Breakthrough measles

Breakthrough measles (reinfection)

The term 'breakthrough measles' (previously referred to as 'reinfection') 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 measles containing vaccine.

• cases of breakthrough measles are generally mild, have a shorter duration and may not have the full triad of cough, coryza and conjunctivitis
  • in some cases of breakthrough measles a typical rash may not be observed.

The immunological characteristics of breakthrough measles differ from those of primary vaccine failure, which is thought to occur when patients never develop immunity, for example when measles vaccine is given in the presence of maternal antibody

• in contrast, breakthrough measles cases are thought to arise when antibody levels from past immunity wane, usually after many years, and subsequent close exposure can lead to measles viral replication and a consistent illness.

Breakthrough measles cases are usually seen in patients who have received 2 doses of measles-containing vaccine, and antibody testing may be misinterpreted

• infectivity of these cases is lower than in primary measles infection, and transmission from breakthrough measles is rare, probably due to low and transient infectivity
  • for this reason, tracing the contacts of presumed breakthrough measles can be limited to those at highest risk of complications and/or with a very high level of exposure.

In measles endemic areas breakthrough cases represent fewer than 10% of total infections, but this will increase as vaccination coverage in the general population rises (2)

In a highly vaccinated population and with the increasing availability of PCR testing it is inevitable that more breakthrough measles infections will be identified

• for example it is not unusual to pick up breakthrough infections in outbreaks linked to healthcare or other settings through active case finding
  • it is important to note that breakthrough measles is not thought to pose a significant public health threat in the context of global measles elimination efforts

Reference:

• Public Health England (November 2019). National measles guidelines.
• UK Health Security Agency (February 2024). National measles guidelines