Last week, the Centers for Disease Control and Prevention (CDC) held a conference at a hotel in Atlanta. Its objective: to highlight the work of its trainees in applied epidemiology, who for the past year have investigated public health topics ranging from cancer to avian flu and infant mortality.
This year, the CDC hosted 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, the organizers were informed that several participants had tested positive for Covid-19. As of May 2, 35 cases were linked to the conference, according to a CDC representative.
I attended the middle two days of the conference in person and on Tuesday I received an email notification regarding the cases. The email also said the CDC and the Georgia Department of Health were conducting a “rapid assessment” to understand the dynamics of the outbreak, and asked me to complete a survey that would be sent to me.
News of the event was encounter some schadenfreudewith several commentators scoffing at the irony: an agency whose Covid response was seen by many as a failure had itself been subject to an outbreak of infection.
Contempt 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 the risks of Covid-19 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 at the start of the pandemic. Due to changes in the virus itself and due to high rates of community immunity to Covid-19 due to infection or vaccination, transmission is now occurring less rapidly. More recent waves of infection have been smaller and have resulted in more asymptomatic infections and fewer serious consequences than before.
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 through home testing, or aren’t tested at all.
But the virus is clearly still circulating and large gatherings still increase 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 contexts?
The answer to this question probably varies considerably.
Early last summer, conferences around the world meeting in person for the first time since 2020 led to outbreaks of Covid-19. Although some of the conferences involved required proof of vaccination to attend, few made screening efforts at gatherings, and many did not require masks.
Few conference organizers bothered to trace infections among attendees, but the infections were there. In a comment last December in the review Nature, Swiss scientist James Kirchner, who contracted 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% respondents.
Although many conferences may be the sites of Covid-19 outbreaks, public health conferences might be more likely to be aware of these outbreaks and send messages about them, simply because of who they are. organize and attend. It’s unclear how the CDC identified the cases among last week’s conference attendees, but it wouldn’t be surprising if a conference by and for disease sleuths took a particularly proactive approach to case finding. — and whether its attendees were more likely to self-report cases than people attending other conferences.
There’s actually an epidemiological term for this: detection bias, which occurs when different groups collect outcome data differently. Given the audience of a CDC conference and its priorities, it is more likely that the transmission of Covid-19 taking place there would be detected than at a conference for different types of professionals.
In an email, Kirchner told me that other conference organizers have told him they specifically avoid testing attendees for Covid-19 because it’s bad for local tourism. This suggests that, on the whole, people see the spread of the virus at mass gatherings as a deterrent to attending such gatherings.
But it’s not clear that these considerations really change people’s decisions to attend big events. And moreover, it is not clear that they should.
2) Community outbreaks no longer cause the same damage as before
As of January 2022, public health officials say that community transmission of Covid-19 – that is, outside of hospitals, nursing homes, prisons and other institutions – is not no longer a valid measure of the harms of the pandemic. In this light, an outbreak at a conference simply seems less dangerous than before.
This is largely because many people are now generally at very low risk of injury from Covid-19 infection.
It’s not that the virus isn’t hurting anyone anymore – it is, albeit in much lower numbers than at the start of the pandemic. According to the CDC, nearly 600 people were hospitalized in the United States with Covid-19 infection in the week ending April 22. In the same week, there were 793 deaths in the United States involving the virus (the figure may change as new data comes in).
These are real misdeeds. However, they were largely concentrated in specific groups of people, either because of their age or because of a disability.
Look at the chart below, which shows hospitalizations by age group from March 2020 to now. In the week ending April 22, across the United States, 76 adults under the age of 50 were hospitalized with Covid-19 – about a year and a half per state, on average. The number was slightly higher – an average of 2 per state – for adults aged 50 to 64.
On the other hand, 400 people aged 65 and over were hospitalized during the same week. (It is unclear, however, what proportion of these older people lived in the wider community. A quarter of people over 65 hospitalized with Covid-19 through January 2022 resided in long-term care facilities. , such as retirement homes.)
It’s a different situation from, say, January 2022, when more than half of those hospitalized with Covid-19 were under the age of 65.
When it comes to this particular CDC conference, age differences in severity risk are significant. The conference is a kind of professional speed-dating event that matches incoming interns with agency training positions and graduating interns with public health jobs — so its attendees are typically younger.
Hospitalizations and deaths aren’t the only outcomes that matter: Long Covid is another potential infection-related harm. Here, too, there is reassuring news. Recent research suggests that people infected with SARS-CoV-2 are now less likely to develop prolonged symptoms than those infected earlier in the pandemic, especially if they are vaccinated or have previously been infected.
Almost all Americans have had the infection at least once, and there is no scientific consensus on the risk of reinfection with Covid-19, especially in otherwise healthy adults younger than 65. Many studies showing the harms of reinfection have examined the relatively high risk populations: the elderly and people who have had a first serious infection with Covid-19.
The bottom line is that while Covid-19 poses a higher risk to older and sicker people, the threat to others is actually quite low. And people who are at higher risk of getting an infection — or who are in contact with someone who is — can and often do self-select to avoid large gatherings, or take precautions to prevent infection. infection, such as masking and obtaining a bivalent vaccine.
We may be past the point where it is useful to obsess over the details of Covid-19 outbreaks among vastly younger and healthier populations. But it’s still productive to prevent transmission even among low-risk people when it’s not too cumbersome to do.
3) For many, the benefits of picking now outweigh the risks
Large in-person gatherings have advantages 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.
For many people, these benefits have long outweighed the risks of infection. Three years into the pandemic, an in-person CDC conference suggests the math is now also checking public health experts.
For the foreseeable future, attending mass events will carry Covid-19 risks – but that risk looks very different now than it did earlier in the pandemic. It is impractical to expect gatherings with others to have no infectious risk. Even public health institutions recognize this.