Last week, the Centers for Disease Control and Prevention (CDC) held a conference at an Atlanta hotel. Its purpose: showcase the work of its applied epidemiology trainees, who over the past year have investigated public health matters ranging from cancer to bird flu to infant mortality.
This year, the CDC held the conference in person for the first time since 2019 (they also offered a virtual attendance option). On April 27, the last day of the conference, organizers were notified that several attendees had tested positive for Covid-19. As of May 2, 35 cases were linked with the conference, according to a CDC representative.
I attended the middle two days of the conference in person, and on Tuesday, I received a notification email about the cases. The email also noted that the CDC and the Georgia health department are conducting a “rapid assessment” to understand the outbreak’s dynamics, and asked me to fill out a survey that would be sent my way.
News of the event was met with some schadenfreude, with several commenters jeering at the irony: An agency whose Covid response many viewed as a failure had itself been subject to an outbreak of the infection.
Scorn aside, there’s actually something to learn here. The outbreak says a lot about the current state of the pandemic, and how to think about Covid-19 risks right now.
Here are three big lessons.
1) If you look for Covid anywhere, you’ll find it everywhere — perhaps especially at large gatherings
Covid-19 infections look different and less severe now than they did earlier in the pandemic. Due to changes in the virus itself, and because of high rates of community Covid-19 immunity due to infection or vaccination, transmission now happens less briskly. More recent waves of infection have been smaller and led to more asymptomatic infections and fewer severe outcomes than in earlier times.
At the same time, US public health officials are identifying fewer cases than ever before. That’s because so many Covid-19 cases go unrecognized as asymptomatic, are diagnosed by home testing, or aren’t tested for at all.
But the virus is clearly still circulating, and large gatherings still raise the risk of transmission. There’s probably more Covid-19 circulating at big events than we realize — but are we looking for it in these settings?
The answer to that question probably varies widely.
Early last summer, conferences around the world reconvening in person for the first time since 2020 led to Covid-19 outbreaks. Although some of the conferences involved required proof of vaccination to attend, few deployed screening efforts during the gatherings, and many did not require masks.
Few conference organizers bothered to trace infections among attendees, but infections were there. In a commentary last December in the journal Nature, Swiss scientist James Kirchner, who acquired the infection at a conference earlier in the year, wrote that his “guerrilla” tactic of sending a self-created survey to attendees identified infections in 28 percent of respondents.
Although lots of conferences might be the sites of Covid-19 outbreaks, public health conferences might be more likely to be aware of those outbreaks, and send around messaging on them, just because of who’s organizing and attending. It’s not clear how the CDC identified cases among attendees of last week’s conference, but it wouldn’t be surprising if a conference by and for disease detectives had a particularly proactive approach to case-finding — and if its attendees were more likely to self-report cases than people attending other conferences.
There’s actually an epidemiologic term for this: detection bias, which happens when different groups collect outcome data differently. Given a CDC conference’s audience and their priorities, it’s more likely Covid-19 transmission happening there would be detected than at a conference for different types of professionals.
In an email, Kirchner told me organizers of other conferences have told him they specifically avoid looking for Covid-19 among attendees because it’s bad for local tourism. That suggests that, broadly, people see the spread of the virus at mass gatherings as a deterrent to attending those gatherings at all.
But it’s not clear these considerations are really changing people’s decisions to participate in large events. And furthermore, it’s not clear that they should.
2) Community outbreaks don’t lead to the same harms that they used to
Since January 2022, public health leaders have been saying that Covid-19 transmission in the community — that is, outside of hospitals, nursing homes, prisons, and other facilities — is no longer a valuable measure of pandemic harms. In that light, an outbreak at a conference just feels less dangerous than it used to.
That’s largely because many people are now generally at very low risk from being hurt by a Covid-19 infection.
It’s not that the virus is no longer hurting anyone at all — it is, although at much lower numbers than earlier in the pandemic. According to the CDC, 2.5 out of every 100,000 Americans were hospitalized in the US due to Covid-19 infection during the week ending April 22. The same week, there were 885 US deaths involving the virus. (The figure may change as new data trickles in; in prior weeks, weekly deaths were above 1,000.)
Those are real harms. However, they were largely concentrated in specific groups of people, either because of age or disability.
During the week ending April 22, across the US, 0.8 out of every 100,000 adults under 50 were hospitalized for Covid-19. The number was about two-and-a-half times as high — 2.1 per 100,000 people — for adults 50 to 64 years old.
In contrast, 11.2 of every 100,000 people 65 and over were hospitalized during the same week — nearly 14-fold the rate among adults 18 to 49. (It’s not clear, though, what proportion of these seniors were living in the wider community. A quarter of people over 65 hospitalized for Covid-19 through January 2022 were residents of long-term care facilities, like nursing homes.)
This is a different situation from, say, January 2022, when hospitalization rates for younger adults were higher overall, and also closer to those among older adults.
When it comes to this particular CDC conference, age differences in severity risk matter. The conference serves as a sort of professional speed-dating event that matches incoming trainees with training positions at the agency, and graduating trainees with public health jobs — so its attendees generally skew younger.
Hospitalizations and deaths aren’t the only outcomes that matter: Long Covid is another potential harm related to infection. Here, too, there’s some reassuring news. Recent research suggests people infected with SARS-CoV-2 now are less likely to develop prolonged symptoms than those infected earlier in the pandemic, especially if they’re vaccinated or have been previously infected.
Nearly all Americans have had the infection at least once, and there’s no scientific consensus about how much risk there is with Covid-19 reinfection, especially in otherwise healthy adults under 65. Many of the studies showing reinfection harms have looked at relatively high-risk populations: older adults and people who had severe first-time Covid-19 infections.
The upshot is that while Covid-19 does pose a higher risk to older, sicker people, the threat to others is actually quite low. And people who are at higher risk of harm from infection — or who have contact with someone who is — can and often do self-select to avoid large gatherings, or take precautions to prevent infection, like masking and getting a bivalent vaccine.
We may be past the point where it’s useful to obsess over the details of Covid-19 outbreaks among largely younger, healthier populations. But it’s still productive to prevent transmission even among low-risk people when it’s not overly burdensome to do so.
3) To many, the benefits of gathering now outweigh the risks
Large in-person gatherings have benefits that online interactions lack: They provide human connection and a sense of group identity, and especially for job seekers, make it easier to assess interpersonal compatibility.
To many people, those benefits have long outweighed the risks of infection. Three years into the pandemic, an in-person CDC conference suggests that the math now checks out for public health experts, too.
For the foreseeable future, attending mass events is going to have Covid-19 risks — but that risk looks a lot different now than it did earlier in the pandemic. It’s impractical to expect that gatherings with others will have no infectious risk. Even public health institutions recognize that.
Correction and clarification, May 5, 4:30 pm ET: A previous version of this story understated, in both the text and a graphic, the count of weekly Covid-19 hospitalizations in the US. The numbers previously used were obtained from a network of sentinel hospital sites, which represent approximately 10 percent of the US population; the story incorrectly represented these numbers as representing the entire US population.
The story has also been updated to add additional information on the lags in death data reporting.