Outbreak Watch: August 28, 2026

When we last checked in on August 7th, the DRC had reported just under 4,000 confirmed cases of Bundabugio Ebola and about 1,800 deaths.

As of August 25th, that number climbed to 5,713 confirmed cases and 2,744 deaths, with 1,269 people recovered.

The outbreak now affects 58 health zones across six provinces.

The crude case fatality rate is about 48%.

So this isn't just the largest Ebola outbreak ever recorded in the DRC.

As measured by reported cases following recognition of the outbreak, it's being called the fastest-growing Ebola outbreak ever recorded.

But I want to clarify that.

Over the past several weeks, genomic analysis has given us a much clearer picture of what was happening before this outbreak was officially recognized, and a new analysis released this week strengthens that picture considerably.

The earliest genomic work, based on 139 Bundabugio virus genomes, suggested that the outbreak's common ancestor probably dated to around March, with uncertainty extending earlier.

But researchers now have a much larger dataset.

Their latest analysis began with more than 600 genomes, with 525 included in the principal time-calibrated reconstruction.

That analysis places the outbreak's most recent common ancestor around late February.

with a credible interval extending from mid-January through late March.

And importantly, that estimate has remained very stable as researchers have added hundreds of new genomes.

So we can now say with a lot more confidence that this outbreak was already underway well before it was officially recognized in May.

But the genomic reconstruction tells us something else that's important.

This doesn't appear to have been an explosive epidemic from the beginning.

The evidence instead suggests relatively slow initial growth.

probably centered around Mumbualu, followed by acceleration from March through June as the virus was exported into larger urban areas, including Bunia.

And that gives us some important context for the description we've seen attached to this outbreak, the fastest-growing Ebola outbreak ever recorded.

The extraordinary rise in reported cases after the outbreak was recognized is real, but that doesn't mean the virus suddenly became extraordinarily good at spreading.

In fact, the genomic researchers report no evidence of a fitness-altering mutation and no specific viral lineage taking over the epidemic.

Instead, we're seeing the outline of an outbreak that had been building basically unseen for months at first relatively slowly, then accelerating as it reached larger populations, and was already mostly established by the time the alarm was raised in May.

And there's another potentially encouraging piece of the genomic story.

Although cumulative case counts have continued to climb...