Immunity and Immunizations

Disease control and prevention are central to an effective program of infection control. It is always better to prevent a disease than to be required to treat that disease.

A person's first line of defense against foreign organisms involves the barrier tissues (eg, intact skin or mucous membranes) and certain other secretions (eg, sweat, tears, mucous, stomach secretion, and saliva). Secretions can mechanically wash away microorganisms or prevent their attachment to body surfaces. Secretions also contain nonspecific antimicrobial factors, and the pH of certain fluids can adversely affect the viability of microorganisms. This type of response involves the innate or nonspecific immune system. Defense is directed against all types of foreign microorganisms and is not specifically directed against any particular pathogen.1 Furthermore, processes such as fever, sneezing, coughing, and vomiting can also be considered to be protective.

The other critical means of protecting an individual from infection is the specific or adaptive immune system. The biological events include identification of the foreign invader (eg, specific antigens) followed by a specific response to those antigens. Specific immunity has 2 interacting components: (1) humoral immunity, which involves the generation of different classes of antibody; and (2) the cell-mediated response through which biologically active cells specifically recognize and destroy potential pathogens.1,2

Immunity is the ability of the human body to tolerate the presence of indigenous cells and tissues ("self") and to neutralize or eliminate foreign microorganisms ("nonself"). Infectious agents such as bacteria, fungi, and viruses are identified as being foreign by the immune system.

There are 2 basic ways immunity can be acquired—actively and passively.

Active immunity is protection produced by a person's immune system when directly challenged by the antigen. This type of immunity is usually long lasting or permanent.

Passive immunity is protection that results from antibodies produced by an animal or another human and transferred to a recipient, usually by injection. Immunity can thus be acquired without the immune system being challenged by an antigen. Passive immunity provides effective protection, but the effect can fade within a few weeks or months.1


Naturally acquired active immunity refers to the natural exposure to an infectious agent or antigen(s). The body responds by producing antibodies (humoral immunity) and biologically active cells (cellular immunity). Exposure to different pathogens leads to subclinical or clinical infections, which hopefully results in the development of protective immune responses.1,3

Naturally acquired passive immunity is a process through which an individual develops immunity by receiving antibodies from another person through natural processes, such as nursing or placental transfer. Two classes of antibodies (immunoglobulin IgA and IgG) are found in human colstrum/milk. The placental transfer of IgG from mother to fetus occurs during pregnancy. The protection offered by these antibodies generally lasts 4 to 6 months after birth. Maternal antibodies help protect infants until their immune systems are more fully developed.1,3

Artificially acquired active immunity is achieved by administering live or dead pathogens or their components. Vaccines used for active immunization consist of viable (attenuated) microorganisms, killed whole or split organisms, microbial components, or inactivated toxins (toxoids).3

Artificially acquired passive immunity is accomplished by injection with gamma globulin (antibodies) from other humans or another species which is immune. Gamma globulin is often used to treat acute infections and poisonings and as a prophylactic measure. Immediate protection occurs. However, protection is effective for only a short duration (ie, the time the introduced antibodies remain in circulation). Furthermore, injection of foreign antibodies can illicit an adverse response in the recipient.

Passive transfer of cell-mediated immunity is also possible for some disorders (eg, cancer and immunodeficiencies) but is by no means routine. Finding a histocompatible donor is difficult, and there is also a significant risk of graft-versus-host disease.1,3


There are 3 basic types of vaccines: (1) live or attenuated, (2) inactivated or killed, and (3) recombinant.

Live organisms are used to immunize against a number of viral (eg, smallpox, mumps, measles, chickenpox, rubella, oral poliovirus vaccine, and influenza) and bacterial (eg, oral typhoid vaccine) infections. Disease-producing (or "wild-type") viruses and bacteria are modified (attenuated, or made less pathogenic) in a laboratory to produce the live vaccine. The resulting vaccine organisms retain their ability to replicate and produce an immune response in the person being vaccinated. Replication is needed for the vaccine to be effective. The immune response is thus similar to that following a natural infection. Normally, self-limiting, nonclinical infections develop. Usually, live vaccines are effective with the application of a single dosage.1,3

There are risks associated with live vaccines. They can reproduce and cause severe or even fatal disease when administered to an immuno-compromised individual. Attenuated organisms could also revert back to their original pathogenic form.1 Active immunity from a live vaccine may not develop because of interference from circulating antibodies to antigens presented by the vaccine. Antibodies from other sources such as a transplantation or transfusion can cause vaccine failure. Prior to actual vaccination, live vaccines can be damaged or destroyed by heat or sunlight.

