Vaccination Problems

Question 1

define herd immunity

Answer 1

level of immunity required in a population to prevent infectious disease transmission

Question 2

how do you achieve herd immunity via vaccination?

Answer 2

prioritize vaccination based on structure; the idea is to connect nodes so there is no path from unvaccinated node to unvaccinated node

1. vaccinate nodes central to the network (those leading to many other nodes)
2. vaccinate highly connected nodes

conditions that must be met:
1. disease agent restricted to single host species
2. direct transmission
3. vaccine induces solid immunity

Question 3

describe determinants of disease outbreaks

Answer 3

1. number of susceptible individuals that can become infected
2. contact rate: how many contacts an infected individual has in a given time period
3. basic reproduction number (R0): average number of secondary infections generated by an infectious individual in a completely susceptible population
   R0 = probability of transmission x duration of infectiousness x average # of contacts per unit time
   -R0<1: no sustained transmission
   -R0 approx 1: disease minimally sustained
   -R0>1: sustained transmission

REMEMBER: absence of infection does NOT mean absence of outbreak risk

Question 4

relate R0 to herd immunity

Answer 4

the proportion of the population that needs to be immunized to achieve herd immunity = 1 - 1/R0

outbreaks are easier to control with a lower R0

Question 5

list factors impacting herd immunity

Answer 5

1. waning immunity: need for boosters
2. population changes (influx of susceptible individuals)
   -babies
3. changes in pathogen (mutations)
4. pockets of susceptible individuals