No, that's not correct. What has happened is that before the vaccine, children rarely got measles before 18 months because maternal antibodies were very high as a result of good solid natural immunity. Now, maternal antibodies are so low from a vaccine that simply doesn't prime the immune system like natural infection does, that babies are at risk of getting getting measles at a younger and younger age, because maternal antibodies no longer last 15 - 18 months.
The problem with that is that the peripheral blood leukocytes of babies have an enhanced susceptibility to measles virus http://www.ncbi.nlm.nih.gov/entrez/q...=pubmed_docsum
at an age when naturally, they shouldn't be coming in contact with measles at all.
So if there is even the slightest nutritional or immunological problem these babies are at increased danger from the ordinary same old measles virus, because of the difference between the immune system of a baby and a toddler.