I hold a scientific visa for France (I am not European). Do I need some kind of health insurance to enter the country?

According to the *convention d'accueil*, the hosting institution is willing to take care of my health insurance. However, I am still in doubt because the contract starts two days after I plan to enter to France. The visa is issued valid from three days before the contract starts, so it will be valid when I intend to enter the country.