In a sharply worded dissent, Justice Clarence Thomas expressed support Thursday for a debunked claim that all Covid vaccines are made with cells from “aborted children.”

His dissent came in a decision by the Supreme Court to not take up a legal challenge by New York health care workers who opposed the state’s vaccine mandate on religious grounds.

Thomas, citing the plaintiffs, wrote that the health care workers “object” to the state’s vaccine mandate “on religious grounds to all available COVID–19 vaccines because they were developed using cell lines derived from aborted children.”

Pfizer and Moderna used fetal cell lines early in their Covid vaccine development to test the efficacy of their formulas, as other vaccines have in the past. The fetal tissue used in these processes came from elective abortions that happened decades ago. But the cells have since replicated many times, so none of the original tissue is involved in the making of modern vaccines.

So it is not true that Covid vaccines are manufactured using fetal cell lines, nor do they contain any aborted cells. 

Rather, the vaccines contain messenger RNA — genetic material that instructs our cells to make proteins, which then train the immune system to fight off the coronavirus. They also include fatty substances called lipids that help RNA cross our cell membranes, as well as salt, sugar, and a few substances that help stabilize the other ingredients.

In defending its vaccine mandate, lawyers for New York also noted that laboratory-grown stem cells, which derive from cells collected from a fetus nearly 50 years ago, were also used for testing the rubella vaccine.