Inactivated vaccines consist of whole particles and cells killed by heat, chemicals (usually formalin), or ultraviolet light. There are a number of killed viral and bacterial vaccines available. Fractional or subunit vaccines are prepared by the further processing of killed organisms. Purification can produce high concentrations of a specific protein and/or polysaccharide. Inactivated vaccines do not contain viable microorganisms and thus cannot replicate, even in immuno-deficient persons.1,3

Whole-particle viral vaccines include influenza, inactivated poliovirus vaccine, rabies, and hepatitis A. Fractional (subunit) vaccines are available for hepatitis B, influenza, acellular pertussis, and typhoid, and in a toxoid form for diphtheria and tetanus.1

Inactivated vaccine antigens usually are not affected by circulating antibodies. Inactivated vaccines generally (1) are not as effective as live vaccines, (2) require 3 to 5 doses, and (3) primarily produce a humoral immune response. The resulting antibody level (or titer) tends to fall off over time and may require booster injections.1,3

Vaccine antigens can also be produced by genetic engineering (recombinant) technology. Two such vaccines are available to prevent hepatitis B.1-3


There is evidence that healthcare workers are occupationally at risk for a variety of infections. Unfortunately, vaccines do not exist for 2 very important bloodborne pathogens: hepatitis C and HIV (human immunodeficiency virus). However, vaccines are available for hepatitis B, influenza, measles, mumps, rubella, and varicella.4-6

While not all vaccine-preventable diseases are overt occupational hazards for dental personnel, a review of the immune status of all dental healthcare workers (DHCWs) against measles, mumps, rubella, and varicella would be prudent. In recent years, there have been reports of these diseases occurring among unvaccinated personnel. Primary health providers and medical histories may have to be consulted to determine if a DHCW had been previously infected.

There are 2 diseases for which DHCWs are clearly at occupational risk. These are hepatitis B (HBV) and influenza, but vaccines are available to prevent both infections.


HBV infection is the major occupational disease hazard for all healthcare workers, including DHCWs. The risk of contracting HBV depends on how frequently DHCWs contact blood and blood products through percutaneous or permucosal exposure. Any person who could be exposed to blood/blood products should be vaccinated against HBV7 because 10% of people infected with HBV become chronic carriers.

Before 1982, an estimated 150,000 to 450,000 persons in the United States were infected with HBV each year. This included approximately 20,000 children. If children under the age of 5 years are infected, the chances of them developing chronic infections are unusually high (30% to 90% versus 2% to 10%).7-9

The first HBV vaccine was licensed in United States in 1981 and became readily available in 1982. It was derived from the plasma of infected humans. In 1986, the first vaccine ever produced by recombinant DNA technology was released. Within 4 years, there were 2 recombinant HBV vaccines. OSHA mandated HBV vaccination for at-risk HCW as part of its Bloodborne Pathogens Standard issued in 1991.7-10

Both vaccines use hepatitis B surface antigen (HBsAg) synthesized by genetically engineered Saccharomyces cerevisiae (common baker's yeast). The vaccine contains only the HBsAg protein. No live virus is present. Usually, vaccination requires 3 injections. The first 2 are given 4 weeks apart. The final injection is administered 4 to 6 months after the first. The vaccines are considered to be interchangeable; therefore, the vaccination series can be started with one brand and completed with the other.7,8

If properly administered, the HBV vaccines are considered to be 90% to 95% effective in preventing HBV infection and clinical hepatitis among healthy children and young adults. However, among immuno-suppressed persons, those with chronic health problems, men, overweight persons, and smokers, the percent of people who seroconvert can be considerably lower. Some individuals appear to be genetically predisposed to an inadequate response. Successful vaccination prevents HBV disease and the serious symptoms associated with chronic infection, including cirrhosis and hepatocellular carcinoma. Thus, the HBV vaccines are considered to be the first immunization against cancer. 7-10

Recently, a meta-analysis of more than 20 studies indicated a possible correlation/ link between recipient age and successful immunization.11 It is known that the immune response diminishes as a person ages. The study noted suboptimal immune responses among persons as young as 30 years of age. The 2 types of HBV vaccines were approximately equally effective among older recipients. These results are important because it indicates that some younger people may not be adequately protected after vaccination. Also, persons of childbearing age could be affected.

