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.
1. How effective is the 2018 flu shot? Early findings from Canada indicate a 17 percent effectiveness against the viral strain, known as H3N2, thatâs been the main culprit of flu in the U.S. this winter. 2. Why are vaccines less protective against some strains of the flu? One reason has to do with the most-common way flu shots are made.