<prompt> tafsiri zifuatazo kutoka kwa swahili hadi kiingereza.kwa mara ya kwanza, chanjo imeonyesha ufanisi mkubwa katika majaribio - kuzuia ugonjwa huo 77 ya wakati kati ya wale wanaoupokea.  <response>: for the first time, a vaccine has shown high effectiveness in clinical trials, stopping the illness in 77 percent of people who received it. 