Despite the extensively vaccinated population, cases and reinfections of SARS-CoV-2 are continuously rising worldwide. The frequent occurrence of new, highly transmissible variants substantially weakens protection against infection over time.

At the start of this year, many vaccine manufacturers have begun the clinical trial of Omicron-based boosters. Although these boosters show good performance against other strains, there is an increasing amount of uncertainty on the length of effectiveness due to the significant decrease in the most contagious version, BA.5. FDA has recommended that vaccine manufacturers focus on developing a bivalent vaccine containing BA.4/5 components.