COVID Wastewater Levels Hit Year-High in Leuven

Coronavirus concentrations in Leuven’s wastewater have climbed to their highest level in a year, according to the Rega Institute at KU Leuven, raising fresh questions about whether SARS-CoV-2 is on the rise again in Belgium. The finding comes as national surveillance data from the Belgian public health institute Sciensano classified COVID-19 activity as “High” in its most recent weekly assessment.

In the Leuven wastewater, the virus had been barely detectable for an unusually long stretch. “We hadn’t seen COVID in the wastewater for four months. We’ve been tracking those figures for six years and it was the first time there was nothing to see. Now those figures are shooting up again across all of Belgium,” said Elke Wollants, lab manager at the Rega Institute, as reported by VRT NWS.

Why Wastewater Monitoring Matters

Wastewater surveillance has become a cornerstone of Belgium’s public health monitoring. The approach detects viral genetic material shed in feces by infected people, frequently before clinical case counts rise, making it a valuable early-warning system at a time when individual testing has declined sharply.

Belgium has been a pioneer in this field, launched by Sciensano with SARS-CoV-2 monitoring in September 2020. The program, which today covers 39 percent of the Belgian population across 172 municipalities and 30 wastewater treatment plants, was expanded in January 2024 to include influenza and RSV. Samples are collected every Monday over a 24-hour period from treatment plant influents and analyzed for all three respiratory viruses.

A Quiet Year, Then a Sudden Spike

The last clear COVID peak in Leuven was recorded in November 2025. Concentrations declined to near-undetectable levels through an unprecedented four-month gap, before beginning to rise again in August 2026. That climb accelerated sharply in the weeks leading up to early October, coinciding with the start of the academic year and the onset of the respiratory season.

Nationally, the picture is consistent. According to Sciensano’s national dashboard, SARS-CoV-2 registered as “High” as of the latest sampling date on Monday, 21 September 2026, while both influenza and RSV remained at “Low” activity levels. The next scheduled update was set for Monday, 5 October.

Wollants said the timing of the increase was expected. “With influenza we know when the season will start. With COVID we don’t quite know that yet. We have seen high peaks in summer too, but over the last two years it has started to normalize,” she said. The virus does not yet follow the predictable seasonal pattern of influenza, though the past two years have seen peaks stretch from September into November.

A Call to Vaccinate Now

With concentrations still climbing, Wollants urged those in at-risk groups to act promptly. “If you want to get vaccinated, now is the moment. After the peak it won’t do much good anymore,” she said. Protection takes effect roughly two weeks after vaccination. The advice applies chiefly to pensioners, people with weakened immune systems, and other risk groups.

Wollants stressed that the rise is only the beginning and that the eventual height of the peak cannot be forecast. “The figures are only just starting to rise. We can never predict how high the peak will be. It’s also been years since that virus really circulated, so the antibodies are gone. There’s a reason why we have to vaccinate again every year,” she said.

She also pointed to the risk of long COVID, citing a large European study published in The Lancet that associated vaccination with a roughly 30 to 50 percent lower risk of long COVID at the population level. “People think COVID is a banal cold, but you just have to be unlucky enough to get long COVID. There are people who still can’t go back to work years later,” she told Leuven Actueel.

Debunking a Persistent Myth

Wollants also rebutted social media claims that high wastewater concentrations are caused by vaccination itself. The team’s PCR tests target the N-gene of SARS-CoV-2, a piece of genetic material that is not present in mRNA vaccines, which contain only mRNA for the spike protein and are rapidly broken down after administration. “Everything we measure in wastewater comes from circulating infections, not from vaccinations,” she said.

What to Watch

The virus has attenuated since the early pandemic and is no longer as pathogenic as it once was, though it can still cause serious illness. “I hope not,” Wollants replied when asked whether Belgium could return to 2020-type conditions. “The virus has also weakened. It is no longer as pathogenic as it used to be, but you can still get very sick from it.”

Public attention now turns to Sciensano’s next national update on Monday, 5 October, which will show whether the upward trend in wastewater concentrations is sustained or accelerating. For now, health authorities are signalling that the window for vaccination before the peak is narrowing.