Answer:

After global approval of one or more Covid-19 vaccines, Covid-19 has become the 28th vaccine  preventable  human  disease  (https://www.who.int/teams/immunization-vaccines-and-biologicals/strategies/global-vaccine-action-plan).  Not  all  infectious  diseases  can  be  presently fought with a vaccine. The HIV, respiratory syncytial virus, and the cancer-causing Epstein-Barr virus kill  millions of  people every year  and have no  vaccine  yet. Moreover,  not everyone  is fortunate enough  to be  vaccinated  due to  several economic, social,  ethical, geographical and health reasons leading to vaccine preventable deaths. The health reasons for avoiding vaccines include 1) historical evidences of severe or life-threatening reaction to the vaccine (allergies), 2) infants younger than 6 months old (for many vaccines), 3) ongoing moderate or severe illness and  4)  people  with  chronic  wasting  diseases  or  those  with  Guillain-Barre  syndrome (characterized by difficulties with eye muscles and vision, swallowing, speaking, chewing, lack of sensations in the hands and feet but severe pain especially at night, problems of coordination and steadiness beside arrhythmic heart beat and disturbed blood pressure). The most common flu shots are not suggested be administered to children under 2 years of age, or young children with a history of asthma or wheezing, children or adolescents on long-term aspirin treatment and pregnant women. Also, people with chronic diseases, (such as heart disease, liver disease, or asthma), people with certain muscle or nerve diseases (that can cause breathing problems) and  people who  have (or  are living  with family  members) compromised immune systems should not go for flu vaccine.