It’s a pox virus. The vehicles may change, but it’s related to other pox viruses like smallpox. Primarily through skin contact, which can include sex. The fact that it’s spreading through children is a bad sign, though, as schools are a big vector.

“Sex is probably the primary driver, and then the secondary driver is close contact and households,” said Dr. Jay Varma, the chief medical officer at SIGA Technologies, which manufactures tecovirimat, a drug used to treat mpox infection.