Vaccine effectiveness in providing immunity against measles

Vaccine effectiveness:

• based on available evidence, vaccination with one dose of the MMR vaccine is at least 95% effective in preventing clinical measles and 92% effective in preventing secondary cases among household contacts (1)
• are 2 main types of vaccine failure:
  • primary failure occurs when an individual fails to make an initial immunological response to the vaccine
    • primary vaccine failure is rare; it can occur (particularly after a single dose)
    • in settings with high levels of close interpersonal contact, such as large households or school settings, controlling measles outbreaks requires a high coverage of 2 doses of MMR
  • secondary failure occurs when an individual responds initially, but then protection wanes over time
• the term ‘breakthrough measles’ (previously referred to as ‘reinfection’, or secondary vaccine failure) is used to describe a confirmed case of measles in someone who developed immunity to measles, either from natural measles or from prior receipt of a measles-containing vaccine, typically between 6 and 30 years after infection or immunisation (1)
  • usually associated with intense and/or prolonged exposure to an infected individual, for example, directly caring for an acutely ill person, and so is generally only seen in healthcare workers or in household settings
  • in breakthrough measles, symptoms are generally mild
    • conjunctivitis is generally absent
    • rash may not follow typical progression
    • duration of measles illness tends to be shorter
    • infectivity of these cases is much lower and transient, unlike primary measles infection
      • although polymerase chain reaction (PCR) positive, the presence of neutralising antibodies in respiratory secretions greatly reduces the infectiveness of the virus

Reference:

1. UK Health Security Agency (February 2024). National measles guidelines.