Delta, masks, and making sense of what's happening

What should we be doing?

Did you think we were done with the pandemic?

When we were experiencing exponential decay in cases and vaccine uptake was rising, I was optimistic that the worst of the pandemic was over. But then the Delta cases started rising and our case counts among vaccinated people started creeping up:

You may have heard about the new CDC recommendations about mask wearing in public indoor spaces even if you’re vaccinated.

And if you’re anything like I am, you reacted with dismay and frustration. I’m sick of wearing these damn masks and I’m sure you are too.

But the new CDC guidance for the vaccinated was particularly disappointing, if only because many of us thought vaccination was our ticket to freedom, not to ongoing restrictions and mask wearing without an end in sight.

What gives? If the vaccines work against Delta, as the evidence seems to suggest, then why are the recommendations changing? And what should we do?

As always, when it comes to what I do myself and what I recommend for my individual patients, I go back to the data to make sense of what’s happening.

The CDC slides behind their recommendations leaked to the public, so we can review it ourselves. I’ve also been reading papers on breakthrough infections, transmission, and how Delta changes the equation.

Let’s take a look at some of the important things to know.

Post vaccine “breakthrough infections” aren’t usually serious

A “breakthrough infection” is a COVID infection that occurs in someone who is fully vaccinated - fully vaccinated meaning 2 weeks after the last dose of your vaccination regimen.

But not all breakthrough infections are created equal.

It doesn’t just matter if you get sick, but how sick you get and how much you spread the virus.

So when you think about the Delta variant, the first thing that I care about is how sick people get when they’re infected. I think about this in a multi-step process:

  1. Vaccination dramatically lowers your chance of getting infected

  2. Even if you’re infected, your chance of symptoms is incredibly low

  3. Even if you are infected and develop symptoms, your chance of being hospitalized is incredibly low

  4. Even if you are infected, develop symptoms, and become hospitalized, your chance of needing a ventilator or death is incredibly low

From the CDC slides:

So, in summary: the vaccines are good on an individual level and protect you immensely from COVID.

Post vaccine spread is slower than unvaccinated spread

The spread of a pathogen during a pandemic will often matter more than how virulent the pathogen is - that’s part of why a variant that spreads more efficiently is so worrisome.

If you think back to the very beginning of the pandemic, you may remember the concept of “flatten the curve” which was the impetus behind many of the societal restrictions that we were facing.

Our goal wasn’t eliminating COVID, just making sure that hospital capacity wasn’t overrun, so that everyone who needs a ventilator gets a ventilator and we don’t run out of oxygen or medications.

You may have heard something along the lines of “Delta variant infections in vaccinated people may be as transmissible as in unvaccinated.” It’s true, but incredibly misleading.

The CDC slides describe something called the “cycle threshold” or Ct, which is a quantitative measure of how much virus an infected person has. The alarm from the CDC report is that there was no difference in the Ct value between vaccinated and unvaccinated cases. But you need to remember that when you’re vaccinated, you clear the virus much more quickly.

What does that mean in practice? Two things:

  1. People with breakthrough infections can spread disease, BUT

  2. The duration of disease spread in a post-vaccine infection is shorter than an unvaccinated infection.

The outbreak in Provincetown, MA was really concerning for many people who were previously feeling better about the course of the pandemic. And while the media made a big deal of this mini-superspreader event, understanding what actually happened there should make you more confident in the vaccines rather than less confident.

I recommend this Twitter thread from Ashish Jha to better understand what happened there:

Why does the CDC recommend that we mask again?

Masks fall under the umbrella of NPIs (non-pharmacologic interventions) that can be used to protect against COVID. They’re one layer of the Swiss cheese model of slowing a pandemic:

The idea that masks work comes from research documenting the flow of particles in and around masks and extrapolated to suggest that masks prevent the spread of COVID.

The CDC’s modeling suggests that the vaccines are 75-85% effective against symptomatic infection and that masking provides additional personal benefit and protection against spread. From the report: “Given higher transmissibility and current vaccine coverage, universal masking is essential to reduce transmission of the Delta variant.”

While this is certainly a reasonable recommendation - and I recommend that you mask up when you’re required to - it’s not as though masks have been rigorously tested so that we fully understand the risks and benefits.

Mask mandate effectiveness hasn’t been studied, so we don’t know how much they actually work in practice. You can add the lack of rigorous testing of NPIs to our extensive list of public health failures throughout the pandemic.

Plus, there’s the risk of second order impact from adding mask mandates, as Vinay Prasad writes:

“It is bad enough we have learned nothing about when and if mask mandates offer net gains, but this is compounded by the potential for second order effects.

If you start making vaccinated people mask again, will that be a disincentive for the "vaccine curious" to vaccinate? After all, they are already hesitant -- could they take from the guidance the tacit message that the vaccine is not that protective after all? P.S. -- The vaccine is that protective, and it retains amazing efficacy against Delta!

Will reinstating mandates be met by the same level of compliance as before? Will it lead to protests which have rocked other major global cities?

Worst of all is the likely scenario where the places with the political will to reinstitute mandates are probably liberal urban areas where vaccination rates are the highest and SARS-CoV-2 rates the lowest. Places that will be allergic to mask mandates -- southern, rural areas -- might be places where vaccination rates are the lowest and SARS-CoV-2 rates the highest. Ironically, the CDC's guidance might result in two different scenarios: excessive mask use where it won't help and inadequate mask use in places where it might help.”

In conclusion: get vaccinated and don’t be alarmed

There’s quite a discordance when comparing what I’m reading in the news versus my actual level of alarm when looking into the data on Delta and post vaccine spread more carefully.

These vaccines are amazing. They’re scientific miracles that continue to provide excellent protection even against novel variants.

They’re safe, effective, and available. If you haven’t been vaccinated, I can’t strongly enough recommend that you get it.

More vaccinations are the best way forward from both a public health and an individual health perspective. If the spreading risk of Delta means that more people get vaccinated, then something good comes from something bad.

And so the bottom line here is simple: the vaccines are great, you should get them, and you don’t need to be as worried about the Delta variant as the media would suggest that you be.


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