WASHINGTON (AP) — Federal health regulators have again extended the expiration dates on Johnson & Johnson’s COVID-19 vaccine by another six weeks. The Food and Drug Administration said in a letter to J&J on Wednesday that the shots remain safe and effective for at least six months when properly refrigerated. The agency previously authorized the vaccine’s shelf life for up to 4 1/2 months. The change gives health workers across the U.S. more time to use remaining shots sitting at pharmacies, hospitals and clinics. After plateauing earlier this summer, U.S. vaccination rates have begun climbing again as the contagious delta variant surges across many parts of the country.