AUDIE CORNISH, HOST:
By now, many Americans know someone who's been fully vaccinated but still got a breakthrough infection of COVID-19. To be clear, the Centers for Disease Control and Prevention still says that these cases are uncommon and only a tiny percentage of those uncommon breakthrough infections require hospitalization. But back in May, the CDC stopped tracking breakthrough infections unless they were severe. And that was before the highly contagious delta variant drove a new surge of COVID-19 throughout the country. So is this still the best practice? Well, vaccine expert Saad Omer joins us now. He's also the director of the Yale Institute for Global Health.
Welcome back to the program.
SAAD OMER: My pleasure.
CORNISH: The CDC had previously said that it makes sense to focus their efforts on the people who get very sick or who pass away from the disease, but critics say you need the full picture. So what is it that could be learned from tracking non-severe breakthrough infections?
OMER: In this pandemic, unfortunately, we have been chasing the outbreak. And the way to control an outbreak is to get ahead of it. And one way to get ahead of it is to detect these early signals and making sure that you are testing not just severe cases that take time to sort of get to the hospital. You are ahead of the outbreak by tracking at least a significant proportion. A random sample is helpful. CDC has said that they have - they're not - they haven't abandoned it altogether and they have these smaller studies on outbreak investigations. But from my perspective and some other experts' perspective, it is not insufficient to give us an early, complete, robust picture of things that we are not expecting. It's the unknown unknowns that get us.
CORNISH: How reliable a data point would it be? Do we know enough people who have a breakthrough infection even sort of bother to report it if it's not severe?
OMER: Well, that's why God created epidemiology. There are methods for sort of accounting for these biases. The bottom line is that we need to expect the unexpected. And one way of doing that is to follow these non-severe breakthrough cases as well.
CORNISH: Is it accurate, then, to say that breakthrough infections are uncommon?
OMER: It is accurate to say. They are far, far less common in terms of the proportion of vaccinated.
CORNISH: But how do we know? Like, if we've just said they're not - you know what I mean? - really tracking, then how can we say that?
OMER: Well, fortunately, other countries are tracking it. And even the imperfect data that is there suggest that, you know, they are far less common in the vaccinated versus unvaccinated. And so that continues to give us, at a smaller scale, some idea.
CORNISH: Those of us who do not have medical degrees, what are data points that make sense to pay attention to right now?
OMER: That's a good question. And one of the data points is the effectiveness of the vaccines going forward. And CDC is entirely accurate in saying that these vaccines continue to work. The other thing is to understand that, look, outbreaks are inherently dynamic. Recommendations will change, so pay attention to your local rates. Being - having that situational awareness, having that tolerance for the guidance to evolve and to be responsive to the outbreak and the epidemiology of the virus is incredibly helpful.
CORNISH: Saad Omer is the director of the Yale Institute for Global Health. Thank you for speaking with ALL THINGS CONSIDERED.
OMER: My pleasure. Transcript provided by NPR, Copyright NPR.