Causes of a temporary rapid pulse include anxiety, fever, stress and exercise. Tachycardia causes a prolonged, sustained elevated heart rate, and it may cause your heart rate to increase to 400 beats per minute, notes the Heart Rhythm Society.
New flu vaccines are released every year to keep up with rapidly adapting flu viruses. Because flu viruses evolve so quickly, last year's vaccine may not protect you from this year's viruses. After vaccination, your immune system produces antibodies that will protect you from the vaccine viruses.
This vaccine is used to prevent infection by the influenza (flu) virus. It is also called the seasonal flu shot. Influenza can cause serious illness (rarely death), especially in people at high risk from the infection (such as young children, the elderly, and people with chronic health problems). Vaccines work by causing the body to produce its own protection (antibodies) against the virus.