At this time, there is no recommendation regarding booster injections. Current data indicate that when vaccination is successful, protection can last at least 15 years. However, the only way to truly determine protection is through serological screening for the antibody titer. Ideally, this should be checked within several months of completing the vaccination series. Unfortunately, screening does not generally occur. If the antibody titer test indicates an inadequate response, then a second vaccination series should be administered. An absence of an antibody titer after vaccination could also indicate the presence of chronic HBV infection. Nonresponders should be tested for HBsAg, which would indicate preexisting infection. After completion of a second series, recipients should be tested for both HBsAg and antibody titer to HBsAg. It is important to emphasize that HBV is a serious disease. A lack of an immunologic response following immunization should involve a consultation with a gastroenterologist.

Because of greater vaccination coverage, improved infection control and prevention, and changes in the behavior of at-risk populations in response to HIV/AIDS, the number of persons infected with HBV in 2001 declined to 79,000.7-10 During the period from 1982 to 2002, an estimated 40 million infants and children and 30 million adults have received the HBV vaccine series.7

In 1982, the levels of HBV infection among dentists and dental hygienists were high; 15% had serologic markers of a current or recent infection. Prevalence rates among oral surgeons was at least twice that high.10

If DHCWs acquire HBV infections, there is a possibility that infected practitioners could pass the infection on to their patients. In fact, there have been 10 documented cases of dentists infecting their patients. The last occurred in 1984, involved 26 patients, and resulted in 2 fulminant (fatal) cases.10


Influenza is spread from person to person through mists or sprays of infectious respiratory secretions as a result of coughing and sneezing. Influenza affects all age groups and causes moderate to severe illness, loss of time from school and work, and complications such as pneumonia. The "flu season" in the United States runs from November through April each year.12,13 Epidemics can affect 10% to 20% of the population and are associated with an average of 36,000 deaths and 114,000 hospitalizations each year in the United States. Over 90% of these deaths occur in persons 65 years or older.12,13

A yearly vaccination against influenza is recommended for the following groups considered to be at increased risk for serious complications12,13: (1) persons ≥ 50 years of age; (2) residents of nursing homes and other long-term care facilities that house persons of any age who have long-term illnesses; (3) anyone ≥ 6 months of age who has chronic heart or lung conditions, including asthma; (4) adults and children ≥ 6 months of age who need regular medical care or have been hospitalized because of metabolic diseases (eg, diabetes), chronic kidney disease, or a weakened immune system (eg, HIV/AIDS or immuno-suppressive medication); (5) children and teenagers aged 6 months to 18 years who are on long-term aspirin therapy and therefore could develop Reyes Syndrome after the flu; and (6) women who will be more than 3 months pregnant during the flu season.

A person with the flu can readily transmit the infection to others. The following persons should also be vaccinated: (1) healthcare workers, including members of the dental profession; (2) employees of nursing homes and other types of long-term care facilities who have contact with patients or residents; (3) employees of assisted living and other residences for people in high-risk groups; (4) people who provide home care to those in high-risk groups; and (5) household members (including children) of people in high-risk groups.

The ideal time to receive vaccination against influenza is in October or November. People to be vaccinated should first include those at highest risk and healthcare workers.12,13

Injectable influenza vaccines in the United States are prepared from inactivated virus, which is then disrupted. The vaccine does not contain any viable virus and thus is incapable of causing an infection. The composition of the trivalent 2003-2004 influenza vaccine in the United States is A/New Caledonia/20/99-like (H1N1), A/Moscow/10/99-like (H3N2), and B/Hong Kong/330/01-like viruses.12

Vaccination of adults requires one intramuscular injection. Children under 9 years of age require 2 injections. The vaccine is inexpensive, well tolerated, and has an overall protection rate of 70% to 80%. Fortunately, the risk that the vaccine will cause serious harm is extremely small. Problems are usually mild (eg, soreness, redness or swelling at the injection site, fever, or body aches), and these last only 1 to 2 days. A discussion with a physician is required of those with allergies to eggs, a previous vaccination, or a history of Guillain-Barr—Syndrome.12,13

