Anthony Fauci, the U.S. government’s top infectious-disease expert, said he suffered mild side effects after receiving a second dose of the Covid-19 vaccine.

“I was hoping that I wouldn’t get too knocked out. I did for about 24 hours. Now I’m fine,” he said at a White House event Thursday.

Fauci, an adviser to President Joe Biden on Covid-19, said he felt fatigued and achy, “not sick.”

The mild side effects are consistent with what vaccine manufacturers reported in their clinical trials and are signs of the body’s immune response to the inoculation.