Gilead Sciences Inc.’s experimental twice-yearly shot prevented 100% of HIV cases in women and adolescent girls in Africa, the first successful big trial of what’s hoped to become a powerful new drug regimen for fending off the virus.Gilead hopes its new long-acting shot lenacapavir will provide an easier-to-use option compared to other HIV prevention drugs that are either daily pills or must be injected every two months. The two yearly injections could be done at regularly scheduled doctor visi...