Vaccine resistance

Vaccine resistance is the evolutionary adaptation of pathogens to infect and spread through vaccinated individuals, analogous to antimicrobial resistance. It concerns both human and animal vaccines. Although the emergence of a number of vaccine resistant pathogens has been well documented, this phenomenon is nevertheless much more rare and less of a concern than antimicrobial resistance.

Vaccine resistance may be considered a special case of

Some of the causes advanced for less frequent emergence of resistance are[1]^[2] that

• vaccines are mostly used for
  prophylaxis
  , that is before infection occurs, and usually act to suppress the pathogen before the host becomes infectious
• most vaccines target multiple antigenic sites of the pathogen
• different hosts may produce different immune responses to the same pathogen

For diseases that confer long lasting immunity after exposure, typically

If vaccine resistance emerges the vaccine may retain some level of protection against serious infection, possibly by modifying the immune response of the host away from immunopathology.^[5]

The best known cases of vaccine resistance are for the following diseases

• animal diseases
  • Marek's disease where actually more virulent strains emerged after vaccination^[6][7] because the vaccine did not protect against infection and transmission, only against serious forms of the disease
  • Yersinia ruckeri^[8][9] because a single mutation was sufficient to generate vaccine resistance
  • avian metapneumovirus^{[10][11][12][13]}
• human diseases
  • Streptococcus pneumoniae^[14][15] because recombination with another serotype not targeted by the vaccine
  • hepatitis B virus^{[16][17][18][19]} because the vaccine targeted a single site formed by 9 amino acids
  • acellular vaccines
    targeted only a few antigens