Vaccines

Immunity

Specific defensesImmunity

Passive immunityActive immunity

Following clinical infection

Following subclinical infection

Following vaccination Following administration ofImmunoglobulin or antiserum

Transfer of maternal Antibodies Through milk

Transfer of maternal Antibodies Through placenta

natural

acquired

Active immunity

• Resistance developed in response to stimulus by an antigen (infecting agent or vaccine) and is characterized by the production of antibodies by the host.

Passive immunity

• Immunity conferred by an antibody produced in another host. It may be acquired naturally or artificially (through an antibody-containing preparation).

Immunizing agents

Immunizing agents

antiseraimmunuglobulinsvaccines

Vaccination

• Vaccination is a method of giving antigen to stimulate the immune response through active immunization.

• A vaccine is an immuno-biological substance designed to produce specific protection against a given disease.

• A vaccine is “antigenic” but not “pathogenic”.

Let’s go back in time to seehow this strategy works

The time: 500 B.C.The place: Greece

Even 2,500 Years Ago, People Knew Immunity Worked.

• Greek physicians noticed that people who survived smallpox never got it again.

• The insight: Becoming infected by certain diseases gives immunity.

Fast forward 2300 years

pathmicro.med.sc.edu/ppt-vir/vaccine.ppt

I had a brilliant idea

Vaccination• Charles Jenner 1796 : Cowpox/Swinepox• 1800’s Compulsory childhood vaccination

Smallpox

•1% v. 25% mortality•Life-long immunity• UK: 1700’s• China 1950• Pakistan/Afghanistan/ Ethiopia 1970

pathmicro.med.sc.edu/ppt-vir/vaccine.ppt

• No animal reservoir

• Lifelong immunity

• Subclinical cases rare

• Infectivity does not precede overt symptoms

• One serotype

•

pathmicro.med.sc.edu/ppt-vir/vaccine.ppt

Smallpox presented many advantages that made this possible

As a result, after a world-wide effortSmallpox was eliminated as a human disease in 1978

pathmicro.med.sc.edu/ppt-vir/vaccine.ppt

Types of vaccines

• Live vaccines• Attenuated live vaccines• Inactivated (killed vaccines)• Toxoids• Polysaccharide and polypeptide (cellular

fraction) vaccines• Surface antigen (recombinant) vaccines.

Live vaccines

• Live vaccines are made from live infectious agents without any amendment.

• The only live vaccine is “Variola” small pox vaccine, made of live vaccinia cow-pox virus (not variola virus) which is not pathogenic but antigenic, giving cross immunity for variola.

Live attenuated (avirulent) vaccines

• Virulent pathogenic organisms are treated to become attenuated and avirulent but antigenic. They have lost their capacity to induce full-blown disease but retain their immunogenicity.

• Live attenuated vaccines should not be administered to persons with suppressed immune response due to:– Leukemia and lymphoma– Other malignancies– Receiving corticosteroids and anti-metabolic agents– Radiation– pregnancy

Live Attenuated Vaccineshave several advantages

• Attenuated (weakened) form of the "wild" virus or bacterium

• Can replicate themselves so the immune response is more similar to natural infection

• Usually effective with one dose

Live Attenuated Vaccinesalso have several disadvantages

• Severe reactions possible especially in immune compromised patients

• Worry about recreating a wild-type pathogen that can cause disease

• Fragile – must be stored carefully

MMWR, CDC

A number of the vaccines you receivedwere live Attenuated Vaccines

• Viral measles, mumps,rubella, vaccinia, varicella/zoster,

yellow fever, rotavirus, intranasal influenza, oral polio

• Bacterial BCG (TB), oral typhoid

Inactivated (killed) vaccines

• Organisms are killed or inactivated by heat or chemicals but remain antigenic.

• They are usually safe but less effective than live attenuated vaccines.

• The only absolute contraindication to their administration is a severe local or general reaction to a previous dose.

Inactivated Vaccines

• Cannot replicate and thus generally not as effective as live vaccines

• Usually require 3-5 doses• Immune response mostly antibody based

Minuses

Inactivated Vaccines

• No chance of recreating live pathogen• Less interference from circulating antibody than

live vaccines

Pluses

Inactivated Vaccines are alsoa common approach today

• Viral polio, hepatitis A, rabies, influenza*

• Bacterial pertussis*, typhoid*cholera*, plague*

Whole-cell vaccines

*not used in the United States

Other Inactivated Vaccinesnow contain purified proteins

rather than whole bacteria/viruses

• Proteins hepatitis B, influenza,acellular pertussis,human papillomavirus, anthrax, Lyme

