You probably picture a lab that handles the deadliest viruses on earth as a remote outpost, far from houses, schools and traffic. Most of us never think about where these buildings actually sit. The map has quietly changed.
The world has 51 operational biosafety level 4 laboratories across 27 countries. That is roughly double the number a decade ago, with another 18 under construction, most of them in Asia.
Those figures come from the Global BioLabs Report, by researchers at King's College London and George Mason University. These are the labs that study Ebola, Marburg, Nipah and smallpox, pathogens for which there is no approved cure.
Three-quarters of these labs are in urban areas. That single fact is what has biosecurity experts worried. An accidental release in a dense city reaches far more people than one in open country.
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What a biosafety level 4 lab actually looks like
Biosafety level 4, usually shortened to BSL-4, is the highest containment level in laboratory science. Scientists work inside full-body positive-pressure suits with their own air supply.
The buildings themselves are engineered against leaks. They have sealed doors, filtered air, and multiple shower-out stages between the lab and the outside world.
A rare tour of the UK's Defence Science and Technology Laboratory at Porton Down, published by Forces News, described the layout plainly. Lower-risk pathogens sit on the outer ring of the building. The highest containment labs sit at the center.
The color red on a door or suit marks the zone where Ebola and Marburg are handled. Scientists must have at least two years of experience with less dangerous pathogens before they are allowed in. The actual engineering is strict and the people inside are specialists.
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Neither fact eliminates accidents.
Why urban locations change the math
Historically, maximum containment labs were built on isolated government reservations. The current wave is different. Many of the new facilities sit inside or next to major cities, including capitals with millions of residents nearby.
Gregory Koblentz, a biodefense expert at George Mason University who co-authored the Global BioLabs analysis, put it plainly. "Eighty percent are located in urban areas, which heightens concerns about accidents at these facilities," he said.
His coauthor Filippa Lentzos of King's College London echoed that in a statement released with the report.
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"There has been a global boom in construction of labs handling dangerous pathogens, but this has not been accompanied by sufficient biosafety and biosecurity oversight," she said.
The oversight gap experts keep flagging
Building a lab is one thing. Supervising what happens inside it is another.
A June 2025 commentary from RAND called laboratory biosafety and biosecurity a dangerous blind spot in global pandemic planning. The authors noted that the World Health Organization's Pandemic Accord barely addresses the threat of laboratory accidents.
The entire text mentions laboratory biological risk management only twice. RAND's authors recommended mandatory reporting of lab accidents and independent assessments of laboratory capabilities. They pointed again to the fact that three-quarters of BSL-4 labs sit in urban areas.
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The Global BioLabs analysis found that only seven of the 27 countries with a BSL-4 lab earned a good overall score for biorisk management.
Just one of the 27 has comprehensive national oversight for dual-use research, meaning experiments that could be misused to make a pathogen more dangerous.
Most of the planned new labs are in countries that score poorly on governance measures.
What good oversight looks like
The United States and the United Kingdom are frequently cited as reference points. In the US, the Centers for Disease Control and Prevention runs a federal Select Agent Program.
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The program regulates which labs can hold the most dangerous pathogens, who can access them, and how incidents must be reported. In the UK, Porton Down operates under the Health and Safety Executive's containment regulations, with routine inspections.
Neither system is perfect, and both have had publicized lapses. But both offer the layered structure that researchers say is missing where new BSL-4 facilities are being built.
These labs study the pathogens behind the worst outbreaks the world sees, including the current cluster of Ebola and Marburg outbreaks across Central and East Africa. The Global BioLabs tracker at globalbiolabs.org publishes the current count and oversight scores by country.
This article is made and published by Aksel Kryhlmand, who may have used AI in the preparation.