The amount of coronavirus found in wastewater from the Swedish capital has doubled in recent weeks and is now back at the same levels as in May, when peak results were recorded, the Royal Institute of Technology in Stockholm (KTH) has found based on weekly samples.
At the end of April and the beginning of May, the researchers found the highest levels of coronavirus in wastewater.
"We see similar, clear increases during week 39, at the end of September. The virus load is approaching the levels in May", KTH professor at SciLifeLab Cecilia Williams said in a statement.
As the number of coronavirus tests in the community spiked during August and September, the higher number of identified infected individuals was attributed to increased testing. However, the researchers believe that the increase in the number of COVID-19 cases is reflected in wastewater and thus doesn't depend on more people being tested.
"My interpretation is that this latest increase is definitely about an increased number of infected people in society", Cecilia Williams ventured.
This analysis is shared by fellow KTH researcher and senior lecturer Zeynep Cetecioglu Gurol, who suggested that the increase in COVID-19 cases isn't due to increased testing. Wastewater analysis allows for the detection of viruses at earlier stages, as it shows up in faeces before patients actually develop any symptoms.
KTH researchers went so far as to suggest a second wave in Stockholm, which many believe is already manifesting itself in many European cities.
"We see an increase that could be the beginning of a second wave in Stockholm. Virus levels have risen again, from being so low for a few weeks in July that we were unable to find them. Now the virus levels are back at almost the same high levels we saw last spring", associate professor and director of KTH Water Centre David Nilsson said in the statement.
Sweden has seen close to 95,000 COVID cases and nearly 5,900 deaths, most of them senior citizens. As its health authorities came up with conflicting messaging about the desirability of herd immunity, Sweden consistently avoided major lockdowns. When most of Europe closed schools, restaurants, gyms, and even borders, Swedes kept enjoying most of their freedoms. This unorthodox approach that some labelled "Darwinist" has since captured the world's attention, especially as it coincided with a much higher per capita death rate compared to Sweden's fellow Nordic countries.
State epidemiologist Anders Tegnell has since estimated that at least 20 percent of Swedes have had COVID-19, whereas Swedish Public Health Agency Director General Johan Carlson estimated the corresponding figure in Stockholm at 40 percent. However, the recent spike in cases in Stockholm has once again triggered questions about the very concept of herd immunity and its usefulness.