The development of immunization as a means of preventing the spread of infectious disease began in 1796, when Edward Jenner injected cowpox virus, which causes a mild disease, into a child to prevent smallpox, a severe, potentially fatal illness. Immunization today still relies on Jenner’s inoculation methods to protect against disease. There are 2 types of immunization: active and passive.
In active immunization, the recipient develops an acquired immune response to inactivated or killed viruses, viral subtractions, bacterial toxoids or antigens, or synthetic vaccines. Once the immune response to a particular pathogen has developed, it protects the host against infection. The persistence of acquired immunity depends on the perpetuation of cell strains responsive to the target antigenic stimulus; for certain immunogens, booster inoculations may be required.
In general, live, attenuated vaccines produce longer-lasting immunity; however, they are contraindicated in immunocompromised persons or pregnant women because the pathogen can potentially replicate in the host. Ideally, active immunization should be completed before exposure; however, life-saving postexposure immunity can be developed by combining active and passive immunization.
Passive immunization depends on the transfer of immunoglobulin in serum from a host with active immunity to a susceptible host. Passive immunity does not result in active immunity and sometimes even blocks the development of active immunity. Passive immunity is short-lived and does not confer long-term immunity; however, it confers immediate protection on the recipient who has been exposed to the pathogen. Pooled human globulin, antitoxins, and human globulin with high antibody titers for specific diseases are the usual products available for passive immunization.
The current recommended US immunization schedules, developed by the Advisory Committee on Immunization Practices—including immunization schedules for persons aged 0–18 years, the catch-up schedule for individuals aged 4 months to 18 years, and the adult schedule—can be found on the CDC website (www.cdc.gov/vaccines/schedules/index.html). The catch-up protocols are for children who have missed some of the recommended immunization doses.
Immunization should be avoided in persons who have allergic reactions to the vaccine or its components. Idiopathic autoantibody or cross-reacting antibody development may occur after vaccination, resulting in systemic disease such as Guillain-Barré syndrome, a rare but devastating complication of vaccination. Immunization should be avoided during a febrile illness. Multidose immunization schedules that are interrupted can be resumed; however, doses given outside the schedule should not be counted toward completion of the vaccination sequence.
For patients who are pregnant, immunization against tetanus, diphtheria, and influenza is indicated; immunization against other diseases (hepatitis, pneumococcal or meningococcal disease) is indicated if a patient is at high risk of exposure. Additional immunizations may be considered but must be weighed against rare potential risks to the fetus.
The following sections are based on the more extensive recommended immunization schedules in the United States. In other parts of the world, immunizations are performed based on World Health Organization (WHO) guidelines, national programs, or recommendations by multinational organizations such as the European Centre for Disease Prevention and Control (ECDC). As a general rule, national immunization schedules for children are quite similar, but recommended immunizations for adults vary widely between countries (Table 12-2 lists a sampling). For more information on the immunization schedules of EU nations, see the ECDC website (https://vaccine-schedule.ecdc.europa.eu).
Chlibek R, Anca I, André F, et al. Adult vaccination in 11 Central European countries—calendars are not just for children. Vaccine. 2012;30(9):1529–1540.
Robinson CL, Romero JR, Kempe A, Pellegrini C, Szilagyi P. Advisory Committee on Immunization Practices recommended immunization schedule for children and adolescents aged 18 years or younger—United States, 2018. MMWR Morb Mortal Wkly Rep. 2018;67(5):156–157.
US Centers for Disease Control and Prevention. Recommended immunization schedules for adults aged 19 years or older, United States 2019. www.cdc.gov/vaccines/schedules/hcp/adult.html. Updated February 5, 2019. Accessed February 22, 2019.
There are 3 main types of hepatitis viruses. Infection with hepatitis A virus (HAV) is the leading cause of viral hepatitis in the United States. HAV is usually transmitted orally and may be acquired from contaminated water supplies and unwashed or undercooked foods. Vaccination against HAV infection is recommended for children aged 12–23 months and for persons at high risk of exposure to HAV (eg, travelers to endemic areas, patients with blood clotting factor disorders, military personnel, drug abusers, family contacts of infected patients, laboratory workers exposed to the virus). In the United States, 2 preparations are available (Vaqta, Havrix), each consisting of viral antigens purified from human cell cultures.
Approximately 250,000 cases of hepatitis B occur annually in the United States. Between 6% and 10% of adult patients with hepatitis B become carriers, and chronic active hepatitis occurs in 25% of these carriers. Of the patients with chronic active disease, 20% will die of cirrhosis and 5% will die of hepatocellular carcinoma. Worldwide, 250 million persons are chronic carriers.
In the United States, the available recombinant vaccines based on the hepatitis B virus (HBV) surface antigen are Engerix-B and Recombivax HB. In adults, HBV vaccine is usually administered in a series of 3 doses, and 90% of recipients develop protective antibody levels (>10 milli-international units/ml [mIU/mL]), which persist for at least 3 years and may be protective for up to 30 years. Booster injections are advised for persons whose antibody levels are less than 10 mIU/mL. A second vaccination results in the development of protective antibodies in 50% of the initial nonresponders.
Table 12-2 2017 National Adult Immunization Recommendations: A Samplinga
Vaccination before exposure to HBV is recommended and cost-effective for all infants and children and for individuals in certain high-risk groups: health care workers, hemodialysis patients, diabetic adults over age 60, residents and staff of long-term care facilities, household and sexual contacts of chronic carriers of HBV, hemophiliacs, users of illicit injectable drugs, prison inmates, sexually active homosexual men, and HIV-seropositive individuals. Vaccination can be combined with passive immunization for postexposure prophylaxis without affecting the development of active immunity. The incorporation of the vaccine into childhood immunization schedules has resulted in a decrease in the number of new hepatitis B cases reported annually, and there has also been a significant reduction in the number of hepatocellular carcinoma cases reported in children. Some of the available combination vaccines protect against not only hepatitis B, but also hepatitis A, diphtheria, pertussis, tetanus, and polio.
Postexposure prophylaxis with hepatitis B immunoglobulin should be considered when there is perinatal exposure of an infant born to a carrier, accidental percutaneous or permucosal exposure to blood that is positive for the HBV surface antigen, or sexual exposure (within 14 days) to a carrier of HBV. Hepatitis B immunoglobulin should be given as soon as possible after exposure; the recombinant HBV vaccine should be concurrently administered in an accelerated dosing schedule.
Patients with chronic hepatitis B infection and evidence of liver disease may improve after treatment with antiviral medications. If indicated, Interferon or nucleos(t)ide analogues (tenofovir or entecavir) are effective and have a lower incidence of viral resistance than lamivudine.
Hepatitis C is the leading indication for liver transplantation in the United States. The CDC has recommended that all adults in the United States born between 1945 and 1965 have a one-time test for hepatitis C. Early intervention in chronically infected individuals, including treatment and alcohol counseling, can slow the progression of disease. Vaccines against hepatitis C and E are being developed. See Chapter 14 for additional discussion of hepatitis C and other forms of the hepatitis virus.
Smith BD, Morgan RL, Beckett GA, Falck-Ytter Y, Holtzman D, Ward JW. Hepatitis C virus testing of persons born during 1945–1965: recommendations from the Centers for Disease Control and Prevention. Ann Intern Med. 2012;157(11):817–822.
Terrault NA, Bzowej NH, Chang KM, et al; American Association for the Study of Liver Diseases. AASLD guidelines for treatment of chronic hepatitis B. Hepatology. 2016;63(1): 261–283.
Excerpted from BCSC 2020-2021 series: Section 1 - Update on General Medicine. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.