This effectively plugged the immunity gap revealed by the outbreak and confirmed serologically. The nature of outbreaks can also highlight health service deficiencies permitting the spread of measles amongst vulnerable non-immune groups.

This was a particular feature of recent outbreaks in a number of countries that have interrupted endemic measles transmission, including the Republic of Korea, Australia and the USA [28], [29] and [30]. A common feature of these outbreaks was measles predominantly occurring in young children, most too young to be immunised or only having received a single measles vaccine dose, with nosocomial spread due to deficiencies in infection control. In all cases measures were taken to strengthen triage and isolation practices, PF-06463922 cost and promote the vaccination of health care staff. Compared with polio, elimination of measles relies more heavily on strong routine services both because of the requirement to reach all communities with such high coverage, and because the vaccine is delivered by injection. A valuable epidemiological measure of an infectious agent’s transmissibility is its basic reproduction number (R0) – the average number of secondary cases generated by AZD9291 concentration a primary case in a completely susceptible population. Measles is the most infectious communicable disease known with

a R0 of 12–18 [31] and [32]. This infectiousness poses a massive challenge to elimination as in most settings 95% or more of the population will need to be immune to ensure adequate herd immunity to prevent or contain outbreaks following introduction of virus, and allowing for vaccine effectiveness of 90%, coverage

needs to be even higher. Herd immunity can be thought of as a threshold level of immunity in the population above which measles no longer spreads, mathematically calculated from R0. As has been discussed, individual outbreaks are enormously informative but the collective wisdom gained from an analysis of the distribution of outbreak sizes and their duration (or generations of infection resulting over from each imported case) can provide a further measure of the robustness of elimination and the effective reproduction number, Re, which is the actual average number of secondary cases that result from an infectious case in a particular population. Re depends on the level of susceptibility in the population, in contrast to the basic reproduction number (R0), which is the average number of secondary cases arising from one infectious case in a totally susceptible population [33]. Well established methods exist to estimate Re from outbreak data and these have been applied in the United States, Canada and Australia [34], [35] and [36].