The recent uptick in Covid-19 viral presence in Bengaluru’s wastewater isn’t entirely unexpected. It fits a pattern that scientists have quietly been tracking for the past two years — a recurring, low-profile wave that slips past most public radars.
Published Jun 03, 2025 | 7:00 PM ⚊ Updated Jun 03, 2025 | 7:25 PM
Researcher drawing water from STPs for wastewater surveillance (#COVIDActionCollab)
Synopsis: Wastewater surveillance data indicates an increase in Covid viral load across several regions. In recent weeks, the rise in viral presence across Bengaluru’s sewage treatment plants (STPs) has sparked comparisons with past polio detection incidents.
As India’s active Covid-19 cases rose to 4,026 on Tuesday, 3 June, wastewater surveillance data indicates a similar increase in viral load across several regions. Kerala is currently reporting the highest number of cases, with over 1,435 infections, followed by Maharashtra with 506 cases.
Commenting on the situation, Dr Rakesh Mishra, Director of the Tata Institute for Genetics and Society (TIGS), said, “The increase in viral load seen in wastewater aligns with the rise in reported clinical cases. It suggests a correlation between what we detect in the environment and what we’re seeing in terms of infections.”
Dr Mishra explained that direct comparison with clinical data is difficult due to limited testing. “There’s no easy way to compare this with clinical tests because very few are being conducted,” he said. “Most of the people shedding the virus are asymptomatic, so clinical systems often don’t detect what’s happening. However, wastewater analysis shows a clear increase. This tends to happen every few months — what we refer to as a ‘silent peak.’”
He elaborated, “Like the common cold, Covid-19 continues to cycle through populations, often going unnoticed unless someone is severely ill or tested. In fact, the last silent wave passed largely unnoticed in the general population, but we detected it through wastewater monitoring. Since wastewater analysis is not dependent on symptoms or testing rates, it provides a more accurate picture of viral spread.”
“In many cities, we are observing a general trend of increasing viral presence in wastewater samples,” Dr Mishra told South First.
In recent weeks, the rise in viral presence across Bengaluru’s sewage treatment plants (STPs) has sparked comparisons with past polio detection incidents, particularly in Kolkata, where vaccine-derived traces were once suspected. But experts say the current detections are of a different nature entirely.
Dr. Mishra, a leading scientist involved in genomic surveillance, dismissed the possibility of vaccine remnants being behind the recent uptick in virus traces. “No, no, no — these are not vaccine-related cases,” he said emphatically. “We know the genomic sequence of the variant being detected, and it is consistent with current Omicron sublineages like JN.1. This is active viral shedding from new infections, not residues from past vaccinations.”
He clarified that, while oral polio vaccines sometimes left genetic footprints detectable in wastewater, Covid-19 vaccines do not behave the same way. “The genetic material from Covid vaccines won’t remain in the body or get shed for more than a few days,” he said. “Vaccination for Covid happened years ago, so what we’re seeing now is definitely a new infection, not leftover vaccine RNA.”
When asked about the scale of the viral load being tracked in the city, Dr. Mishra said the positivity rate across tested STPs is nearly 100 percent. “Every sample we test is showing virus presence,” he noted. “We’re monitoring about 10 STPs in Bengaluru — out of 28 in total — and across all of them, the pattern is consistent.”
This indicates a city-wide dispersion of the virus, not limited to any specific cluster. “We’re seeing similar results in other cities — Vijayawada, Pune, Delhi, and so on,” Dr Mishra said. “So there’s no reason to assume that only certain parts of Bengaluru would be affected.”
While these findings don’t align exactly with officially reported case numbers, they do point to a rising trend in community transmission. “You can’t directly compare sewage data with the number of government-confirmed cases,” he explained. “The government isn’t testing as rigorously now — nor is that necessarily required — but our data clearly shows an increase in viral load over the past few weeks.”
However, Dr Mishra cautioned against panic. “These are what we call silent peaks,” he said. “They come and go quietly. As ICMR has pointed out, there are no alarming clinical symptoms being reported. Most cases are mild and manageable at home.”
Still, he urged the public to remain cautious and responsible. “If you have symptoms — a sore throat, mild fever — isolate yourself. Avoid crowds. Wear a mask, especially in crowded settings,” he advised. “Even someone without symptoms can spread the virus unknowingly, so basic precautions still matter.”
Dr Mishra added that the current variant’s evolution fits a predictable viral pattern: more infectious, but less severe. “There’s no evolutionary advantage for a virus to become deadlier,” he explained. “If people are bedridden, they don’t spread it. A virus thrives when it can move — and mild symptoms let it do that.”
His message: Stay alert, not alarmed. And when in doubt — mask up.
The recent uptick in Covid-19 viral presence in Bengaluru’s wastewater isn’t entirely unexpected. It fits a pattern that scientists have quietly been tracking for the past two years — a recurring, low-profile wave that slips past most public radars. These “silent peaks,” as experts call them, tend to emerge every six to seven months — and the current one is right on time.
“There’s no strict rhythm to it, but we typically see some increase in some region every six or seven months,” said Dr Mishra, one of the country’s leading virologists involved in wastewater surveillance. “The last time we saw something similar was between December 2021 and January 2022, and before that, in March 2023, which was the XBB.1.5-driven wave. Prior to that, we had peaks in the middle of 2022 and again toward the beginning of 2024.”
Each of these waves showed a clear correlation between wastewater viral loads and clinical testing data. “Whatever dates we’ve observed spikes in wastewater, clinical cases have also shown some rise,” Dr Mishra said. “So while these aren’t massive outbreaks, they do indicate increased transmission.”
Asked whether this means India is entering a phase where Covid becomes “seasonal,” like influenza, he offered a nuanced explanation.
“You can loosely call it seasonal — in the sense that we’re seeing waves every few months — but it’s not strictly tied to winter or weather,” he said. “With flu, for instance, the rise is quite predictable in colder months. But for Covid, we’re seeing increases even in summer. So it’s not just about temperature or humidity.”
Instead, the recurrence of these spikes is driven by three main factors:
“These factors combine, and in that window — usually every six or seven months — we see an increase in infections,” Mishra said. “And while many of these may not lead to clinical symptoms, they still show up in our wastewater data, because people are shedding the virus.”
So far, these silent spikes haven’t translated into major hospitalisations or health system strain, thanks to the largely mild nature of circulating variants like JN.1 and its offshoots. Still, the regularity of these waves suggests COVID is settling into an endemic rhythm — not entirely seasonal, but cyclical, driven by the complex dance between immunity, behaviour, and viral mutation.
“We’re no longer dealing with the unpredictable waves of 2020 or 2021,” Mishra concluded. “But we’re not done with the virus either. It’s still here — just quieter.”
(Edited by Muhammed Fazil.)
