Vaccine History and Acquired Immunity

Vaccines Overview

• Vaccines cover the history of immunization, modern vaccines, and vaccine development.

Acquired Immunity

• In 430 B.C.E., Thucydides described how individuals who recovered from a plague epidemic in Athens were then free from apprehensions because they would not be attacked a second time, or not with a fatal result.

History of Vaccines

• Jenner's Smallpox Vaccine addressed a highly contagious disease with a high fatality rate (20-40%).
• Smallpox caused 500 million deaths in 20th century.
• Variolation involved scarifying unimmunized individuals with a tiny amount of material from diseased patients, practiced in China and the Middle East, and 2-3% of those variolated would not be protected and died.
• Vaccination involved scratching a pustule from an infected individual (milkmaid) with cowpox against the skin.
• The vaccination conferred some cross-protection to subsequent exposure to smallpox, 1% were not fully protected, BUT lesions that did develop were not as severe.

Benefits of Vaccines

• Vaccines are much cheaper than the cost of treatment.
• They reduce suffering and long-term consequences of diseases like polio, which can cause permanent paralysis.
• Vaccines protect against diseases with no effective therapy.

Shortage of Vaccines

• Financial constraints, especially for developing world problems, and legal concerns over litigation, particularly blaming vaccines for autism, are a barrier.
• There are also political factors.

Ideal Vaccine Characteristics

• An ideal vaccine must be safe with minimal adverse side effects.
• It should be efficacious, able to elicit a strong and long-lasting protective immune response.
• It must be readily delivered in combination with other vaccine components.
• For mucosal pathogens, it should be effective when administered orally or intranasally.
• The vaccine should be heat-stable, dry-stable, and have a long shelf life.
• It should be low-cost and easy to manufacture and administer with minimal infrastructural requirements.
• An ideal vaccine requires minimal maintenance programs, where fewer boosters increase compliance.

Good Antigen Properties

• Important factors include where the pathogen encounters occur, either Mucosal sites (sIgA) or Systemic (IgM; IgG).
• Major virulence factors include toxins, capsules, and adhesins.
• A key consideration is how much antigenic variation exists, measured by the number of serotypes.
• It is important to consider if the antigen mimics host antigens, and the potential for non-response or autoimmunity.
• Whether the pathogen is extracellular or intracellular determines if Humoral or Cell-mediated immunity is needed.

Stages of Immunization Program

• When worry about disease diminishes, attention focuses on issues related to vaccine safety.

Vaccination Reasons

• Vaccination confers protection to the individual and protects public health.
• Collective immunity through mass immunization confers indirect protection on the nonimmune members.
• It is an important force in preventing epidemics.

Herd Immunity

• COVID-19 R0 = 2.2-2.7 or 5.7, 1-1/2.2 or 1-1/2.7 = 55-63%.
• The classical formula for calculating Herd immunity threshold is 1–1/R0.

R0 Definition

• R0 is the average number of people who will contract a contagious disease from one person with that disease.
• It refers to a population previously free of infection and unvaccinated.

Barriers to Vaccine Success

• There are many childhood vaccines, so the solution is to combine them into one shot (Pediarix = DTaP, Polio, Hep B).
• Similar threshold of safety criteria as seen for antibiotics, plus elevated concern that most vaccines are targeted to children.
• The threat of lawsuits has disengaged some companies from investing in vaccine development.
• Vaccine successes are their own downfall where elimination of deadly diseases makes people forget the impact that vaccines have.
• Technical barriers exist because some pathogens have outsmarted measures.

Eradication of Diseases

• Human-specific diseases, with no animal reservoir or vectors, makes eradication easier.
• Rapid identification and epidemiologic tracing, lifelong immunity after exposure, and international commitment to eradication are important.

Smallpox Mandatory

• There were scenes of policemen holding down men in their night robes while vaccinators began their work on their arms.
• Inspectors were going room to room looking for children with smallpox and if they found them, they were literally tearing babes from their mothers' arms to take them to the city pesthouse [which housed smallpox victims.]"

Anti-Vaccine Movement

• In 1736, Benjamin Franklin lost one of his Sons, a fine Boy of 4 Years old, taken by the Small Pox in the common way.
• He regretted that he had not given it to him by inoculation, for the Sake of Parents, who omit that Operation on the Supposition that they should never forgive themselves if a Child died under it.
• He said that Regret may be the same either way, and therefore the safer should be chosen.