Table 1.

Preparation, advantages, and disadvantages of existing vaccines.

Existing Vaccine	Preparation	Advantages	Disadvantages	References
Attenuated vaccines	Produced from pathogenic isolates via serial passage in embryonated, specific, pathogen-free eggs	Cause a strong immune response; long-lasting immune response; can survive the low-pH enzymatic environment of the stomach	Risk of toxic recovery in immunocompromised individuals; low safety profile	[3,4]
Inactivated vaccines	Formaldehyde inactivates live virus production	Compared with live attenuated vaccines, the safety is improved, and the production process is mature	Weak immune response; short duration; destruction or alteration of antigens; high cost; multiple vaccinations required	[4]
Subunit vaccines	Antigenic proteins from pathogens	High safety; modulated immune response; clear target antigen	Low immunogenicity	[4,5,6,7]
DNA vaccines	Transfection of DNA encoding a certain antigenic protein into animal cells	Simple to build; easy to mass-produce; high security and high stability	Cannot be used in humans; naked-pelleted DNA has low immunogenicity	[8,9,10,11]
mRNA vaccines	Transfection of RNA encoding a certain antigenic protein into animal cells	High transfection rate and simple process	Unstable; lack of effective delivery vehicles in vivo	[8,14,15,16,17,18,19]