It's not mutually exclusive. If a company has H-1B quota that is unused, it may be beneficial for the company to sponsor under the H-1B directive rather than start a new process for an O-1. O-1s are also significantly difficult to qualify for; it is unclear whether an "average" public health expert would qualify.

O-1 didn’t exit back then.

Gotcha. The H-1B was first created in the 1950s for aliens of "distinguished merit and ability". In 1990, it became a visa for workers in a "specialty occupation". The 1990 law also added the O-1 visa.[1] It sounds like the H visa was rebadged as the O visa and a new skilled worker visa was named the H visa.

1. https://en.wikipedia.org/wiki/H-1B_visa#Creation

> Gotcha. The H-1B was first created in the 1950s for aliens of "distinguished merit and ability".

No it wasn't (as your own link clearly states), the H-1 was created in the 1950s, but the the H-1B was created in the 1990 INA, along with statutory dual intent for the H-1 category, and along with the creation of the O-1.

Sheesh ok. The H visa was created in the 1950s. Happy?

O-1 requirements are very strict, and it’s not enough to just be an expert on a random arcane topic X.