Vaccinations

last authored: October 2009, David LaPierre

 

Introduction

Vaccination, or immunization, is the administration of antigen to develop an immune response, including cellular activation and antibody production, in order to prevent subsequent infection. The term vaccine, derived from latine for cow, was coined by Pasteur in honour of Edward Jenner's work with cowpox.

 

Specific Vaccines

Viruses hepatitis A and B influenza A and B (trivalent) MMR (measles, mumps, rubella) varicella (chickenpox) HPV rotavirus

Bacteria meningococcal pneumococcal vaccine (Prevnar) diptheria pertussis CRS tetanus invasive H. infuenza

 

 

Vaccine Schedules

Premature infants should receive vaccinations based on their chronological age, regardless of birthweight, not calculated age. THe exception is hepatitis B, which should not be given under 2 kg.

 

Various locales have differing vaccination policies. Some of these include:

 

 

Types of Vaccines

 

Live vaccines

• Most effective vaccine, made from live pathogens that have been somehow attenuated to make them non-pathogenic but can still replicate
• Effectiveness due to the fact that organism persists for longer periods, and multiple epitopes present
• Can, on rare occasions, revert to become pathogenic again

Live vaccines in use include oral polio (primarily in developing countries), varicella, MMR, yellow fever, oral typhoid, and BCG against TB; used in confined populations during outbreaks.

 

Killed Vaccines

• safer, but less effective than live vaccines; booster doses often required, along with adjuvants.
• offer many epitopes, in contrast to sub-unit vaccines
• examples: influenza, rabies, whole cell pertussis

Isolated protein vaccines (subunit)

• well-characterized, customizable
• require adjuvants, such as aluminum, to enhance inflammatory response
  • liposomes may circumvent need for adjuvants by enhancing APC uptake
• isolated vaccines essential for immunization against toxins (toxoids), ie tetanus and diptheria, hepatitis B, pertussis

DNA (Vector) vaccines

• hybrid DNA, using live virus/bacterial vector and inserted gene of interest
• small spectrum of antigens, and disappointing response

Polysaccharide vaccines

• You'd think IgG response requires T cell response and class switch, which occurs only with peptide antigen
• PS vaccines do work over age 3, likely through formation of chimeric haptens
• Conjugated vaccines of capsule proteins for H. influenzae (Act-Hib) and S. pneumoniae (Prevnar) work for infants 2 months and up, through require boosting

Passive vaccines

• contain immunoglobulins designed to kill or attenuate pathogen. These include human blood products or monoclonal antibodies. Antivenom is an example.

Passive vaccines protect for approx. one month.

The effect of injecting immunoglobulin was first discovered in the late 1800s. Since then, Passive immunization has become standard practice in many cases.

 

 

Preparation of Immunoglobulin

Passive immunizations are prepared from the pooled plasma of thousands of donors, representing a sample of anitbodies that respond to a broad variety of pathogens. A gram of intravenous immunoglobulin (IVIG) may contain 10¹⁸ molecules of IG - mostly IgG and may represent up to 10⁷ different antibody specificities.

Patients often receive 200-400 mg per kg, meaning a 70 kg man would receive 14-28 g every 3-4 weeks.

IVIG is treated exhaustively with solvents and detergents to reduce the risk of infectivity and to reduce aggregates that might trigger massive activation of the complement pathway and subsequent anaphylaxis.

Effects of IVIG

One of the most important uses of administered antibody is the recruitment of the complement pathway to destroy pathogens. Opsonization will target pathogens for phagocytosis, and toxins will be neutralized. Antibody-dependent cell-mediated cytotoxicity (ADCC) by NK cells also occurs.

Uses of IVIG

IgG is given to immunocompromized patients both IM and IV.

IgG given to healthy people

RSV IgG given to premature babies

given if risk of tetanus without recent booster

rabies if bitten

anti-venom

 

 

 

Vaccine Safety

As with almost all health interventions, vaccines carry benefits and risks. As they are usually given to healthy people to prevent disease, they are held to a higher standard of safety.

 

Immediate Reactions

The most common adverse event is local injection site pain, lasting <48 hours. The MMR is especially painful.

Systemic reactions such as fever are less common, and must be reported by physicians to ensure safety for others.

Causality of other events is more difficult to prove.

• no relationship: vaccine given at peak time for SIDS
• trigger: febrile seizure following infant immunization
• causal relationship: paralysis caused by oral polio vaccine

unlikely links:

• HBV and multiple sclerosis
• MMR and autism
• HBV and SIDS

 

Contraindications

Minor illnesses, such as the common cold, with or without fever, are NOT contraindications for immunization. However, moderate or severe illness precludes vaccination.

 

Other contraindications include:

• live vaccine in an immunocompromised person
• previous anaphylactic response
• known anaphylactic response to a vaccine constituent (ie eggs)
• preganancy and live vaccines

 

 

Vaccine Education

Canadian Pediatric society has a website for parents: Caring For Kids

 

Resources and References

• Canada Immunization Guide
• US CDC Vaccines and Immunizations
• PHAC's vaccine safety resource materials
• Canadian Coalition for Immunization Awareness and Promotion