Can children receiving MMR vaccine become a source of contagion?
After being vaccinated against measles, rubella and mumps, the child does not pass these viruses on to the people they come in contact with.
The live attenuated virus contained in vaccines retains the characteristics of the original virus but is rendered "weak", that is, it is deprived of the aggressiveness of the natural virus. In this way, the vaccine virus, after its administration, mimics an infection without disturbances (symptoms) or very light, allowing the child to develop antibodies and, therefore, is protected from the disease which, if caused by the natural virus, could be very aggressive. .
A vaccine prepared with live attenuated viruses is that against measles, mumps and rubella (MMR vaccine).
Scientific studies have shown that, approximately 7-28 days after vaccination, some children may have rubella or measles virus in their throats. This data can be alarming and has been misused to claim that vaccinated children can be a source of contagion. This is not true; the live attenuated virus must replicate in the child to stimulate an immune response but there is no scientific evidence that it has "the strength" to pass on to others. In decades of study, not a single case of human-to-human infection by the viruses contained in the MMR vaccine has been reported. The child vaccinated with MMR is therefore not a source of contagion, neither immediately after vaccination nor a few weeks later. The only certain fact is that infections caused by natural viruses are very contagious and much more aggressive: the probability of encephalitis as an adverse event after measles vaccination is in the order of one case in three million doses; that of developing encephalitis following a natural measles infection is 1 in 1000 cases.
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