Daily Briefing

Covid-19 cases are on the rise again (and likely being undercounted)


According to data from the Johns Hopkins Coronavirus Resource Center, Covid-19 cases are more than six times higher than they were a year ago—and experts say that with the rise of at-home Covid-19 tests, case counts are likely being undercounted more than ever before.

Covid-19 cases are rising (and being undercounted)

Data from Hopkins shows a seven-day average of 119,725 Covid-19 cases as of Saturday, compared with 17,887 on May 28 of last year. However, despite rising case counts, Covid-19 death rates are lower than last year. As of Friday, the seven-day average of Covid-19 deaths was 470, compared with 637 on the same day last year.

According to Jason Salemi, an associate epidemiology professor at the University of South Florida College of Public Health, three factors are contributing to an undercount of Covid-19 cases: The increased availability of at-home tests, an overall decline in testing rates, and the fact that cases are generally milder because more people are vaccinated and many current variants cause less severe disease.

Currently, we're seeing "probably as much of an undercount as we've ever had during the pandemic," Salemi said.

Undercounts are nothing new, as experts say Covid-19 cases have likely been undercounted from the start. "We saw early on—in March 2020—that maybe one in 10, maybe one in 12 infections were actually being captured," said Jeffrey Shaman, an infectious disease specialist at Columbia University.

Shaman's research estimates that, at the end of 2020, one in four Covid-19 cases were being counted, and during the omicron surge, one in six cases were being counted. Now, Shaman estimates the real number of Covid-19 cases could be eight times higher than current case counts.

According to Gigi Gronvall, a senior scholar at the Johns Hopkins Center for Health Security, this is a consequence of having more at-home tests available.

"For people to have that information at their fingertips to be able to get the results that they need so that they can act on them immediately—that's totally worth it," she said.

Washington Secretary of Health Umair Shah agreed. "If I'm going to try to trade off, what's better? For me to know all the numbers or for me to have people empowered to make good decisions?" Shah said. "I would trade off to make sure people are empowered to make good decisions."

What this means going forward

Katelyn Jetelina, an adjunct professor at the University of Texas Health Science Center, said it's not ideal having so much uncertainty about Covid-19 case counts, but added that this summer might not see the same crisis-level surge as in years past.

As the weather warms up and people spend more time outside, "transmission is a lot less because of the ventilation outside," Jetelina said. In addition, given the surge of people infected with omicron, "we just have such high levels of infection-induced immunity that we have a very high immunity wall," she added.

Given that level of immunity, Maciej Boni, a professor of biology at Penn State's Center for Infectious Disease Dynamics, said it makes sense for policymakers to wait on reinstituting Covid-19 restrictions.

"The reason is that we're going to exhaust people's patience and potentially exhaust certain health resources [and] political capital that we want to have saved up for when we really need it," he said.

However, Melanie Ott, director of the Gladstone Institute of Virology, noted that the level of public immunity doesn't mean the unvaccinated should feel protected. "You should not think, 'Oh, I had omicron, I don't need any shots' or 'I don't need any more shots,'" she said. "We are going into a surge of the omicron subvariants that are more and more able to infect people who have preexisting immunity."

Given that case counts are being undercounted, experts recommend analyzing additional pandemic measures, including hospitalizations, the number of people on ventilators, the number of patients in the ICU, deaths, and wastewater data, as well as keeping tabs on what variants are circulating, to make informed precaution decisions.

Zinzi Bailey, an epidemiologist at the University of Miami, recommends relying on Covid-19 hospitalization data to get an idea of how prevalent the virus is in your community.

"I look at my local hospitalizations, and if they're starting to tick upwards, I modify my behavior accordingly—I'm going to be taking a little bit more attention in terms of masking, I'm going to be paying a little bit more attention about what indoor spaces I'm choosing to be in and how often I'm going to do that," she said.

Jetelina said she looks at trendlines in case counts to make decisions for her family. "My ears start perking up [when there's] anything over a 50-75% increase in the past two weeks," she said. When looking at case trends, if the line is "just starting to slowly creep up, then fine, but if the acceleration is getting faster and faster, that's when something seems up to me," she added.

In addition, immediate social networks often provide transmission clues. "If you're hearing your friends and your co-workers get sick, that means your risk is up and that means you probably need to be testing and masking," said Samuel Scarpino, VP of pathogen surveillance at the Rockefeller Foundation’s Pandemic Prevention Institute. (Simmons-Duffin, "Shots," NPR, 5/27; Nirappil et al., Washington Post, 5/28; Beals, The Hill, 5/29; Nyce ,The Atlantic, 5/29)

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