From the article, "A few months ago, I started a magazine assignment to answer some questions about SARS-CoV-2 and the immune system. I encountered paragraphs like this"... and the author links to this this [1] New Yorker article about COVID that was published November 2020. So from context clues, was probably published in late 2020.
(He says it was from his blog, but it's not actually in the blog.)