First of all, there is some evidence from offshore that a fourth dose—a second booster—may be beneficial to those most vulnerable to COVID. This includes particularly the immunocompromised and older people. On 19 May—that's three weeks ago—the US Centers for Disease Control and Prevention (CDC) made a recommendation in their document titled CDC Strengthens Recommendations and Expands Eligibility for COVID-19 Booster Shots. In this CDC document, they say: "In addition, today CDC is strengthening its recommendation that those 12 and older who are immunocompromised and those 50 and older should receive a second booster dose at least four months after their first." This is CDC three weeks ago.