“strongly” recommends adults ages 50 years and older should be offered a COVID-19 vaccine booster shot.Booster shots of an mRNA COVID-19 vaccine “may be offered” to adults ages 18 to 49 at least six months after their second dose, according to NACI.NACI made the recommendations Friday after the Canadian government requested the advisory group to quickly provide the latest directives on booster use as the Omicron variant spreads across the world.“NACI has reviewed the latest data that suggest protection against infection decreases over time since completion of a primary COVID-19 vaccine series,” the group said Friday. “Protection against severe illness remains generally high, but may decrease over time for some people, such as older adults.”.