Principle of Screening and Immunization

Question 1

define screening

Answer 1

• identification of unrecognized disease, disease precursors, or susceptibility to disease in persons without evidence of disease by rapidly applied tests, examinations or other procedures
• focuses on healthy populations, looks for asymptomatic disease
• positive or suspicious findings are referred for follow-up diagnostic tests and treatment

Question 2

give examples of screening tests

Answer 2

• questions
• clinical examinations
• laboratory tests
• genetic tests
• radiographic exam

Question 3

describe the intrinsic properties of a screening test

Answer 3

• reliability (reproducibility)
  
  • extent to which repeated measurements get similar results
• validity (accuracy)
  
  • ability of test to detect who has the disease and who does not
  • usually judged against another test of greater known accuracy (“gold standard”)
  • measured by sensitivity, specificity, predictive value of positive or negative test

Question 4

describe the function of the US Preventive Services Task Force

Answer 4

• independent panel of private-sector experts in primary care and prevention
• conducts rigorous, impartial assessments of the scientific evidence of effectiveness of clinical preventive services, including screening, counseling and preventive medications
• recommendations are the “gold standard”

Question 5

describe evidence-based medicine and recommendations

Answer 5

• the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients
• the practice of evidence-based medicine means integrating individual clinical expertise with the best available external clinical evidence from systematic research

Question 6

name 4 things evidence-based recommendations require

Answer 6

1. test or procedure is medically effective in reducing morbidity or mortality
2. medical benefits must outweigh the risks
3. cost of test or procedure must be reasonable
4. recommended actions must be practical and feasible

Question 7

list the selected recommended screening tests (USPSTF)

Answer 7

Question 8

describe smallpox (vaccine-preventable)

Answer 8

• variola major (more common) and minor forms
• mostly droplet spread
• incubation period ~12-14 days, then 2-4 day prodrome, then rash begins
• rash becoming blisters, all same stage
• ~30% case-fatality rate for variola major
• only communicable disease eradicated by human efforts

Question 9

name other vaccine-preventable rash illnesses

Answer 9

• chickenpox/varicella
• measles
• rubella/German measles

Question 10

name other vaccine-preventable childhood illnesses

Answer 10

• mumps (MMR)
• diphtheria (DTaP)
• pertussis/whooping cough (DTaP)

Question 11

name vaccine-preventable neuromuscular diseases

Answer 11

• poliomyelitis (IPV)
• tetanus (DTaP)

Question 12

describe passive immunity

Answer 12

• protection conferred to a susceptible host by transfer of immunity products from another person or animal
• temporary protection that wanes with time
• examples:
  
  • maternal antibodies across placenta or in milk
  • immune globulin
  • hyper-immune globulin
  • antitoxins
  • anti-venoms

Question 13

describe active immunity

Answer 13

• protection produced by the person’s own immune system (in response to non-self antigen)
• usually long-lasting (permanent)
• basic premise of immunization:
  
  • immunity and immunologic memory similar to natural infxn but without the disease

Question 14

describe live attenuated vaccines

Answer 14

• vaccine in which live “wild” virus is weakened (attenuated) through chemical or physical processes in order to process an immune response without causing clinical disease
• must replicate in the host to be effective
• immune response similar to natural infxn, and stronger than inactivated vaccines
• induce both humoral and CMI
• usually requires fewer doses*
  
  • *except those administered orally

Question 15

describe issues with live attenuated vaccines

Answer 15

• fragile–must be stored and handled carefully (for most, need to maintain cold chain)
• severe reactions possible, particularly in immunocompromised individuals
• interference from circulating antibody (e.g. measles vaccine and maternal antibodies)
• rarely, can convert back to virulent strain (e.g. OPV-associated polio)

Question 16

describe inactivated vaccines

Answer 16

• inactivated by heat or chemicals
• cannot replicate or revert
• generally not as effective as live vaccines
• less interference from circulating antibody than live vaccines
• fewer side effects (usually localized, if any)
• generally require 3-5 doses
• immune response mostly humoral
• antibody titer may diminish with time, requiring boosters

Question 17

describe combination vaccine, conjugate vaccine and adjuvant

Answer 17

• combination vaccine: combination of 2 or more vaccines (e.g. diphtheria/tetanus/pertussis)
• conjugate vaccine: vaccine in which a polysaccharide antigen is chemically joined with a protein molecule to improve the immunogenicity of the polysaccharide
• adjuvant: substance that is used in a vaccine to improve the immune response so that less vaccine is needed to produce a non-specific stimulator of the immune response

Question 18

describe a polysaccharide vaccine

Answer 18

• not consistently immunogenic in children < 2 yrs of age
• no booster response
• antibody with less functional activity
• immunogenicity improved by conjugation to a protein

Question 19

describe the schedule of vaccination in children

Answer 19

Question 20

describe recommended vaccinations in adolescents

Answer 20

Question 21

describe recommended vaccinations in adults

Answer 21