Epidemiology and Control: From Principles to Pandemics

Abstract

Viral disease is a product of the interaction between the agent, the host, and their environment. Each virus may have its own intrinsic infectivity, virulence, and pathogenicity. Beyond age, sex, and race, various other host biological and behavioral attributes affect acquisition of viral infection and/or its course and manifestations. Physical, chemical, and biological factors in the environment operate on the virus itself and may also alter the host biological or behavioral response. Viral infections have incubation periods usually lasting days or weeks before their acute expression, while viruses that establish latency may produce pathologic sequelae years or decades after infection occurs. The degree or intensity of host response and clinical expression is likewise highly variable, ranging from largely inapparent to highly lethal. The virus-specific degree of cell, tissue, and organ damage is also variable. Common clinical syndromes involve the respiratory, gastrointestinal, blood, and lymphoid, and central nervous systems; the liver; and mucocutaneous surfaces. Viruses spread horizontally by multiple modes, using one or more bodily surface or fluid as a route of exit or entry, either by direct or indirect contact. Vertical transmission may produce a variety of congenital and perinatal conditions. Different viral infections may be present nearly ubiquitously or propagate continuously throughout a population (endemic); or they may occur only sporadically, in seasonal rhythm, or in unexpectedly explosive form (epidemic). Although many viruses are refractory to all known therapeutic agents, for some, the increasing numbers of highly effective agents that act directly on the viral synthesis or enhance host response mechanisms hold great promise. Vaccines have produced numerous historical successes at viral disease control domestically and globally; they are essential to progress toward elimination and eradication. Many viral infections, however, remain refractory to vaccine development, and distrust of vaccine safety or efficacy has become inimical to the reduction of vaccine-preventable infections. Nevertheless, remarkable scientific advances and major government and private sector initiatives for treatment and prevention have raised expectations of successful control for HIV/AIDS, hepatitis C, human papilloma virus, and other widespread and previously intractable viral diseases. The twenty-first century has been marked by the repeated emergence of novel viruses with pandemic potential. The COVID-19 pandemic has illustrated the challenges of detecting and controlling these infections, the dire consequences of logistic and communication failures by local and national leaders, the need for investment in preparedness, and yet the almost inconceivably rapid triumph of initial vaccine development by amply resourced scientific, public health, and commercial enterprises.

The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention.