A US judge has upheld the University of California's Covid-19 vaccine requirement against a challenge by a professor who alleged he had immunity due to a prior coronavirus infection, in what appears to be the first ruling on the issue, reports Reuters.

US District Court Judge James Selna in Santa Ana, California, said the university system acted rationally to protect public health by mandating the vaccine and not exempting individuals with some level of immunity from an infection.

Selna's ruling denied a motion for a preliminary injunction by the professor, Aaron Kheriaty. And while Selna said the professor at the University of California, Irvine School of Medicine did not show a likelihood of success, Kheriaty said he plans to continue the litigation.

He told Reuters he plans to use the discovery process to determine how the policy was formulated and to question the university's expert witnesses about their reasoning for rejecting his arguments on natural immunity.