3.5 Immunization
Immunization provides protection against specific infectious diseases and is one of the greatest achievements of medical science and public health. It is the right of every child to be protected against vaccine-preventable diseases: parents, caregivers and health professionals need to ensure that immunization is available to all children.
Protection against subsequent infection after surviving the initial challenge has been recognized for many centuries for some infections. The use of material from smallpox lesions for vaccination was practised in early dynasties in China. Edward Jenner recognized that vaccination with cowpox virus could protect against challenge with smallpox. Smallpox was declared eradicated worldwide in 1979.
Diphtheria immunization began in the 1920s, and immunization campaigns against pertussis (whooping cough) were initiated in the 1940s. In the 1950s, triple antigen vaccine (DTP: diphtheria, tetanus and pertussis) was introduced and polio immunization campaigns began, leading to its elimination in the developed world. It is likely that poliomyelitis will be the second vaccine-preventable disease to be eradicated worldwide. Measles immunization has been available for more than 40 years, and the last decade has seen the introduction of many new vaccines with rapid impact on rates of serious infections such as meningococcal and pneumococcal disease.
Immunization remains one of the most important public health priorities in developed and developing countries. In the developing world, many millions of childhood deaths occur each year from vaccine-preventable diseases such as tetanus, pneumonia, diarrhoea and measles because of lack of access to vaccines and vaccine provider services. Thus, immunization and its promotion remains one of the major activities of the World Health Organization, with the aim of achieving universal immunization for children.
Principles of immunization
Immunization may be passive or active.
Passive immunity
Passive immunity refers to the acquisition of preformed antibody. The fetus receives maternal immunoglobulin (Ig) G antibodies during the later weeks of pregnancy, and breastfeeding supplies IgA antibody at the mucosal surfaces of the gastrointestinal tract.
Passive immunization as a means of disease prevention is used in the form of:
• normal human immunoglobulin for protection against measles and hepatitis A, and in children with immunodeficiency
• specific high-titre preparations against cytomegalovirus (CMV), varicella, tetanus, rabies, hepatitis B and diphtheria (for use as post-exposure prophylaxis in high-risk situations or in immunocompromised children), and as
• humanized monoclonal antibody against respiratory syncytial virus (RSV) infection (may be used as primary prophylaxis in children with chronic cardiac and lung disease).
Passively acquired immunoglobulin has a relatively short half-life and does not lead to active immunity or long-term protection.
Active immunization
Active immunization involves administering a vaccine antigen so that a protective immune response develops that is similar to that occurring after naturally acquired infection. This immune response should be one that entails the development of persistent immunological memory, and long-term protection from the infectious disease.
Active immunization to prevent infection or the effects of infection may be performed using:
Requirements of vaccines
Principles of vaccine selection
Common infectious diseases and the vaccine types used for prevention of these diseases are listed in Table 3.5.1. The immunization strategies used for these diseases have been developed to take account of the following factors:
• The nature of the disease process. For example, toxoid vaccines are used to prevent diseases in which exotoxins are responsible for the disease such as diphtheria and tetanus.
• The route of infection. For example, oral rotavirus vaccines have been developed to provide protective mucosal immune responses to rotaviruses, which are a major cause of severe gastrointestinal tract infections in infants.
• Variability of the organisms causing disease. For example, influenza vaccines need annual modification to provide protection from prevalent circulating strains; polio vaccines (oral and inactivated) contain the three strains of the poliovirus that cause disease, and pneumococcal vaccines contains polysaccharide from 7 to 23 of the most common strains that cause disease out of more than 90 strains of pneumococci.
• The nature of the immune response at different ages. For example, Haemophilus influenzae type b (Hib) vaccines, meningococcal C vaccine and pneumococcal vaccines are much more effective in infants when given as polysaccharide–protein conjugate vaccines rather than purified polysaccharide vaccines because of the poor immune response to polysaccharides at this age.
• The effects of maternal antibodies on vaccine responses in infants. Measles immunization is not undertaken until the age of 9–12 months in most countries because passively acquired maternal antibody remains in sufficiently high concentration to neutralize the administered live attenuated vaccine virus strain in the infant prior to this age.
• The age at which children are most susceptible to infection. Meningococcal C conjugate vaccines are given as a single dose at 12 months of age in Australia as meningococcal C disease was rare before that age, whereas in the UK it is given to infants at 2, 4 and 12 months of age as the peak incidence was between 6 and 12 months of age.
• The ability to reduce transmission in the community and induce herd immunity. For example, rubella immunization is given to all children to provide longlasting immunity for girls before their childbearing years, and to decrease the circulation of rubella in the community, and therefore the risk of exposure of pregnant women to rubella. These strategies have resulted in a dramatic decrease in fetal rubella infection and the associated malformations that occur in early pregnancy (congenital rubella embryopathy).
