The mystery
On March 10, 2026, virologist Marc Johnson — a professor at the University of Missouri who studies pathogen evolution through wastewater — posted something striking:
The most prominent cryptic lineage in the world right now is from Lincoln, Nebraska. It's a B.1 infection (about 5 years old) that has been detected in their wastewater every week for about the last 18 months.
If that sentence doesn't immediately make sense, that's the point of this article. By the end, every word of it will — and it'll tell you something unsettling about how pandemics actually work.
Let's start from the ground up.
The family tree
The interactive diagram below is a simplified phylogenetic tree — a family tree for viruses. It shows how SARS-CoV-2 evolved from the original Wuhan strain in December 2019 into the variants circulating today.
Most branches sweep upward and to the right: Alpha, Delta, Omicron, and their descendants. One branch drops straight down, alone. That's the Lincoln variant.
Tap any variant to explore its story
Everything starts with a typo
To understand what you're looking at, you need one biological concept: mutation.
When a virus infects you, it hijacks your cells and forces them to make copies of its genome — a string of about 30,000 genetic "letters" (nucleotides). The copying machinery isn't perfect. Every time the virus replicates, it makes random typos — a letter swapped here, a letter deleted there.
Most typos are meaningless. Some are harmful to the virus and die out. But occasionally, a typo gives the virus an edge — maybe it binds to human cells a little better, or dodges an antibody a little more effectively. That version spreads. Natural selection does the rest.
This is how SARS-CoV-2 went from one strain in December 2019 to thousands of distinct lineages by 2026. Every branch on the tree above represents an accumulation of these copying errors, filtered by survival.
Branches on the tree
Scientists assign names to branches — lineages — based on shared patterns of mutations. The naming system works like a family tree:
B.1 was a dominant early branch in 2020. From B.1, further branches split off:
- B.1.1.7 (Alpha) — first major "Variant of Concern," identified in the UK in late 2020
- B.1.617.2 (Delta) — emerged in India, dominant by mid-2021, substantially more severe
- B.1.1.529 (Omicron) — appeared in late 2021 with ~50 mutations at once, a massive evolutionary leap
After Omicron, the naming shifted to a faster sub-lineage system: BA.1, BA.2, BA.5, XBB, JN.1, KP.2, and onward. But the principle never changed: mutations accumulate, branches split, natural selection picks winners.
Now here's the key detail: B.1 was a 2020 strain. In the wild, it was outcompeted and replaced years ago. Alpha replaced it. Delta replaced Alpha. Omicron replaced Delta. The world moved on.
So why is a B.1 descendant showing up in Lincoln, Nebraska's sewage in 2026?
Listening to the sewers
When you're infected with a virus — respiratory, gastrointestinal, or both (SARS-CoV-2 is both) — your body sheds viral particles in your feces. Every time you flush the toilet, fragments of whatever's replicating inside you enter the municipal sewer system.
Wastewater surveillance exploits this. Scientists collect samples of untreated sewage from wastewater treatment plants and sequence the viral RNA (ribonucleic acid — the virus's genetic material) they find in it.
The elegance is brutal in its simplicity:
- Every person in a sewershed uses the bathroom
- All those toilets converge to one collection point
- One sample captures a genetic snapshot of an entire city's infections
- Nobody has to visit a doctor or take a test
Wastewater surveillance doesn't care whether you have symptoms. It doesn't care whether you know you're infected. It doesn't care whether you'll ever get tested. It captures everything — including things nobody is looking for.
Nebraska's wastewater program, run by the University of Nebraska-Lincoln and the state health department, has been sampling since 2021. Their data has repeatedly detected emerging variants weeks before those variants appear in clinical testing. In Lancaster County (where Lincoln sits), wastewater signals have led clinical detection by as much as three weeks.
The ghost signal
Here's where it gets strange.
Normally, the lineages found in wastewater match the lineages found in clinical tests — nasal swabs from sick patients at hospitals and clinics. If Omicron is dominant in the sewers, Omicron is dominant in the hospitals. The two data streams agree.
A cryptic lineage is what happens when they don't.
A cryptic lineage is a distinct, often heavily mutated viral strain that appears consistently in wastewater sequencing but has never been found in any clinical sample. It's "cryptic" because it's hiding in plain sight — we know it exists because it's in the sewage, but we have no idea who is shedding it.
Marc Johnson's lab has been studying these since 2021. To date, his team has identified more than 20 cryptic SARS-CoV-2 lineages across the US. Some carry 4 to 24 amino acid substitutions — substantial evolutionary changes. Some have persisted in their respective sewersheds for over a year. Some carry mutations that revert to sequences found in bat coronaviruses, hinting at deep evolutionary pressures we don't fully understand.
