Introduction

Since the dawn of humanity, infectious diseases have been an enormous challenge to the survival of the species. It was only in the mid-20th century that we began to be able to control them in adults and children but still unsatisfactorily in the elderly. By age 60, people become more susceptible to infections, particularly emerging ones. Furthermore, when affected by an infection, they suffer more severe outcomes than younger people. A great example is mortality from influenza in the United States, where about 30,000 people die each year, being over 95% elderly (REID; TAUBENBERGER, 2003).

Since the invention of the vaccine, we have witnessed a radical change in the quality and potential of human life. Many factors have allowed this progress beyond vaccination, such as decreasing child mortality, antibiotic therapy, preventing heart and metabolic diseases, improving nutritional and hygiene conditions. The greatest evidence of this is the constant increase in average life expectancy in the world. Recent studies indicate that such growth will allow many children born in the 2000s to live to 100 years in developed countries (MANTON; VAUPEL, 1995).

This increase in life expectancy is reflected in the elderly population, which is currently the fastest-growing. According to the United Nations, in 2015 there were around 901 million elderly people, of which about 125 million were over 80 years old (UN, 2016). In addition, this population will constitute 25% of the world's population in 2030 and will double in 2050 to 2.1 billion, of which 434 million will be over 80 years old (UN, 2016).