Booster doses are aimed at addressing waning immunity over time. Antibody levels wane for most adults over time, although the level of antibody needed to protect against infection is a lot higher than needed to protect against severe disease if infected. This means that protection against any infection, especially infection with minimal or no symptoms, wanes relatively quickly (within a few months), but protection against severe disease lasts longer, even against delta and omicron variants. Booster doses can assist to build protection backup.
Boosters are now available for all those over 18 years who finished their primary course at least 3 months ago, and for 16-17-year-olds who finished their primary course at least 6 months ago.
Booster doses are particularly important for:
- highly vulnerable people such as the frail elderly or those with significant comorbidities.
- people with continued occupational exposure to SARS-CoV-2 and/or caring for people with COVID-19 disease, such as health care and border workers. They are more likely to be exposed to SARS-CoV-2 infection and have a higher potential to transmit the infection to people at risk of severe disease.
- those living in households with people with immunocompromise.
Booster doses for immunocompromised
A booster dose for immunocompromised can be given anytime from 3 months (ideally 6 months) after they have had their third primary dose.