• The ability to optimize immunization coverage for the high-risk population. A targeted strategy of hepatitis B vaccination in newborns of mothers who are hepatitis B carriers to prevent perinatal transmission was ineffective in immunizing the at-risk infants so universal newborn hepatitis B immunization has been implemented in Australia.
Table 3.5.1 Vaccine types for schedule vaccines and other commonly available vaccines
| Disease | Vaccine type |
|---|---|
| Schedule vaccines | |
| Hepatitis B | Recombinant subunit vaccine |
| Diphtheria | Toxoid (formaldehyde-treated toxin) |
| Tetanus | Toxoid (formaldehyde-treated toxin) |
| Pertussis | Acellular vaccine containing 2–5 protein antigens from Bordetella pertussis |
| Haemophilus influenzae type b (Hib) | Polysaccharide protein conjugates (PRP-OMP, PRP-T) |
| Poliomyelitis | IPV: inactivated poliovirus vaccine (types 1, 2 and 3) |
| Measles, mumps and rubella | Attenuated live viruses (freeze-dried) |
| Varicella | Attenuated live virus (freeze-dried) |
| Pneumococcal infections | Conjugate vaccine containing 7, 10 or 13 pneumococcal serotypes |
| Meningococcal C disease | Meningococcal C conjugate vaccine |
| Other commonly used vaccines | |
| Influenza | Subunit vaccine derived from inactivated virus |
| Hepatitis A | Inactivated hepatitis A strain |
| BCG | Live attenuated bacteria |
| Pneumococcal infections | Polysaccharide vaccine containing 23 pneumococcal serotypes (not conjugated) |
| Meningococcal infections | Quadrivalent vaccine containing A, C, W135 and Y polysaccharides (both conjugated and unconjugated available) |
BCG, bacille Calmette–Guérin.
Immunization schedule for routine childhood immunization
The national immunization schedule in countries is generally recommended by an expert committee and is then funded by the government at a later stage. The current Australian schedule is presented in Table 3.5.2. There are differences in the schedule in individual countries and sometimes within countries because of variations in the epidemiology of some diseases, the registration and prices for supply of different types of vaccine, and national priorities and public demand. The immunization schedule has changed significantly in recent years with the availability of new vaccines and is likely to change frequently in the future, so it is important to keep up to date.
Table 3.5.2 National Health and Medical Research Council National Immunization Programme for Australian children
| Age | Vaccine | Route |
|---|---|---|
| Birth | HBV | IM |
| 2, 4 and 6 months | DTPa* | IM |
| Hib* | IM | |
| IPV* | IM | |
| HBV* | IM | |
| PCV | IM | |
| RV | Oral | |
| 12 months | MMR | SC |
| Hib† | IM | |
| MenCC† | IM | |
| 18 months | Varicella | SC |
| 4 years | DTPa-IPV | IM |
| OPV | Oral | |
| MMR | SC | |
| 12–15 years | dTpa | IM |
| Varicella‡ | SC | |
| HBV§ | IM | |
| HPV¶ | IM |
HBV, recombinant hepatitis B vaccine; DTPa, infant formulation of acellular diphtheria, tetanus and pertussis vaccine; Hib, Haemophilus influenzae type b conjugate vaccine; IPV, inactivated poliovirus vaccine; OPV, oral poliovirus vaccine; PCV, pneumococcal conjugate vaccine (3 licensed formulations containing 7, 10 or 13 serotypes); RV, rotavirus vaccine (2 licensed formulations given as either 2- or 3-dose schedule); MMR, measles, mumps and rubella vaccine (a combined formulation with varicella vaccine (MMRV) is also licensed); MenCC, meningococcal C conjugate vaccine; dTpa, reduced antigen formulation of diphtheria–tetanus–acellular pertussis vaccine for adolescents and adults; HPV, human papillomavirus vaccine (both bivalent and quadrivalent HPV vaccines are licensed); IM, intramuscular; SC, subcutaneous.
* These antigens are currently given as a single injection as part of a hexavalent vaccine in infants in Australia and New Zealand, whereas HBV is not routinely used in the UK.
† May be given as a combined Hib–MenC conjugate vaccine (also used in the UK as a 2–4–12-month schedule).
‡ Varicella vaccine is given only where children have not previously received varicella vaccine and have no history of chickenpox.
§ This course of HBV (2 doses of adult formulation) is only for children not previously vaccinated against hepatitis B in infancy.
¶ Currently, HPV vaccine is only given to girls as a 3-dose schedule, but is also licensed for boys.
Vaccines are provided to registered immunization providers and generally are free of charge for children. Immunization providers are general practitioners, local authority immunization services, some hospital services (particularly in children’s hospitals), and some maternal and child health agencies. All immunization providers must be familiar with:
• vaccine storage and handling requirements
• requirements for informed consent for vaccine administration
• adverse effects of immunization
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
