The world’s leading COVID-19 vaccines may offer lasting protection that diminishes the need for frequent booster shots. That’s according to scientists, who are finding clues in how the body remembers viruses. But they say more research is needed and that virus mutations are still a wild card. Pfizer and Moderna have fueled booster questions by estimating that people might need yearly shots, just like with flu vaccinations. The companies plan to have some candidates ready this fall. But companies won’t decide when boosters get used. That’s up to health authorities in each country. Some experts say boosters may be needed only every few years.