There’s a new wave of bad Yankee Candle reviews on Amazon. Does that tell us anything about COVID trends?

A new wave of Yankee Candle reviews on Amazon complains the products lack scent. Does that suggest another COVID-19 surge is imminent? It’s hard to say, but with official case reports increasingly an undercount, people are looking to other forms of information to gauge trends.

Jorge Caballero, a San Francisco Bay-based anesthesiologist who has tracked coronavirus-related trends on his popular Twitter account, tweeted screenshots Sunday of recent one-star Amazon reviews for Yankee scented candles, and asserted, “Yankee Candle reviews indicate that COVID is about surge again.”

His tweet quickly went viral, with more than 150,000 likes and retweets. No surge is happening right now, but experts have been predicting an uptick in cases in the cooler months. Caballero says elements like the Yankee Candle reviews — while not a local or definitive indicator — may provide insight into how good or bad things are looking.

The theory that consumers not being able to smell scented candles can serve as an indicator of a COVID-19 wave isn’t new, but it hasn’t been studied much.

One study by Nick Beauchamp — a West Philly native and an associate professor of political science and network science at Northeastern University in Boston — published by the Association for the Advancement of Artificial Intelligence earlier this year suggested that COVID-19 waves could predict poor scented candle reviews, with the caveat that there’s no evidence suggesting the reviews are a “leading indicator” of rising rates.

“‘No smell’ reviews do indeed reflect changes in U.S. Covid cases even when controlling for the seasonality of those reviews,” Beauchamp’s paper summary says. “These results suggest that inadvertent digital traces may be an important tool for tracking epidemics.”

With the omicron variant, Beauchamp and Caballero say, bad Amazon reviews may also help predict looming case surges, though updated data indicate any link may be weakening. It’s also difficult to definitively tie Amazon reviews with case increases — and cases don’t increase uniformly nationwide.

One of COVID-19′s most distinctive symptoms is the loss of smell. Even after recovering from COVID-19, some people continued to report not being able to smell for months. Since 2020, people on Twitter joked that one-star Amazon reviews for scented items — including candles and perfume — might be a clue that someone unknowingly had COVID-19.

Scientists, researchers, and tech-savvy spectators began to try to quantify the Amazon reviews.

Kate Petrova, a Ph,D, student at Stanford’s Psychophysiology Laboratory, published a string of data visualization sets and takeaways in a 2020 Twitter thread, noting that since the beginning of 2020, the proportion of scented candle reviews that mentioned a lack of scent grew from less than 2% to nearly 6%.

“These numbers may not seem like much, but the trajectory of no-scent reviews over the last 11 months is certainly an interesting one,” she said.

Beauchamp used a Google Chrome extension to grab nearly 10,000 Amazon reviews of the four top-selling Yankee Candles between 2018 and 2021. From there, he calculated the percentage per week of reviews mentioning “no smell” or “no scent,” compared with the number of weekly reported U.S. COVID-19 cases throughout the pandemic.

According to Beauchamp’s research, before the omicron variant, “no smell” reviews would follow already-documented spikes, holding less value from a public health perspective than if they could predict forthcoming spikes.

But after omicron became widespread, the reviews gave a “slight heads up,” Beauchamp said. Now, there’s divergence again.

“While reviews are still predictive of cases, that effect is weakening,” he told The Inquirer. “In the last few weeks, [reviews vs. case reports] have dramatically diverged, with ‘no smell’ reviews rising while official case counts continue to fall.”

Beauchamp noted that since he’s not an epidemiologist, it’s not appropriate for him to definitively say how well candle reviews reflect the state of the pandemic.

On Twitter, Caballero said Yankee Candles are an easy way to “spot-check” trends because Amazon groups reviews for the different candle scents together, making it easier to look at a larger sample size.

Some recent Yankee Candle reviews show the trend. A one-star review published Sunday for the spiced pumpkin candle mentioned “no scent.” One Saturday said the candle’s scent was “barely noticeable.” Three others published Saturday said the vanilla cupcake candle had “no smell” or smelled “faint.”

A Yankee Candle spokesperson did not immediately respond to a request for comment.

Caballero says the reviews are concerning and pleaded with his followers to “mask up and get boosted.”

Examining scented candle reviews is one of many approaches to better understand and predict COVID-19 case surges. Notably, researchers have used indicators including checking sewers for viral fragments in fecal matter, as well as using Google Trends search data to predict waves.

The City of Philadelphia is using its sewage to monitor COVID-19 and just started releasing information from the program. But the gap between data collection and publication is long, hindering its usefulness.

» READ MORE: Testing sewage for COVID is providing valuable data, but Philly seeks to get faster results

Beauchamp says the collection of “indirect data sources” may become more valuable as the “official sources become more unreliable.” Agencies are releasing data less frequently, and at-home testing means many cases go unreported.

While no national surge has started to date, and cases have decreased in Pennsylvania and New Jersey over the last two weeks, experts say there are hints that a winter case spike may be on its way.

As the days get chillier, people are more inclined to stay inside with others, rather than at open-air spaces where COVID is less likely to spread. Infections are on the rise in European countries, which in the past has been a precursor to similar increases in the United States.

The bottom line, according to the guy who published a study on candle reviews?

“As traditional measurements and data sources have been cut back, I think people who care about tracking the still-ongoing pandemic are driven to consider more indirect data,” Beauchamp said. “Candle reviews are about as indirect as it gets, and even with reduced testing, traditional data such as case counts, hospitalizations, or wastewater measurements are probably more reliable.”