• Toxins diphtheria, tetanus

Sabin Polio VaccineAttenuated by passage in foreign host (monkey kidney cells)

Selection to grow in new host makes virus

less suited to original host

Sabin Polio VaccineAttenuated by passage in foreign host (monkey kidney cells)

Selection to grow in new host makes virus

less suited to original host

• Grows in epithelial cells• Does not grow in nerves• No paralysis •Local gut immunity (IgA)

Salk Polio Vaccine

• Formaldehyde-fixed• No reversion

US: Sabin attenuated vaccine

~ 10 cases vaccine-associated polio per year =

1 in 4,000,000 vaccine infections

Scandinavia: Salk dead vaccine• No gut immunity• Cannot wipe out wt virus

Polio Vaccine illustrates the pluses and minuses of live vaccines

pathmicro.med.sc.edu/ppt-vir/vaccine.ppt

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Killed (Salk) Vaccine

Live (Sabin) Vaccine

Live virus generates a more complete immune response

Modern molecular biologyhas offered new approaches to make vaccines

1. Clone gene from virus or bacteriaand express this protein antigenin yeast, bacteria or mammalian cells in culture

Modern molecular biologyhas offered new approaches to make vaccines

2. Clone gene from virus or bacteriaInto genome of another virus (adenovirus, canary pox, vaccinia)And use this live virus as vaccine

Cloned protein antigenshave pluses and minuses

Pluses•Easily manufactured and often relatively stable•Cannot “revert” to recreate pathogen

Minuses• Poorly immunogenic• Post-translational modifications• Poor CTL response

Viral vectors have pluses and minuses

Pluses• Infects human cells but some do not replicate• Better presentation of antigen• Generate T cell response

Minuses•Can cause bad reactions•Can be problems with pre-exisiting immunity to virus•Often can only accommodate one or two antigens

Toxoids

• They are prepared by detoxifying the exotoxins of some bacteria rendering them antigenic but not pathogenic. Adjuvant (e.g. alum precipitation) is used to increase the potency of vaccine.

• The antibodies produces in the body as a consequence of toxoid administration neutralize the toxic moiety produced during infection rather than act upon the organism itself. In general toxoids are highly efficacious and safe immunizing agents.

Polysaccharide and polypeptide (cellular fraction) vaccines

• They are prepared from extracted cellular fractions e.g. meningococcal vaccine from the polysaccharide antigen of the cell wall, the pneumococcal vaccine from the polysaccharide contained in the capsule of the organism, and hepatitis B polypeptide vaccine.

• Their efficacy and safety appear to be high.

Surface antigen (recombinant) vaccines.

• It is prepared by cloning HBsAg gene in yeast cells where it is expressed. HBsAg produced is then used for vaccine preparations.

• Their efficacy and safety also appear to be high.

Types of vaccinesLivevaccines

LiveAttenuated vaccines

KilledInactivated vaccines

Toxoids Cellular fraction vaccines

Recombinant vaccines

•Small pox variola vaccine

•BCG•Typhoid oral•Plague•Oral polio•Yellow fever•Measles•Mumps•Rubella•IntranasalInfluenza•Typhus

•Typhoid•Cholera•Pertussis•Plague•Rabies•Salk polio•Intra-muscular influenza•Japanise encephalitis

•Diphtheria•Tetanus

•Meningococcal polysaccharide vaccine•Pneumococcal polysaccharide vaccine•Hepatitis B polypeptide vaccine

•Hepatitis B vaccine

Routes of administration

• Deep subcutaneous or intramuscular route (most vaccines)

• Oral route (sabine vaccine, oral BCG vaccine)• Intradermal route (BCG vaccine)• Scarification (small pox vaccine)• Intranasal route (live attenuated influenza

vaccine)

Scheme of immunization

• Primary vaccination– One dose vaccines (BCG, variola, measles, mumps,

rubella, yellow fever)– Multiple dose vaccines (polio, DPT, hepatitis B)

• Booster vaccinationTo maintain immunity level after it declines after

some time has elapsed (DT, MMR).

Periods of maintained immunity due to vaccines

• Short period (months): cholera vaccine• Two years: TAB vaccine• Three to five years: DPT vaccine• Five or more years: BCG vaccine• Ten years: yellow fever vaccine• Solid immunity: measles, mumps, and rubella

vaccines.

Levels of effectiveness

• Absolutely protective(100%): yellow fever vaccine• Almost absolutely protective (99%): Variola, measles,

mumps, rubella vaccines, and diphtheria and tetanus toxoids.

• Highly protective (80-95%): polio, BCG, Hepatitis B, and pertussis vaccines.

• Moderately protective (40-60%) TAB, cholera vaccine, and influenza killed vaccine.