Immunization

• COVID-19 PANDEMIC
• Regina Oladokun, Professor of Paed ID, COMUI/UCH, Ibadan
• Immunisation in Childhood
• Immunity


  Ability to fight disease or ability of the body to tolerate material that is indigenous to it and eliminate material that is foreign
• Immune system


  Comprises organs and specialized cells that protect the body by identifying harmful substances (antigens) and destroys them using antibodies and other specialized substances and cells
• Ways immunity is acquired


  • Previous infection (Chicken pox, measles, subclinical polio)
  • Immunisation (with vaccines)
• Immunisation


  The act of artificially inducing immunity or providing protection from a particular disease
• Vaccines


  Stimulate the immune system of an individual to help avoid getting an infection or disease
• Artificial induction of immunity (vaccination) antedated understanding of the germ theory of disease
• Edward Jenner discovered that milk maids who had contracted cowpox were protected against small pox, and inoculated fluid from cowpox lesions into the skin of susceptible individuals to induce protection against smallpox, thus immunization was born


  1796
• Immunisation is the most cost-effective means of preventing infectious diseases (the second is sanitation)
• Immunisation averts 2 - 3 million deaths every year, and an additional 1.5million if immunization coverage improves
• Effective immunisation led to the eradication of smallpox globally, near-eradication of polio worldwide, and significant reduction in Vaccine-preventable diseases (VPDs) in children
• Active immunisation


  Usually accomplished by the administration of vaccine that stimulates the body's immune system to produce antibody or cell mediated immunity or both thereby protecting against the infectious agent
• Passive immunisation


  Consists of providing temporary protection through the administration of exogenously produced antibody
• Situations in which passive immunisation commonly occurs


  • Transplacental transfer of antibodies to the fetus which may provide protection against certain disease for the first 3 to 6months of life
  • Injection of immunoglobulin for prevention of specific infections, e.g. hepatitis B immune-globulin, tetanus immune globulin
• Constituents of Immunising agents


  • Suspending fluid: sterile water, saline, or complex fluid containing small amounts of protein or other constituents derived from the medium or biologic system in which the immunizing agent is produced
  • Preservatives, stabilizers, and antibiotic to inhibit bacterial growth in viral culture or the final product, stabilize the antigen, and prevent allergic reactions
  • Adjuvant - Compounds used to enhance immunogenicity e.g. An Aluminum salt
• Determinants of Immunogenicity


  • Vaccine related: chemical and physical state of the antigen, dose of the antigen given, timing, presence of adjuvant, route of administration
  • Child related: genetic characteristics of the child, age, nutrition, infection, immune status
• Types of vaccines


  • Live attenuated vaccines
  • Inactivated vaccines
  • Polysaccharide vaccines
  • Recombinant vaccines
• Live attenuated vaccines


  Derived from disease-causing viruses or bacteria weakened under lab conditions, grow in a vaccinated individual but will not cause an clinical disease, only one dose usually required to provide life-long immunity, with the exception of those administered orally e.g. oral polio vaccines (multiple doses required)
• Currently available live attenuated vaccinesare what ?

• Inactivated vaccines


  Produced by growing viruses or bacteria in culture media and inactivated (killed) with heat or chemicals, do not grow in the vaccinated individual, therefore will not cause disease, not as effective as life vaccines, will usually require multiple doses for full protection
• Types of inactivated vaccines


  • Whole-cell vaccines: Made of an entire bacterial or viral cell
  • Fractional vaccines: Protein-based or polysaccharide-based
• Inactivated vaccines


  Generally, the first dose does not produce protective immunity, but "primes" the immune system, protective immune response develops after 2nd or 3rd dose, antibody titers against inactivated antigens decrease with time, some inactivated vaccines may require periodic supplemental doses to increase or "boost," antibody titers
• Currently available whole-cell inactivated vaccines

  • Viral vaccines: Polio, rabies, and hepatitis A
  • Fractional vaccines: Subunits: Hepatitis B, acellular pertussis, Toxoids: Diphtheria, tetanus
• Polysaccharide vaccines


  Unique type of inactivated subunit vaccine composed of long chains of sugar molecules that make up the surface capsule of certain bacteria, not very immunogenic
• Diseases with available polysaccharide vaccines

  • Pneumococcal disease (Pneumococcal Polysaccharide Vaccine)
  • Meningococcal disease
  • Salmonella Typhi
• Recombinant vaccines


  Produced by genetic engineering technology, by inserting genetic material from a disease-causing organism into a harmless cell, which replicates the proteins of the disease-causing organisms, the proteins are then purified and used as vaccine
• Guiding principles in planning for immunization in a community


  • Epidemiology of the disease, immunization is usually given in terms of priority to children and others at risk, age-specific morbidity and mortality, recommended in special circumstances, to control outbreaks of diseases, routes of immunization
• Herd Immunity


  The level of resistance of a community or group of people to a particular disease, occurs through clinical or sub clinical infection in the community or high and continuous immunization rate, occurs when a critical % of the population is vaccinated (around 80%), creating an immunological barrier that reduces the spread of disease in the community, with sufficiently high herd immunity, occurrence of an epidemic is unlikely and the disease may eventually be eliminated
• As a result of the impressive success of the smallpox eradication programme, WHO looked for other ways to build on the achievement and in 1974, the Expanded Programme on Immunization (EPI) was created
• The EPI originally aimed to protect children against 6 killer diseases, and was adopted globally (TB, Polio, Tetanus, Diphtheria, Pertussis and Measles)
• Since then, WHO has recommended new vaccines for inclusion in immunization programmes, including yellow fever in 1986 (for Africa only), hepatitis B in 1992, Hib in 1997 (according to national capacities and priorities) up to HPV
• Nigeria launched the EPI in 1978, but recorded low immunization coverage in all parts of the country due to low public mobilization and awareness, and poor maintenance of the cold chain
• By 1990, a high level of coverage of 80% was achieved in some areas but was not maintained due to poor implementation, continuing economic recession, political instability and withdrawal of foreign donors from the programme, and inadequate, irregular supply of vaccines and poor utilization of immunization services
• In 1996, the Federal Government of Nigeria organized a review of the immunization programme and re-launched it as the National Programme on Immunization (NPI), to reflect national commitment and ownership
• Strategies for Immunisation


  • Routine immunisation (RI)
  • Supplemental immunisation
• Routine immunization (RI)


  An outlined program for immunising children at appropriate ages in a specific environment, strategies for the routine delivery of immunisation services include fixed facility (within 5km radius), outreach, and mobile
• Current Routine Immunisation Schedule-Nigeria


  • At birth: BCG, OPV0, Hep B0
  • 6 weeks: Pentavalent 1, PCV1, OPV1, IPV1
  • 10 weeks: Pentavalent 2, PCV2, OPV2
  • 14 weeks: Pentavalent 3, PCV3, OPV3, IPV2
  • 6 months: Vitamin A 1st dose
  • 9 months: Measles 1st
• Intramuscular


  Route of administration where the vaccine is injected into the muscle