COVID-19 vaccines in 2023.

Area of Science:

• Immunology
• Epidemiology
• Vaccinology

Background:

• Most Australian adults possess hybrid immunity against SARS-CoV-2, a combination of vaccination and prior infection.
• Immunity from both vaccination and infection diminishes over time, necessitating ongoing protective strategies.
• Older adults represent the primary demographic at higher risk for severe COVID-19 outcomes.

Purpose of the Study:

• To assess the current state of SARS-CoV-2 immunity in Australian adults.
• To evaluate the effectiveness of different vaccine formulations against circulating variants.
• To inform recommendations on optimal COVID-19 booster timing and vaccine composition.

Main Methods:

• Analysis of population immunity data, considering vaccination history and infection rates.
• Review of clinical data on COVID-19 severity stratified by age and vaccination status.
• Comparison of immune responses and protection offered by monovalent and bivalent COVID-19 vaccines.

Main Results:

• Hybrid immunity is prevalent, but its protective effects decrease over time.
• Bivalent vaccines targeting Omicron subvariants offer improved protection against severe illness compared to original monovalent vaccines.
• Updated monovalent vaccines (XBB.1.5) and bivalent vaccines provide enhanced protection against Omicron variants.

Conclusions:

• Booster doses are essential for maintaining protection, especially in high-risk groups.
• The optimal timing for future booster vaccinations requires further investigation.
• Current COVID-19 vaccines demonstrate a strong safety profile with rare serious adverse events.