A recent article in Science authored by Michael Mina and colleagues concludes that measles infection reduces antibodies that provide protection against infections thereby reducing the benefits of prior vaccination (https://science.sciencemag.org/content/366/6465/599).
Measles vaccination acts as an essential complement to other vaccines; hence, defining system strength by DTP3 or MCV1 coverage appears inadequate. Because coverage can also be seen as a probability, it is possible to multiply DTP3 and MCV1 coverage to obtain the probability that an infant has received both. With this joint coverage approach, there is still a reassuringly high number of countries where coverage exceeds 90%. However, not surprisingly, there are about twice as many countries with coverage less than 70% using the joint methodology than through the use of either DTP3 or MCV1.
The use of a joint coverage approach may be better at identifying weaknesses and fragility in immunization systems.