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Breaking down the CDC guidance for vaccinated individuals with a public health expert

Verily Head of Clinical Policy and former FDA Commissioner, Dr. Rob Califf, sat down with us to break down recent CDC guidance for vaccinated individuals. Learn more about the science behind the shift in guidelines.

Fully vaccinated people no longer need to wear a mask indoors or outdoors. This has been controversial, with some feeling it's early to make that call. What have we learned about how the virus is transmitted that makes the CDC confident about this recommendation?

One of the most difficult things about public policy is that you need to make a strict yes-or-no, binary recommendation. Scientific evidence is not binary, it grows over time and speaks to probabilities and likelihood of risk. We now have many studies that show people who have received vaccines approved in the U.S. are at very low risk of becoming infected. If they do become infected, they are at very low risk of serious illness. Some vaccines approved globally are less effective than the ones available in the U.S.

From the original vaccine clinical trials, it was clear that the vaccines were very effective against serious illness or death, and now we know there's a low risk of getting infected at all. If you're  vaccinated and in an environment with unvaccinated people or in a big crowd, or riding public transit — the guidance is still to wear a mask to protect the unvaccinated. I would do that as a courtesy to others.

Some states opted to leave mask mandates in place a while longer. What goes into the calculus of a locality or region when deciding its masking guidance?

The CDC actually doesn't have authority over states or local public health agencies. We're seeing that different localities have different risk tolerance. In California, for example, health authorities kept the mask mandate in place until mid-June, while many states with lower vaccination rates have decided to remove mask mandates and reopen.

One concern is people who don't want to get vaccinated generally don't want to mask. What risk do the unvaccinated pose to the vaccinated?

People who received an approved vaccine in the U.S., almost no matter what, have low risk of getting infected. Unvaccinated people with a high viral load pose some risk to the vaccinated, but not much. Currently, we're thinking that being in an enclosed space and the viral load a person has are the biggest factors that go into being a risk to others.

Viral load refers to the amount of virus in the upper respiratory tract. The more virus you have in your system, the more of it you expel when you sneeze or speak. The vaccines create an immune response to suppress the virus, so even if you do happen to get it, you have a lower level of viral load. So we're seeing asymptomatic infections or scenarios where you don't get that sick.

Where does this leave parents of unvaccinated children or the immunocompromised? Are they at greater risk if adults stop wearing masks?

Children age 12 and older can now get vaccinated, so we strongly recommend parents of older children help them get vaccinated. For kids under age 12, it's a dilemma. The recommendation for younger children is to continue to wear masks and social distance, but this can be a challenge with summer activities. I expect we'll learn more over the summer about how to best manage risk for younger children, with more safety data.

Similarly, for the immunocompromised, the recommendation is to continue to mask and stay distanced. The best thing people can do to protect the immunocompromised is to get vaccinated.

As you mentioned previously, there is still some risk of "breakthrough" COVID infection when vaccinated. Doesn't this run counter to the idea of removing masks before herd immunity?

Herd immunity is a concept – we don't know exactly what level of vaccination is needed to achieve it and completely eliminate the virus. Most experts don't think we can fully eliminate this virus and that it will be endemic, or present in the population at some basic level, similar to the flu and other viruses. Vaccines approved in the U.S. do work against the variants that are emerging. That said, they are less effective, which is why it's important to vaccinate as many people as we can, as quickly as we can, to get the virus to a manageable level.

What's the risk of someone who gets COVID-19 when vaccinated sustaining "long COVID"?

So far, it looks like the risk of long COVID in vaccinated individuals is very, very low based on the data we have from thousands to millions of people. It is still possible, and in the few people where that happens, it may be due to immune system differences that we're still learning about.

For people who get COVID-19, develop long COVID, and then get vaccinated, we're seeing some evidence that getting the vaccine can help. We're not sure why that is yet, but one theory is that individuals with long COVID may continue to harbor the virus in the body after the initial infection, and the vaccine helps fight it.

Do we know any more about how long immunity lasts? Is it possible that we'll need booster shots in a number of months?

We are collecting data that shows a strong immune system response that goes out pretty far from the original vaccination, but we're only a year or so into this pandemic and can't be sure of exactly how long immunity lasts yet. However, mRNA vaccine platforms lend well to making boosters, so we are set up to produce them.

Personally, when would you feel comfortable not wearing a mask in a crowded indoor function?

I'll continue to wear a mask until we see the follow-up from summer holiday weekends, where people will likely wear fewer masks but many more will be vaccinated. In the fall, we should consider masking as it's a good way to prevent the flu and other seasonal viruses. Our immune systems will be tested more during fall and winter by spending increased time indoors and coughing from other viruses. We've seen in Asia that masking has helped stop pandemics earlier, so I am hopeful that we may adapt to wearing masks during higher-risk time periods and situations

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