All authorised COVID-19 vaccines have high levels of vaccine effectiveness against hospitalisation, severe disease and death against both the Alpha and the Delta variants. While there is some decline in protection against infection with time from primary vaccination, high protection against severe disease is retained for at least six months.
Declines in vaccine effectiveness with an increase in breakthrough infections in those aged 65 and older, increasing with age, have been reported from Israel and the US. This decline may be due to waning immunity in older persons coupled with relaxation of non-pharmaceutical interventions and the emergence of the Delta variant.