The coronavirus pandemic certainly affected people's well-being. In a new study that used data from social media, researchers found that its impact on expressed sentiment was much worse than a bad Monday mood.

When the COVID-19 outbreak happened, it led to "emotional distress to citizens beyond those contracting the disease," the authors of a new study, published in Nature Human Behavior, noted. However, there isn't exactly a way to measure how it affected people's sentiments.

For their study, the researchers looked at the language used in 654 million geotagged social media posts from more than 100 countries from Jan. 1 to May 31, 2020. They found that COVID-19 led to "a sizeable drop" in expressed sentiment globally, which was especially apparent after the World Health Organization (WHO) declared it a pandemic on March 11, 2020.

By comparison, before the pandemic, people tended to post the most positive moods on social media during weekends and the most negative ones on Mondays, the Massachusetts Institute of Technology (MIT) said in a news release. The researchers even described Monday as "the unhappiest day."

At the onset of the pandemic, however, the sentiment was 4.7 times as large as the drop in sentiment from Sunday to Monday. Furthermore, the change was also larger than the sentiment change in response to extreme temperatures and natural disasters.

"This suggests that the acute impact of COVID-19 on sentiment is potentially more pronounced than that of extreme hot temperatures and climate disasters," the researchers wrote.

All the countries in the sample saw the change at the beginning of the pandemic, showing the "universality" of the sentiment change, the researchers noted. The biggest drops in sentiment were observed in Australia, Spain, the U.K. and Colombia, MIT noted. On the other hand, the countries least affected were Bahrain, Botswana, Greece, Oman and Tunisia.

The researchers also had other interesting findings. For one, they found that the lockdowns didn't affect the public mood much.

"Our analysis implies that lockdown policies do not necessarily entail a trade-off between physical health and emotional well-being — at least not for the average population of a country," the researchers wrote.

"On the one hand, lockdown policies might make people feel secure, and not as scared," Siqi Zheng, MIT professor and study co-author, said in the university news release. "On the other hand, in a lockdown when you cannot have social activities, it's another emotional stress. The impact of lockdown policies perhaps runs in two directions."

The researchers also looked at how long it took the countries to recover from half of this drop in sentiment and found that it varied from 1.2 days in Israel to 29 days in Turkey.

"It is important to mention that the recovery time not only reflects the emotional resilience towards the pandemic itself," the researchers wrote. "This measure should be interpreted as a combined effect of pandemic severity and regulatory policies, and it may be influenced by other events happening around the first wave of the pandemic within each country."

The researchers noted that their work shows how social media could be used as a tool to determine "real time measurements of affective states." It also adds to the list of studies showing the impacts of the pandemic on people's well-being.

For instance, a new survey by the American Psychological Association found that school personnel has been experiencing violence, threats and harassment from students during the pandemic, noting that it may be a result of the isolation that the children and teens experienced.