Does contracting Rubella give one some kind of immunity to Measles and vice versa?

Question

Both these diseases- Measles and Rubella, have very similar symptoms, have similar complications and are often confused for one another. And both the diseases have a common MMR vaccine. So, are the culprit viruses also related, so that contracting one can give one at least partial immunity to the other as well?

The similarity in symptoms is striking. Both the diseases may start with cold and fever. Both give one rashes, that start from face, and spread to rest of the body. Both have similar complications associated with them like brain infection. In the end, both can cause miscarriage, preterm birth, or stillbirth, as well as a variety of birth defects in pregnant women.

I know from this source that lab tests exist which can tell whether a person has immunity to one of the MMR diseases (Measles, mumps and rubella) and not the other, implying that there is a possibility of immunity to one and not the other. But since the vaccines like MMR only ensure immunity for 99% people who get the shot, my question is- does there exist partial immunity (in some people and not others, or in less severe attack and not otherwise) to Rubella if one has contracted Measles before and vice versa?

Answer 1

Short answer: No, there is no cross immunity between these two diseases. Having the same symptoms doesn't mean that diseases are related.

Both have in common that they are caused by viruses, but similarities end here. Rubella is caused by the rubella virus, which is the only member of the genus Rubivirus and belongs to the family of Togaviridae and are encapsulated positive strand RNA viruses.

Measles on the other hand are caused by the measles virus, which belong to the genus Morbillivirus within the family Paramyxoviridae and are negative stranded enveloped RNA viruses.

Historically speaking, the measles vaccine was available first in 1963, with mumps following in 1967 and rubella in 1969. All three are attenuated live vaccines which have been combined into a single vaccine in 1971. The sequence of this developments also shows that there is no cross immunity. You wouldn't develop another vaccine, when the disease is already covered by another. Drug development is a very expensive business.