IB DP Biology: HL复习笔记11.1.4 Smallpox Vaccine & Eradication

Introduction

• The principles underpinning vaccinations were discovered by Edward Jenner in the 1700s when he developed the first smallpox vaccine
• Smallpox was a highly infectious disease caused by the variola virus which first emerged thousands of years ago
  • Notable symptoms of smallpox included fever and an extensive rash with pus filled pustules
  • Long term effects included scarring and blindness
  • There was a 30% death rate in those who contracted the disease
• Variolation was a method used to try and protect people from the most serious symptoms
  • Variolation involved scratching material from smallpox pustules into the arms of patients
  • Symptoms resulting tended to be less serious than those of naturally infected patients
    • The pustules tended to contain pus, a substance that contains dead white blood cells and destroyed pathogens
    • Sometimes the pus contained functional pathogens so variolation could still cause disease and death.
• Edward Jenner observed that milkmaids who had been exposed to cowpox were showing a level of immunity to smallpox
• He hypothesised that they were protected due to their exposure to the cowpox virus which was similar but less serious
• Jenner combined his observations and the method of variolation to develop a cowpox inoculation which he tested on a 9 year old boy
  • He took pus from the skin lesions caused by cowpox and scratched it into the skin of a patient
• The inoculation proved successful; when Jenner later attempted to infect the boy with the variola virus no illness developed

NOS: Consider ethical implications of research; Jenner tested his vaccine for smallpox on a child

• There are many topics of interest in scientific fields which have significant ethical implications
• In the modern-day there are procedures in place that set the criteria to ensure that ethical decisions are made and ethical procedures are followed whilst working within controversial and sensitive scientific topic areas
• This consideration of ethics in science has been developed over time and with the establishment of working groups such as the World Health Organisation
• Edward Jenner carried out primitive investigations into vaccinations in 1790 when there was no existence of a Research Ethics Committee as there is now
  • He did his first tests without any initial laboratory research or animal testing
  • His first patient was a small boy who he exposed to the deadly smallpox virus in the hope that his vaccination would work
• Under current legislation, Jenner's methods would not be approved or even considered by an ethical review committee

• Herd immunity is one approach to protecting populations from diseases
  • Herd immunity arises when a sufficiently large proportion of the population has been vaccinated (and are therefore immune) which makes it difficult for a pathogen to spread within that population
  • Those who are not immunised are protected and unlikely to contract it as the levels of the disease are so low
• Smallpox emerged thousands of years ago but outbreaks occurred periodically for many years afterwards and was still widespread as late as 1966 in South Africa, Africa and Asia.
• The WHO began an eradication programme against Smallpox in 1967, stating their intention to eradicate the virus within ten years
• The WHO did not declare smallpox eradicated until 1980
• The programme focused on:
  • Vaccination
    • The aim was to vaccinate more than 80% of populations at risk
    • If a case of smallpox was reported, ring vaccination would occur
    • This is where everyone in the household with the reported case, the surrounding 30 households, relatives and anyone else who had contact would get vaccinated
  • Surveillance
• The success of the program was attributed to the following factors:
  • The virus was stable – it did not mutate therefore its surface antigens did not change, therefore the same vaccine could be used worldwide which made it cheap to produce the vaccine
  • The vaccine was a ‘live attenuated’ version, being produced from a harmless strain of a similar virus
  • The vaccine could be transported without becoming unviable, as it could be freeze-dried and kept at high temperatures for up to 6 months, thus it was suitable for the tropics
  • The smallpox variola virus only infects humans so was easily traced and monitored (compared to other diseases which re-emerged after being masked within animal populations)
  • Symptoms were obvious and developed quickly so vaccination of close contacts was effective in preventing human to human transmission
  • Vaccination gave long lasting immunity so reinfection was unlikely