**4. Conclusion**

Influenza virus infection is a continuing health and economic burden that causes epidemics with pandemic potential, impacting 5–30% of the world population each year and resulting in millions of hospitalizations and thousands of fatalities. Because of its great vulnerability to antigenic variation, influenza A is the type most responsible for pandemics. Influenza is extremely infectious, with symptoms including fever, cough, chills or sweats, myalgias, and malaise. The hypervariability of the amino acid sequences encoding HA and NA is primarily responsible for epidemic and pandemic influenza epidemics, which are the result of antigenic drift or shift. As a result, research on an effective broadly-reactive influenza vaccine capable of providing protection against both seasonal and pandemic influenza is now underway.
