Imperfect Vaccination Can Enhance the Transmission of Highly Virulent Pathogens

Contributed by Ione Murphy
Imperfect Vaccination Can Enhance the Transmission of Highly Virulent Pathogens
"Our data show that anti-disease vaccines that do not prevent transmission can create conditions that promote the emergence of pathogen strains that cause more severe disease in unvaccinated hosts."
"Thus, the use of leaky vaccines can facilitate the evolution of pathogen strains that put unvaccinated hosts at greater risk of severe disease. The future challenge is to identify whether there are other types of vaccines used in animals and humans that might also generate these evolutionary risks."
Vaccine - The evolutionary consequences of vaccination
"Pathogens often have the potential to evolve very rapidly, because of their short generation times, large population sizes and high rates of mutation. It is now commonly believed that use of vaccines will typically result in novel selective pressure on pathogen populations, often resulting in the emergence of resistant
"Scientists have found a new strain of polio virus that is thought to be responsible for the major epidemics of polio cases in the recent times. This polio virus is not affected by polio vaccines.
Initially, researchers thought that low vaccine coverage was the cause of newly reported cases, but now they have found mutations in viruses that are making them resistant to conventional polio vaccines." 
Could the human papillomavirus vaccines drive virulence evolution?
"The evolutionary responses of viruses to vaccines are of serious concern, and they may appear several years after the introduction of such control measures [49]. In a review, Read & Mackinnon contrast successful vaccines that stimulate natural immunity with novel vaccines that stimulate new responses that differ considerably from natural immunity. They warn that imposing new effector mechanisms can create very different selection pressures, with potentially unwanted consequences"
Rotavirus- "Whether the widespread use of these vaccines will introduce selective pressures on human RVs, triggering genetic and antigenic changes that undermine the effectiveness of vaccinations programs, is uncertain and will require continued surveillance of human RVs. Since selective pressures coming from the vaccine may be subtle, it could be many years before they are apparent. However, a recent analysis of children with RV diarrhea in Nicaragua, a country that exclusively vaccinates with RotaTeq, showed that two children shed G1P[8] viruses that contained an NSP2 gene identical in sequence to that of RotaTeq "
"Pertussis resurgence was associated with a mutation in the gene coding for fimbrial proteins, although the functional role of that mutation remains unclear [76]. Based on the above observations, it has been proposed that vaccination has resulted in selection of more virulent strains that are more efficiently transmitted by previously primed hosts [69]." 
Influenza- "These findings offer new insight into the mechanism of how selection pressure as a result of vaccination could contribute to the virus evolving into a more infectious strain by generating better-binding HA proteins "
Hepatitis B:
"Immunologists discovered mutated vaccine-resistant viruses were causing disease" 
"The virus is always evolving and mutating, and new viruses will emerge," He said. "It's only a matter of time until the old vaccine we have doesn't work."
Pneumonia, Meningitis Evolving To Evade Vaccines.
"These life-threatening pathogens are capable of evolving rapidly and developing genetic decoys that serve to disguise them from even the most powerful drugs."
Mutations in the H, F, or M Proteins Can Facilitate Resistance of Measles Virus to Neutralizing Human Anti-MV Sera..