Immunity to viral infection requires an immune response to antigens located on the surface of the viral particles or on virus-infected cells. For enveloped viruses, these antigens are often surface glycoproteins. The main limitation of viral vaccines occurs with viruses that show a genetically unstable antigenicity (that is, they display antigenic determinants that continuously vary, such as with influenza viruses or the human immunodeficiency virus [HIV]). Common viral pathogens for which there are vaccines include the following.

A. Hepatitis A

Formalin-inactivated whole virus vaccine produces antibody levels in adults similar to those observed following natural infection and approximately 15 times those achieved by passive injection of immunoglobulin. Projections indicate that immunity to hepatitis A virus will probably last for approximately 10 years after two doses of vaccine. The vaccine is indicated for travelers to endemic areas, men who have sex with men, injecting drug users, and daycare workers. Currently in the United States, hepatitis A virus vaccination is not recommended for children younger than age 2 years because residual anti-hepatitis A passively acquired from the mother may interfere with vaccine immunogenicity.

 B. Hepatitis B

 The current vaccine contains recombinant hepatitis surface antigen. Efficacy is 95 to 99 percent in healthy infants, children, and young adults. Its use is indicated for healthcare workers in contact with blood and persons residing in an area with a high rate of endemic disease. Igs obtained from hyperimmunized humans can provide passive immunity after accidental exposure (for example, from a needlestick or for the neonate of an infected mother). Active and passive treatments can be administered into different sites at the same time. Recommended uses of hepatitis A and B vaccines are shown in Figure 1.

Fig1. Candidates for hepatitis immunization. HBsAg = hepatitis B surface antigen.

C. Varicella zoster

This vaccine contains live, attenuated, temperature-sensitive varicellazoster virus. Its efficacy in preventing chickenpox is approximately 85 to 100 percent in children, and this immunity is persistent. Anti–varicella-zoster Ig provides passive immunity for immunocompromised individuals at risk of infection. A live, attenuated chick enpox vaccine that was approved in 1995 for use in the United States by children age 1 year or older is now recommended as one of the routine childhood vaccines. Mild, breakthrough cases of chick enpox have been reported as a side effect of vaccine administration. The vaccine is also indicated for nonimmune adults at risk of being exposed to contagious individuals. Zostavax is a high-potency version of the chickenpox vaccine, which also contains live, attenuated virus. Zostavax has been approved by the Food and Drug Administration for use in adults over age 50 years for prevention of zoster and, with it, the debilitating effects of postherpetic neuralgia.

 D. Polio

Vaccination is the only effective method of preventing poliomyelitis. Both the inactivated polio vaccine and the live, attenuated, orally administered polio vaccine have established efficacy in preventing poliovirus infection and paralytic poliomyelitis .

1. Inactivated poliovirus (Salk) vaccine: Because the inactivated vac cine cannot cause poliomyelitis, it is safe for use in immunocompromised persons and their contacts. The disadvantages of this inactivated vaccine are: 1) administration is by injection only, and 2) it provides less GI immunity, resulting in the possibility of asymptomatic infection of the GI tract with wild poliovirus, which could be transmitted to other persons. To eliminate the risk for vac cine-associated paralytic poliomyelitis (see next section), an all-inactivated poliovirus vaccine schedule is recommended for routine childhood vaccinations in the United States.

2. Attenuated live poliovirus (Sabin) vaccine: Advantages of this vaccine include: 1) it can be administered orally, 2) it provides lifelong protection from poliovirus for more than 95 percent of recipients after the primary three-dose series, and 3) it provides early GI immunity. The main disadvantage of attenuated live virus vac cine is a small risk of clinical disease, estimated to be 1 per 2.4 million doses.

E. Influenza

The traditional “flu shot” vaccine contains formalin-inactivated virus. A live, attenuated influenza vaccine is administered intranasally. The vaccine provides peak protection about 2 weeks after its administration. Vaccine efficacy of 70 to 90 percent is generally achieved in young adults. The vaccine is recommended for adults older than age 65, high-risk persons age 6 months or older, and those who might transmit the virus to persons at high risk. Antigenic drift requires that individuals be vaccinated against influenza annually prior to the winter flu season.

 F. Measles, mumps, and rubella

 This combination vaccine contains live, attenuated virus and should be administered to young children prior to entering school. Measles vaccine should also be administered to individuals traveling in endemic areas.

J. Human papillomavirus vaccine

 Human papillomavirus (HPV) vaccine is recommended for routine administration in all children beginning at ages 11 to 12 years. Quadrivalent HPV vaccine is the only vaccine approved for males for protection against genital warts, and either quadrivalent or bivalent vaccine may be used in females for the protection against cervical cancer and reducing the incidence of genital warts.

مواضيع ذات صلة

Microbiota, Chronic Infections, and Vaccines

Vaccines and the Role of Pre-existing Immunity

Examples of Protein Subunit Vaccines

Methods for Using Full-Length Antigens (Proteins) as Vaccines

Pan-Genomic Analysis

Reverse Vaccinology

Improving Vaccines over Natural Immune Responses

Selecting Vaccine Antigens

Principles of Vaccine Development

A Brief History of Vaccination

Development of Vaccines for Tuberculosis and Meningitis

Development of Vaccines for Viral Hepatitis, Coronavirus, and Norovirus