Elon Musk said on Monday he had “supposedly” tested positive for Covid-19, with no major symptoms.

“I supposedly have it again (sigh), but almost no symptoms,” the Tesla and SpaceX billionaire said in a tweet.

He also said “Covid-19 is the virus of Theseus. How many gene changes before it’s not Covid-19 anymore?”

In philosophy, the Ship of Theseus is a thought experiment that asks if something is the same thing after all its components have been changed.

Coronavirus variants have emerged throughout the two-year pandemic. According to Johns Hopkins University, more than 976,000 people have died in the US from Covid-19. Case numbers have dropped but officials have warned of possible rises fueled by variants or subvariants.

In November 2020, Musk questioned the accuracy of Covid-19 tests after claiming results showed he tested positive twice then negative twice on the same day.

Musk then said he “most likely” had a moderate case of Covid-19. He did not mention whether the results were from polymerase chain reaction tests, which are more accurate than rapid tests.

Musk was recently seen dancing and joking with fans as he oversaw the handover of Tesla’s first German-made cars at its Gruenhide plant last week.

Tesla’s Shanghai factory will be closed for four days after the city said it would go into a lockdown for nine days to test residents for Covid-19, as cases surge in China.

The plant is critical to Tesla’s exports and delivered more than 56,000 cars in February, or more than 2,000 cars a day.

Tesla has hiked prices of its cars in the recent past, citing inflationary pressures, and has said it would not launch new models this year due to supply-chain headwinds.