🧵/Lots of great minds are debating the pros/cons of altering #COVID19 vaccine dosing to a single dose.

Lost in the debate: potential for great harm should the public perceive the shift as anything other than a data-driven decision.

And we lack data to support 1-dose regimen. https://twitter.com/ct_bergstrom/status/1345088693074186244
Simply put: there is insufficient data to *support* the decision to shift to a 1-dose vaccination regimen at this time.

Period. Full stop.
The safety and efficacy data used to justify an *Emergency Use Authorization* for the mRNA vaccines does not argue *against* a 1-dose regimen.

That is *NOT* the same thing as providing data to *support* a 1-dose regimen.

What the UK gov’t is doing is an experiment. https://twitter.com/dereklowe/status/1344644939666358273
As with any experiment of this kind (i.e. a clinical trial), there are 4 possible outcomes:
1️⃣ 1-dose is PROTECTIVE, and HARMLESS
2️⃣ 1-dose is NOT PROTECTIVE, and HARMLESS
3️⃣ 1-dose is NOT PROTECTIVE, and HARMFUL
4️⃣ 1-dose is PROTECTIVE, and HARMFUL

Let’s break them down.
Before I go further, I should mention that my knowledge of immunology, virology, and vaccines goes far beyond rote medical school curriculum:

I spent several years in the lab focused on these areas— including time as a Guest Researcher at the NIH’s cancer vaccine initiative.
That is not to say I am an expert, but that is to say that I can recognize an expert when I see one. For true expertise, please follow @VirusesImmunity and @angie_rasmussen.

To that point, Prof. Iwasaki wrote a thread today that is being taken out of context. https://twitter.com/virusesimmunity/status/1345086669607890945
I welcome @VirusesImmunity to correct me: I did not read her thread as an opinion in favor of a 1-dose regimen— it is an evidence-based argument in favor of a *delayed* 2nd dose.

She cites data from the 2-dose trial to make the point that we can delay for at least a month… https://twitter.com/VirusesImmunity/status/1345086686586400774
It seems like most folks stopped reading her thread after that tweet, but she makes her point abundantly clear in the following two panels:

🔸We lack data to justify a 1-dose regimen

🔸We have sufficient data to support *delaying* the 2nd dose
Here’s the key thing that is getting drowned out by the noise— Dr. Iwasaki highlights open questions that need to be answered in order to safely shift to “delayed 2-dose regimen"

*That* is true expertise — that’s why, when @VirusesImmunity or @angie_rasmussen speak, I listen. https://twitter.com/virusesimmunity/status/1345086709621534722
With all of this in mind, let’s close the loop by circling back to the possible outcomes:

1️⃣ 1-dose is PROTECTIVE, and HARMLESS

This one is obvious, it’s the *best case* scenario. The reason we’re debating at all is because we have no idea if this is the *most likely* scenario.
2️⃣ 1-dose is NOT PROTECTIVE, and HARMLESS
This would occur if
✅ the virus mutates so quickly that a new strain becomes dominant *and*
❌ our current vaccines DO NOT protect for the new strain

The reason we’re debating at all is b/c the UK strain shows this scenario is possible.
3️⃣ 1-dose is NOT PROTECTIVE, and HARMFUL
*Given what we know at this point* this can occur in a few ways:

✅ the virus mutates so quickly that a new strain becomes dominant
*and*
❓the vaccine only yields a suboptimal immune response that actually worsens #COVID19 severity https://twitter.com/natrevimmunol/status/1252648686166913026
3️⃣ 1-dose is NOT PROTECTIVE, and HARMFUL (cont.)

*Vaccinations* save lives, not vaccines, so if:
✅ the public mistrusts the safety and efficacy of the 2-dose vaccine, refuses to get vaccinated
*and*
❓shifting to 1-dose further undermines efforts & we don’t reach herd immunity
3️⃣ 1-dose is NOT PROTECTIVE, and HARMFUL (cont.)

If:
❓the vaccine is only effective for a <2 months
*and*
❓people do not return in time for a booster *OR* we don’t solve the supply-side problems in time

We would end up w/ people who *think* they’re immune but aren’t. https://twitter.com/virusesimmunity/status/1345086709621534722
4️⃣ 1-dose is PROTECTIVE, and HARMFUL

We have enough data to rule this one out. For all the vaccines on the market, including the #COVID19 vaccines:

the benefits of vaccination >>> the risks
Taken together:

🔸UK variant reminds us that we’re working against the clock
🔸Data shows that 2-doses of #COVID19 vaccine = safe and effective
🔸Data shows 1 dose is effective for 1+ mo but ? as to how long
🔸Data suggests that 1 dose could ultimately harm our response effort
🔸If push comes to shove, Prof. Iwasaki and *vaccine, virology, and immunology* experts like @angie_rasmussen, @PeterHotez are ideally suited to offer guidance on how to proceed.

🔸Prof. Iwasaki suggests that we may want to consider *delaying* the 2nd dose, and offers strategies
I hope this thread is helpful to those looking to make sense of the debate on Twitter and elsewhere.

This sort of debate happens *ALL THE TIME* but usually takes place at scientific conferences and in scientific journals.

This is normal: it’s how we keep vaccines 💯

/😷
Addendum: The UK variant arose from a mutation, which made it more infectious. Our #COVID19 vaccines ARE effective against the UK variant.

The concern is that every time a virus replicates is a new opportunity for it to develop a mutation that *could* render a vaccine useless.
👀 Adding @PeterHotez’s response to an NYT article speaking directly to the question of mixing and matching vaccines — spoiler: he asks to see the data. https://twitter.com/PeterHotez/status/1345155530701090816
👀 Adding @angie_rasmussen’s response to a question about the UK’s decision to alter #COVID19 vaccine schedules — spoiler: she asks to see the data. https://twitter.com/angie_rasmussen/status/1344331033227902976
👀 Adding the response from @VirusesImmunity to my comments about her superb thread https://twitter.com/virusesimmunity/status/1345137992877412354
You can follow @DataDrivenMD.
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