The Lincoln variant is the most prominent of all of them. It's a B.1 descendant — a strain that branched off from the main evolutionary tree around 2020 or 2021 — and it has appeared in Lincoln's wastewater every single week for the last 18 months.
It has never been found in a nasal swab. Not once.
The patient you'll never meet
So who is shedding it?
A healthy immune system clears a COVID infection in one to three weeks. You get sick, you fight it off, you stop shedding virus. The infection ends.
But what if your immune system is severely compromised?
People with advanced HIV, organ transplant recipients on immunosuppressive drugs, patients on aggressive chemotherapy — their immune systems operate in a twilight zone. Strong enough to keep the virus from killing them. Too weak to eliminate it entirely.
In this state, the virus doesn't get cleared. It persists. It sets up a chronic infection — replicating continuously, day after day, week after week, month after month. And with every replication cycle, more mutations accumulate.
This is a fundamentally different evolutionary environment than normal transmission. In regular transmission, the virus has to be fit enough to spread from person to person. In a chronic infection, it just has to survive inside one body. The selection pressures are completely different. The mutations that accumulate are ones that help the virus evade that specific person's weakened immune response — not ones optimized for airborne transmission.
The result is a lineage that looks alien compared to the rest of the family tree. It's been evolving on its own island, accumulating mutations that no circulating strain carries, drifting further and further from everything else.
That is almost certainly what the Lincoln variant is.
Somewhere in the sewer catchment area of Lincoln, Nebraska, there is — with high probability — a single human being. They caught COVID-19 around 2020 or 2021, back when B.1 was still circulating. Their immune system could not clear it. For approximately five years now, the virus has been living and mutating inside their body. Every time they use the bathroom, millions of viral copies flush into the Lincoln sewer system. Every week, scientists detect them.
This person may not know they are the source. They may not even know they are chronically infected. Their identity is entirely unknown to public health officials.
Why Omicron should make you nervous
Here's the part that turns this from a curiosity into a warning.
Omicron — the variant that reshaped the pandemic in late 2021 — carried roughly 50 mutations compared to its nearest known relative. That's an extraordinary number. Normal variant-to-variant evolution accumulates mutations gradually, maybe a handful at a time. Omicron appeared with dozens, seemingly out of nowhere.
The leading hypothesis for where Omicron came from? A chronic infection. Exactly the same mechanism as the Lincoln variant.
The theory goes: somewhere in southern Africa, an immunocompromised individual (possibly someone with untreated HIV — the region has the world's highest HIV prevalence) caught an early COVID strain and couldn't clear it. Over many months, the virus mutated inside their body, accumulating dozens of changes. Eventually, it transmitted to someone else. That someone else spread it. And within weeks, Omicron was everywhere.
Chronic infections are variant factories. They give the virus something it doesn't normally get: time. Extended time inside one host, with a semi-functional immune system providing just enough pressure to drive evolution but not enough to end it.
The Lincoln variant has been evolving inside one person for roughly five years. That's far longer than the suspected Omicron incubation. It has accumulated mutations nobody has cataloged. If it ever transmits — if the chronically infected individual passes it to someone with a normal immune system who then passes it to others — those mutations could give it properties no current variant has.
Will it transmit? Probably not. Most chronically-evolved strains lose their ability to spread between people because they're optimized for one body, not airborne transmission. But "probably not" is not "definitely not." And the Lincoln variant is only the most prominent example. There are more than 20 known cryptic lineages, and those are only the ones detectable in the sewersheds that scientists are monitoring.
The lesson from the sewers
The Lincoln variant tells a story about our relationship with infectious disease that's easy to miss if you only follow case counts and hospitalizations.
Pandemics don't end cleanly. The virus doesn't disappear. It finds niches — immunocompromised hosts, animal reservoirs, populations with limited healthcare access — and it persists. In those niches, it evolves on its own terms, on its own timeline, under its own pressures.
Wastewater surveillance is one of the few tools that can see into those niches. It doesn't require the infected person to seek care, get tested, or even know they're sick. It just requires them to use the bathroom.
Right now, in Lincoln, Nebraska, a single anonymous person is flushing a five-year-old virus into the sewers. Scientists can detect it. They can sequence it. They can track its mutations week by week. But they can't find the person. They can't treat them. They can't stop the virus from evolving.
The ghost in the sewers keeps mutating. The tree keeps growing a branch that shouldn't exist.