Just in case.
Because every single one of you is that important to me.
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