It seems that we have a vaccine.
There’s finally a light at the end of the tunnel of this pandemic. Don’t get me wrong - the next few months have the potential to be really bad - but the news of a Pfizer vaccine demonstrating 90% efficacy is simply huge news.
You may be wondering why I’m so optimistic about this when we are just getting science by press release instead of a published, peer reviewed analysis.
Well, when the people conducting the trial release a full protocol of their study and then top-line results, that’s a lot of information (if you’re willing to read it)! Trial design - which is described by the protocol - gives us a window into how applicable the trial is. So we’re in a good spot here.
Let’s take a look at what you need to know.
What does 90% efficacy mean?
Vaccine efficacy (VE) is a measure of how well a vaccine works when vaccination goes perfectly according to plan.
VE is calculated by looking at the risk of infection of in vaccinated people compared to risk in unvaccinated people.
Now, with COVID, we care about a handful of different individual outcomes. We care about preventing disease, reducing the severity of disease, and preventing death and disability.
In this trial, efficacy of a vaccine was measured by reduction in symptomatic infection. So that 90% reduction we’re looking at is people with symptomatic infection.
We don’t know about the degree of protection from asymptomatic infection (i.e. sterilizing immunity).
But we do know that if it reduces symptomatic infection, it should reduce deaths, hospitalizations, and intubations as well.
What is the vaccine protocol?
This vaccine requires 2 shots that are spaced 21 days apart.
The most challenging part of the logistics of delivering this vaccine have to do with how it’s stored. The vaccine needs to be kept at approximately -70 degrees C. This temperature is colder than freezers, it basically means that the vaccine is kept on dry ice (which is -78.5 degrees C).
The 90% efficacy assumes that the vaccine is kept at the appropriate temperatures and delivered with both shots 21 days apart.
It’s unclear what disruption of that precise protocol means for effectiveness.
What is the biggest remaining question about vaccine efficacy?
The biggest question that remains in this realm: how does the vaccine reduce ability to spread the virus?
We don’t know if reducing symptomatic infections means that people have asymptomatic infections after being vaccinated. For any one individual, this doesn’t matter all that much - what you as an individual care about is how well you are protected.
But in a pandemic, we care about how the vaccine affects viral spread.
If this vaccine provides sterilizing immunity - i.e. you can’t get infected after being vaccinated - that means a lot more about spread than if the vaccine just makes infections asymptomatic.
With COVID, we care almost as much about whether the vaccine prevents someone from becoming infectious as we do about whether it prevents someone from becoming infected.
The public health benefit of the indirect protection that a vaccine can provide is just so important. There’s an enormous public health difference if vaccinated folks can still spread the virus but don’t get symptoms from infection.
The reason that this is even an issue has to do with when people actually receive the vaccine.
If we knew that everyone could be vaccinated at the same time, then we basically give the vaccine and 3 weeks later the pandemic would gradually come to an end.
But if we’re doing rolling administration as vaccine production and distribution gets ramped up, a lot of folks are vulnerable for a long period of time, probably on the order of a few months to a year.
What other questions should I have about efficacy?
As you might imagine, the initial press release data doesn’t answer all the questions we might have. A few that come to mind for me:
Were all age groups protected equally?
The protocol for this trial enrolled patients between ages of 18 and 55 and then another group between 65-85. We don’t know whether both age groups received equal protection. Because of the asymmetric risk of death based on age (older people at much higher risk), an attenuated vaccine response in the elderly (which is certainly possible) could be a big deal.
How long does immunity last?
Again, this matters because of the logistics of deploying a vaccine to hundreds of millions of people domestically and billions worldwide. Since vaccination is going to happen over a period of months to years, transient immunity could be an issue. And we just don’t have the data to draw firm conclusions here.
What’s left to worry about?
Well, I have 4 major questions about the vaccine before I’m ready to say the pandemic will definitely end:
Is it safe?
Is it safe?
Is it safe?
Will people take it?
When you’re distributing a treatment to millions, even very rare side effects can be important. The transverse myelitis observed in the AstraZeneca vaccine is a good example.
We also have to worry about public trust in the vaccination process and whether people will take a vaccine, which is probably a topic of conversation for another newsletter as this one is getting long.
And then there’s the ethical matter of how this impacts trials moving forward.
What if this isn’t the most effective vaccine and it’s just the first?
With any emergency use authorization for a vaccine (or full approval, for that matter) we lose the ability to give people a placebo in a clinical trail. Once a vaccine is available, it is unethical not to offer it to any control subjects in another vaccine trial. So it becomes impossible to test another vaccine for comparative effectiveness or even to evaluate long term efficacy of the Pfizer vaccine compared to placebo.
These are certainly important issues to address. But that’s for another day.
So, here’s my summary of the Pfizer vaccine news:
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