Was the MMR Vaccine Tested With a Placebo?

Was the MMR vaccine tested with a placebo before it was approved? This page documents the pre-licensure clinical trial evidence for M-M-R II — including Merck's trial design and the controls used.

Clinical trial data for the two MMR vaccines on the US childhood schedule. MMR-II (Merck, 1978) was licensed with no control group, in a trial of 834 children, monitored for 42 days. About one-third of trial participants developed gastrointestinal issues and one-third developed respiratory issues — with no control group, these rates could not be compared to a baseline. Priorix (GSK, 2022) was licensed against MMR-II — and its 6-month monitoring window revealed a 10.1% emergency room visit rate and a 3.4% new chronic disease rate in vaccinated children. These findings were not disclosed in the package insert; they appear only in a supplemental table of a journal article.

MMR-II (Merck)

FieldValue
Licensed1978
Trial population834 children
Control groupNone
Safety monitoring window42 days

Source: FDA-approved package insert; Merck licensure submission.

Trial Findings (No Control Group)

During the 834-child trial:

Because there was no control group, it is impossible to determine whether these rates were elevated compared to background illness in unvaccinated children. The FDA licensed the product without requiring a comparison.

Aborted Fetal Cell Line DNA

Every vial of MMR-II contains, according to evidence conceded by Stanley Plotkin during his 2018 deposition, hundreds of billions of pieces of human DNA and cellular material derived from a continuously cultured cell line originating from an electively aborted fetus. This is disclosed in the package insert but not routinely communicated to parents. See Plotkin Deposition 2018.

Priorix / MMR-RIT (GSK)

FieldValue
Licensed2022
Trial populationMMR-RIT: N=3,714
Control groupMMR-II (N=1,289)
Safety monitoring window6 months

Source: FDA-approved package insert; GSK clinical trial supplemental publications.

Trial Results — Buried in Supplemental Journal Table

The serious harm rates from the Priorix trial were not disclosed in the package insert that physicians and parents read. They were published only in a supplemental table of a peer-reviewed journal article, accessible to researchers who located and read the supplemental materials.

MetricMMR-RIT (N=3,714)MMR-II (N=1,289)
Any unsolicited adverse event50.0%47.9%
Grade 3 unsolicited AEs6.1%6.6%
Serious adverse events (SAEs)2.1%1.9%
AEs prompting ER visit10.1%10.4%
New onset chronic diseases (NOCDs)3.4%3.7%

New Onset Chronic Diseases Recorded

NOCDs documented within 6 months of vaccination included:

What These Numbers Mean

Hidden from the Package Insert

These rates do not appear in the package insert that pediatricians consult before administering Priorix. A physician relying on the package insert would not know that 1 in 10 children went to the ER within 6 months of receiving the vaccine in the trial.

Summary Table

BrandLicensedControlTrial SizeWindowER Visit RateNOCD Rate
MMR-II (Merck)1978None83442 daysNot measuredNot measured
Priorix (GSK)2022MMR-II3,714 / 1,2896 months10.1%3.4%

Pyramid Position

Priorix → MMR-II (no control, 834 children, 42 days) → no baseline. Two levels of "as safe as" comparisons, with the foundation being a 1978 trial that had no control group at all.

Schedule

DoseTiming
Dose 112–15 months
Dose 2 (booster)4–6 years

Disease Context

Measles, mumps, and rubella are three viral diseases targeted by the combination vaccine. Measles caused significant childhood mortality and morbidity before vaccine introduction (~450 US deaths per year pre-vaccine). Mumps causes parotitis and rare complications including orchitis and meningitis. Rubella is a mild illness in children but causes congenital rubella syndrome when contracted in early pregnancy.

See Also

MMR Vaccines (Post-Licensure), Pre-Licensure Safety Testing, Plotkin Deposition 2018, Stanley Plotkin, Childhood Vaccine Schedule, Varicella Vaccines (Pre-Licensure), Combination Vaccines (Pre-Licensure), Kathryn Edwards, 1986 Act (National Childhood Vaccine Injury Act), Henry Ford Vaccinated vs. Unvaccinated Study, Merck, GSK

Frequently Asked Questions

Frequently Asked Questions

Was the MMR vaccine tested with a placebo before approval?
No. MMR-II (Merck, 1978) was licensed with no control group at all. The trial enrolled only 834 children and monitored them for 42 days. Without a control group, the high rates of gastrointestinal and respiratory issues observed in participants (approximately one-third for each) could not be compared to any baseline. This is documented in the FDA-approved package insert.
How many children were in the original MMR clinical trial?
The MMR-II pre-licensure trial enrolled 834 children with no control group and a 42-day monitoring window. This is the entire safety basis for a vaccine given to millions of children annually. A trial of this size cannot detect adverse events occurring at rates lower than approximately 1 in 200, and the absence of a control group means even observed events cannot be attributed to the vaccine. These details come from Merck's FDA-approved package insert.
What does the 10.1% ER visit rate in the Priorix trial mean?
In the Priorix (GSK, 2022) clinical trial, 10.1% of children who received Priorix and 10.4% who received MMR-II visited an emergency room within 6 months of vaccination. This means more than 1 in 10 children in both groups required emergency care. These rates were not disclosed in the package insert — they appeared only in a supplemental table of a peer-reviewed journal article that most physicians would never read.
What new chronic diseases were found in the MMR clinical trial?
The Priorix trial documented a 3.4% new onset chronic disease rate within 6 months of vaccination — meaning more than 1 in 30 children developed a new chronic condition. These included autoimmune disorders, asthma, type I diabetes, vasculitis, celiac disease, thrombocytopenic purpura, and allergies. Because the MMR-II control group showed similar rates (3.7%), the FDA deemed both products equivalently safe — but neither was compared to an unvaccinated group.
Does the MMR vaccine contain aborted fetal cell line DNA?
Yes. Every vial of MMR-II contains hundreds of billions of pieces of human DNA and cellular material derived from a continuously cultured cell line originating from an electively aborted fetus. This was conceded by Stanley Plotkin during his 2018 deposition under oath. The fetal cell line origin is disclosed in the package insert but is not routinely communicated to parents before vaccination.

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