Why You Should Still Wear a Mask—Even After Getting Vaccinated

 
 
A few Covid-centric items to share today that I trust many will find useful. The first is a top-notch summary by Stat of the current state of knowledge about the coronavirus a year into the pandemic. Given the unprecedented global effort to understand this virus, I expect it’ll be outdated in six month’s time as science marches on, but it serves well enough for now.
 

“The single advantage that’s propelled SARS-2 on its around-the-world quest: People can pass it to others before they start feeling sick or even if they never show symptoms. Together, this accounts for more than 50% of new cases, according to the Centers for Disease Control and Prevention.

This is not the case with the two other coronaviruses, MERS and the original SARS, that in recent decades have spilled from animals into people and raised global alarms. Those infections are much deadlier than the one caused by SARS-2 — MERS in particular — but people are only contagious once they show symptoms. It’s much easier to stop a virus when you have a clear sign of who is infected.

Covid-19 is not just heterogeneous in presentation, but in severity. One in five people who get it never feel sick at all, while another one in five will get severely or critically ill. Experts say the fact that the vast majority of people will recover just fine has made it harder to get everyone to take it seriously — and in turn to take precautions to protect themselves, their communities, and health system capacities. Experts wonder if people might act differently if SARS-2 had a mortality rate like SARS of nearly 10%, as opposed to 1% or less.

“People are like, my cousin got it and he was fine,” said virologist Juliet Morrison of the University of California, Riverside. “Well, you might have a genetic propensity to develop more serious disease, or you might have an underlying risk factor you don’t know about. Seeing how it’s presented in one individual or even the majority of the population does not mean you’ll have the same disease presentation.”

 
It’s those one in five silent spreaders which brings us to the second item: a write-up in The New York Times on why continuing to wear a mask after getting a vaccine is a good idea. The main reason for this is because coronavirus transmission may still occur by a vaccinated person. This possibility arises from the fact that infection risk — and, by extension, transmission — isn’t something the clinical trials by Pfizer, Moderna, and other vaccine makers are designed to suss out. At least, it isn’t the primary goal behind such trials.

Clinical trials are designed to test the safety and efficacy of a particular treatment. And ‘efficacy‘ in the case of a vaccine typically means ‘ability to prevent illness’ (i.e. prevents an infection from establishing disease in the body). It does not necessarily mean that recipients can’t still be infected and spread the virus without developing symptoms. After all, our bodies are utterly teeming with viruses, most of which are benign, and we’re ‘infected’ by viruses all the time in the sense that they find their way into our cells and tissues. But the vast majority of these situations don’t result in our getting sick because the infection is subdued by our immune system before the pathogen’s replication process gets off the ground.

Like its predecessor, SARS-CoV-1, SARS-2 prefers to take up residence in the nose and throat, where it can pass to new hosts by hitching a ride on droplets ejected by coughs and sneezes. Ideally, a vaccine would produce antibodies that circulate to every area of the body in which the virus resides, and stop it from multiplying. But this often isn’t the case in practice; different types of vaccines with different methods of delivery tend to specialize at shutting down infection in certain parts of the body and can be somewhat less effective in other sectors. It’s why nasal vaccines and oral vaccines, for example, are considered the more optimal remedy for respiratory viruses like SARS-1 and -2.

In contrast, the first generation of vaccines from Moderna and Pfizer are, as with most vaccines throughout history, deep, intramuscular injections. The clinical trial data lend strong confidence they protect against illness, but how effective they are at muzzling the virus in the airways is unclear. It may be that these initial recipes are better suited for tamping down viral activity throughout the lungs and stomach, but prove moderately less effective at dispatching antibodies to the nose and throat area — the locus of transmission. If that turns out to be the case, then the virus could still take refuge in a vaccinated person’s nasal region or upper respiratory tract, ready and able to migrate to new hosts, despite not doing any material damage to its current host.

As The Times notes:
 

“The coronavirus vaccines have proved to be powerful shields against severe illness, but that is no guarantee of their efficacy in the nose. The lungs — the site of severe symptoms — are much more accessible to the circulating antibodies than the nose or throat, making them easier to safeguard.

“Preventing severe disease is easiest, preventing mild disease is harder, and preventing all infections is the hardest,” said Deepta Bhattacharya, an immunologist at the University of Arizona. “If it’s 95 percent effective at preventing symptomatic disease, it’s going to be something less than that in preventing all infections, for sure.”

 
The scientists contacted for the story do instill a bit of hope, however, by expressing a middle-ground possibility in which the first round of vaccines don’t arrest the virus entirely but do reduce the viral load in the mucosal tissues (i.e., those lining the nose, mouth, lungs, and digestive tract). Reducing viral load reduces risk of transmission.
 

“Still, he and other experts said they were optimistic that the vaccines would suppress the virus enough even in the nose and throat to prevent immunized people from spreading it to others.

“My feeling is that once you develop some form of immunity with the vaccine, your ability to get infected will also go down,” said Akiko Iwasaki, an immunologist at Yale University. “Even if you’re infected, the level of virus that you replicate in your nose should be reduced.”

 
In short, a vaccine may not always block an infection entirely, but it can prevent you from getting sick from it. What this ultimately means is that people who receive an approved vaccine will be protected against Covid, but could still contract/be infected by the virus and transmit it to unvaccinated persons. And if so, they would still represent a risk to others, thus necessitating the continued use of masks. In effect, vaccinated people would need to think of themselves going forward as asymptomatic carriers until we know more. 

From a public health standpoint, vaccines that don’t stop transmission are less useful than those that do, but the fact is that we still don’t know enough about all the ways SARS-2 spreads or how the first batch of vaccines affect risk of infection and transmission. If it turns out that upper-arm injections ferry sufficient antibody counts to the nose and mouth, then those risks will be low. Alternatively, we may need to wait for mucosal vaccines to arrive that can generate the particularized immune response that blocks both illness and transmission. Or we may end up needing a combination of various delivery types to shore up comparable levels of immunity in the blood and mucosa alike.

These answers will come in time. Until then, wearing a mask and continuing to observe public safety guidelines even post-vaccination is the best way to protect others and end this pandemic as soon as possible.

Scientists also cannot yet say how long immunity (either natural or vaccine-induced) lasts, or SARS-2’s capacity to mutate around our medical arsenal. Based on these two facts alone, mask use is recommended well into the future.

Finally, for those wanting a deeper dive into the science behind this pandemic, this MIT lecture series a friend recently brought to my attention is super informative, albeit impossibly dense in spots (especially lectures 8 and 9, so caveat lector). Dr. Fauci is featured in lecture 4 and is a highlight.
 

 

Further reading and resources:

Image credit: MIKE REDDY FOR STAT

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