Your Local Epidemiologist

KATELYN JETELINA

SEP 5, 2023

Since the last BA.2.86 update, lab and epidemiological data have trickled in. Many of us took a big sigh of relief after seeing specific results over the weekend.

Here is your update.

Lab data
Three labs have already tested BA.2.86 in a petri dish. (The speed of scientific discovery for SARS-CoV-2 still amazes me). They found three main things:

Escapes immunity. As suspected, BA.2.86 can escape our neutralizing antibodies— our immune system’s first line of defense. We thought BA.2.86 would escape our antibodies ~10 times more than XBB (the most recent Omicron subvariant to sweep the U.S.), but it’s only escaping 2-3 fold. In other words, we can expect BA.2.86 to cause infections, but not as much as anticipated.

Source here
Infectivity. BA.2.86 has a more challenging time infecting our cells than XBB. The more difficult time it has getting into our cells, the better. (When a virus evolves, there are typically tradeoffs—it gets better at one thing but at the expense of another. It seems that BA.2.86 traded infectivity for antibody escape.)

Previous XBB infection helps protect against BA.2.86. This news is very reassuring for our fall vaccines, as the updated formula includes XBB.

All good news. But, of course, what happens in a well-controlled lab doesn’t always reflect what happens in the real world. So, it’s essential to look at epidemiological data, too.

Epidemiological data
We continue to find cases of BA.2.86. The latest count is 39 samples in 10 countries. Wastewater systems have also detected BA.2.86 in the U.S., Switzerland, Thailand, and Spain. This means BA.2.86 isn’t a random blip on our radar and is spreading.

Our biggest question is around “growth advantage”: How quickly is it spreading? Especially in the current landscape of high immunity? This will give us an idea of the timing and height of a BA.2.86 wave. Unfortunately, determining this is incredibly challenging today because we need enough cases in the same country, but our surveillance is down 90%.

But three brave souls have given it a shot:

Weekly growth rate: 41% to 86% by Alex Selby

Weekly growth rate: 35% by Nick Rose

Daily growth rate: 21% by Oliver Johnson

These initial estimates suggest that BA.2.86 isn’t spreading as fast as the original Omicron (which had a weekly growth rate of 400%) but faster than XBB. In other words, we won’t have a tsunami, but a BA.2.86 wave is possible.

This can change. These estimations have a ton of limitations and we just don’t have a lot of data points to go off of. And like we’ve seen before, a variant can gain or lose speed over time. Delta, for example, started really slowly in the beginning before taking off.

Number of Delta cases over time. Figure Source: Marc Johnson
Other questions
We’ve started getting answers about how well our tools work against BA.2.86, too:

Paxlovid: Works

Antigen tests: Works

Monoclonal antibodies: Don’t work (but they also don’t work against XBB)

We still have unanswered questions:

Where did it emerge?

How did it emerge?

Does it spread faster in some places but not others?

Does it cause more severe disease? We don’t think so, but it would be nice to see data.

Bottom line
BA.2.86 has a ton of mutations, but the initial puzzle pieces look reassuring. We are at the mercy of time to see how this unfolds.

None of this changes the bigger story arc, though: SARS-CoV-2 continues to mutate and continues to cause illness and death. In fact, we are currently in a wave right now from Omicron subvariants. Regardless of what BA.2.86 does, our work for the fall/winter is already cut out. At the very least, get a COVID-19 vaccine this fall.

Love, YLE

“Your Local Epidemiologist (YLE)” is written by Dr. Katelyn Jetelina, M.P.H. Ph.D.—an epidemiologist, wife, and mom of two little girls. During the day, she is a senior scientific consultant to several organizations. At night, she writes this newsletter. Her main goal is to “translate” the ever-evolving public health world so that people will be well-equipped to make evidence-based decisions. This newsletter is free, thanks to the generous support of fellow YLE community members. To support this effort, subscribe below: