Johnson & Johnson said Monday it could have a Covid-19 vaccine available for emergency use early next year and it would begin manufacturing the vaccine immediately.

Though not a major vaccine maker, Johnson & Johnson (ticker: JNJ) was among the first companies to announce a Covid-19 vaccine development program back in January. Now, the company said its program has developed a candidate vaccine and two backup candidates. It plans to begin testing the vaccine in humans in September.

Johnson...