Middle school science teacher Kent Heckenlively has spent part of his time teaching, well, not science.

A prominent anti-vaccine campaigner, Heckenlively made world news in 2017 when he was denied entry to Australia for a lecture tour to encourage parents to stop vaccinating their children, according to the Australian Broadcasting Corporation. That didn’t blunt the California science teacher’s ambitions: Since COVID-19 hit, he’s been on a writing tear.

In April 2020 he released a bestselling book with co-author Judy Mikovits, a discredited scientist who claims that vaccines “kill millions.” Last October the pair released another book. That one questions mask use and alleges, among much else, that masks weaken the immune system by restricting oxygen intake – an idea not supported by the CDC or World Health Organization.