Highlights
•  Polysaccharides have broad antiviral activity, unique mechanism and good safety.
•  Some marine and Chinese medicine polysaccharides have strong anti-coronavirus activity.
•  Polysaccharide adjuvant can enhance the immunity and antiviral effect of vaccine.
•  Polysaccharides play important roles in antiviral nanomaterial and delivery system.
•  A new idea to develop COVID-19 vaccine combining polysaccharides and nanotechnology is proposed.