On June 17, 2003, the FDA approved an intranasal, trivalent, cold-adapted, live, attenuated influenza vaccine called FluMist.13 It is designed to immunize healthy persons 5 to 49 years of age in order to prevent influenza A and B. Persons 9 years and older require a single dose, while children between 5 and 8 years of age require 2 doses given 6 weeks apart. However, on September 25, 2003, the Centers for Disease Control and Prevention released an important statement concerning the use of live, attenuated influenza vaccines.13 It stated that no data are available assessing the risk for transmission of LAIV (live attenuated influenza vaccine) from vaccine recipients to immuno-suppressed contacts. In the absence of such data, use of inactivated influenza vaccine is preferred for vaccinating household members, healthcare workers, and others who have close contact with immuno-suppressed persons because of the theoretical risk that a live, attenuated vaccine virus could be transmitted to the immuno-suppressed person and cause disease. Otherwise, no preference is given to either inactivated influenza vaccine or LAIV for vaccination of healthy persons aged 5 to 49 years in close contact with all other groups at high risk.

Until data exist that better describe the risks and benefits associated with immunization by nasal spraying, healthcare workers should be immunized by injection of inactivated influenza vaccine.


1. Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases, 7th ed., Atlanta, GA: Centers for Disease Control and Prevention; 2003,1-266.

2. Centers for Disease Control and Prevention. National Immunization Program. Available at: Accessed: December 2003.

3. Ghaffar A. Online Microbiology and Immunology Textbook — Immunization. Available at: Accessed: December 2003.

4. Centers for Disease Control and Prevention. Immunization of health-care workers — recommendations of the Advisory Committee on Immunization Practices (ACIP) and the Hospital Infection Control Practices Advisory Committee (HICPAC). MMWR. 46 (RR-18):1-42, 1997.

5. Association for Professionals in Infection Control and Epidemiology. Guideline for infection control in health care personnel, Am J Infect Control. 26:289-354, 1998..

6. Palenik CJ and Govoni M. An immunization program for dental practices. Compendium. In Press.

7. Centers for Disease Control and Prevention. Hepatitis B vaccination — United States, 1982-2002. MMWR. 51:549-552, 2002.

8. US Department of Labor, Occupational Safety and Health Administration. 29 CFR Part 1910.1030 Occupational exposure to bloodborne pathogens; Needlestick and other sharps injuries, Final rule, Federal Register 66 (12):5317-5325, 2001. As amended from and including Federal Register 1991 29 CFR Part 1910.1030. Occupational exposure to bloodborne pathogens, Final rule. 56 (235): 64174-64182, 1991. Available at: / Accessed: December 2003.

9. Centers for disease Control and Prevention. Viral hepatitis B. Available at: Accessed: December 2003.

10. Cottone JA and Puttaiah M. Viral hepatitis and hepatitis vaccine. In: Cottone JA, Terezhalmy GT and Molinari JA. Practical Infection Control in Dentistry, 2nd edition. 1996, Williams & Wilkins, Baltimore, MD, pp. 15-47.

11. Fisman DN, Agrawal D, Leder K. The effect of age on immunologic response to recombinant hepatitis B vaccine: a meta analysis. Clin Infect Dis 35:1368-1375, 2002.

12. Centers for Disease Control and Prevention. Update: influenza activity — United States and worldwide, 2002-2003 season and composition of the 2003-2004 influenza vaccine. MMWR. 52:516-221, 2003.

13. Centers for Disease Control and Prevention. Using Live, Attenuated influenza vaccine for prevention and control of influenza. MMWR 52(RR-13):1-8, 2003.

Dr. Palenik has held over the last 25 years a number of academic and administrative positions at Indiana University School of Dentistry. These include Professor of Oral Microbiology, Director/Human Health & Safety, Director/Central Sterilization Services and Chairman/Infection Control and Hazardous Materials Management Committees. Currently he is Director/Infection Control Research & Services. Dr. Palenik has published 125 articles, over 290 monographs, three books and seven book chapters, the majority of which involve infection control and human safety and health. Also, he has provided over 100 continuing education courses throughout the United States and eight foreign countries. All questions to be directed to OSAP by e-mail at This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Ms. Govoni is a certified and registered dental assistant and a registered dental hygienist with over 31 years of experience in the dental profession as a chairside assistant, office administrator, clinical hygienist, educator, consultant, and speaker. She is the owner of Clinical Dynamics, a consulting company dedicated to the enhancement of the clinical and communication skills of dental teams. She is a past president of the American Dental Assistants Association, a member of the Organization for Safety and Asepsis Procedures, the American Dental Hygienists Association, the National Speakers Association, and served on the Michigan Board of Dentistry. She is also a columnist for Dental Equipment and Materials, and is a featured speaker on the ADA Seminar Series.

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