On 4 June, in what's called an update, the Singapore Ministry of Health—and a number of jurisdictions referred to Singapore; in fact, initially Australia did—referred to the work; there's a working group out of Singapore that's exploring this. The Singapore Ministry of Health said this: "Local data to date shows protection against severe disease as sustained after the third mRNA booster. However, there can be waning of protection, particularly in the elderly and medically vulnerable. International studies show that vaccine efficiency against hospitalisation declines after the third dose mRNA booster. Persons aged 80 years and above, residents of aged care facilities, and medically vulnerable persons are at increased risk of severe disease and will be most affected by waning vaccine efficiency over time. These persons are therefore recommended to receive a second booster dose—that is, a fourth dose of receiving an mRNA vaccine—from about five months after receiving their first booster dose for personal protection against severe disease."