As bizarre as it might sound, there may actually be a connection between online candle reviews and the next wave of Covid-19.
Initial claims about a link between Yankee Candle reviews on Amazon and a rise in cases of Covid were posted on Twitter and later explored on the platform during the Omicron surge in December 2021.
Twitter user @drewtoothpaste took screen grabs of one-star reviews of Yankee candles that were all made within a week of each other. Most reviews complained of "no scent" or "no smell" to their burning candles.
After seeing several of the tweets about this unlikely connection, Nicholas Beauchamp, associate professor at Northeastern University in the department of political science and the Network Science Institute, decided to formally test this hypothesis.
"It's interesting how it sort of progresses from joke to dabbling to 'I guess I'm doing this seriously,'" Beauchamp told CNBC Make It.
'The reviews were leading and the Covid cases were lagging'
In December of 2021, Beauchamp was actively working on a project, observing how social media could be used to inform Covid-19 data.
He also developed an interest in Covid's symptom of anosmia, or loss of smell.
This inspired him to investigate anosmia's potential link to reviews of scented products and determine if they could in fact be used as a way to predict Covid waves in the future.
"What I found in the original analysis [in December 2021] was that Covid cases predicted negative reviews, but not really vice versa, which implies, possibly, that it actually is people complaining because they might have anosmia," Beauchamp says.
"When I did it in June [2022], what I found was that it had sort of reversed a bit," he notes. "The reviews were leading, and the Covid cases were lagging. But the reviews really were kind of predictive of the cases going up and down."
In Beauchamp's paper, he analyzed nearly 10,000 Amazon reviews and was able to determine that negative reviews weren't linked to specific seasons where Covid cases typically rise and fall — like winter and summer.
He also looked at reviews about perfumes and found a similar connection.
Another consideration was the link between negative scented product reviews and cases of the flu, and there wasn't a correlation there, he notes.
Can candle reviews actually predict the next Covid surge?
This October, a doctor shared a Twitter thread that went viral about negative Yankee Candle reviews rolling in and the possibility of another Covid surge approaching.
But, "when I revisited it again a couple of days ago, for the first time the reviews and the Covid cases are really kind of dramatically diverging," says Beauchamp.
"The complaints have been going up for the last few weeks, and the case counts continue to go down over the last couple of months. So, something is going on that's kind of breaking this relationship."
There are multiple factors that may be contributing to this change, he notes.
Initially, the reviews were used as an unconventional way to track if people were suffering from loss of smell because they may have been unconsciously admitting that they were dealing with anosmia.
However, many became aware of this hypothesis and began adding disclaimers to their reviews in January that stated they didn't have Covid-19.
Additionally, the Centers for Disease Control and Prevention shifted from daily updates of Covid-19 cases and deaths to weekly reports. "In case you're wondering why I'm resorting to Amazon reviews as a source for near-real time COVID data," Jorge Cabarello shared in a tweet about how the agency's shift affected his methods for tracking Covid case numbers.
Beauchamp adds that experts believe people are not reporting positive cases as often as before, especially with the new reliance on at-home testing.
"What's kind of interesting this time around is that more of the people making these comments are actual medical professionals instead of random people on Twitter," Beauchamp says.
"I think the reason they're picking this up as a possibility is because they're sort of treating this as an indicator that we've hit rock bottom."
And though he doesn't think tracking negative candle reviews is a perfect method, he believes it may be helpful context for public health experts to take a closer look at more official indicators like wastewater surveillance.
"I still don't recommend that anyone actually use the candle indicator – but, I think that there's a serious need among the health professionals who do care about this to sort of draw upon these more indirect measures because that's all we've got at the moment."
Sign up now: Get smarter about your money and career with our weekly newsletter
Don't miss:
