LONDON (AP) — Johnson & Johnson says a booster dose to its one-shot coronavirus vaccine provides a strong immune response months after people receive a first dose. The company said Tuesday an extra dose — given two months or six months after the initial shot — revved up protection. The results haven’t yet been published or vetted by other scientists. The J&J vaccine was considered an important tool in fighting the pandemic because it requires only one shot. But even as rollout began, the company already was running a global test of whether a two-dose course might be more effective.