Substantial evidence indicates that the MMR II vaccine (known as MMRVaxPro in Europe) by Merck & Co. may inhibit development of SARS-CoV-2 infection or reduce COVID-19 severity. Our answers below are based upon early research, but nothing presented here should be relied upon to make medical decisions without consulting a physician or other qualified health professional.
Our findings are based on a correlation in retrospect, and have led to the development of a theory that is not yet proven by prospective testing. Unless and until positive results are obtained in prospective studies, where patients receive MMR II or not, and are followed for a significant period, the theory will not be fully tested. Further, a successful double-blind clinical trial will be needed to provide enough clinical evidence for general acceptance in the medical community (including insurance providers). No one should rely solely on MMR II for protection from COVID-19. They might use MMR II vaccination as a tool to support social distancing, wearing a mask, eating a well-balanced diet, getting proper exercise, and prudent behavior relative to crowded events where virus spread is common. It is our position that the use of MMR II should be supported by further clinical research. [LESS]
In our study we used Quest Diagnostics (Test Code 5259) for checking MMR titers including mumps. These same immunoassays may also be available from other labs. Specifications for these are detailed in the methods section of our titer paper. Different immunoassays may not result in titer levels correlating the same way they did in our study since each immunoassay measures titers differently.
MMR II (known as MMRVaxPro in Europe) is the only widely available MMR vaccine in the United States. It is manufactured by Merck and was initially licensed in 1979. It includes the Edmonston strain of measles, the Jeryl Lynn (B-level) strain of mumps, and the Wistar RA 27/3 strain of rubella. There are numerous variations in virus strains contained in MMR vaccines available in other countries. It is not known whether any of these other MMR vaccines produce mumps antibodies which may also be associated with COVID-19 severity.
Mumps antibodies from MMR II are exclusively from the Jeryl Lynn strain of mumps. Those born outside the United States, those born more than 42 years ago, or anyone who contracted mumps naturally as a disease may have antibodies from strains other than the Jeryl Lynn strain. Antibodies from natural disease did not correlate with COVID-19 severity in our study. This does not mean these other mumps antibodies are definitively not protective. It just means the mumps titer tests we used could not predict COVID-19 severity in those born in the U.S. over 42 years of age, those born in other countries where mumps may have been common as a natural disease, or in individuals who may have had other versions of the MMR vaccine.
While mumps titers were the only titers we found that significantly and inversely correlated with COVID-19 severity, this does not mean mumps antibodies are the only protective antibodies that result from MMR II vaccination. In fact it is possible that mumps titers are simply an accurate proxy measure of the general strength remaining of all antibodies from MMR II vaccinations, and that measles and/or rubella antibodies may be protective in addition to or instead of mumps antibodies. Even if measles or rubella antibodies are protective against COVID-19, this may not be able to be determined through simple titer tests. This is explained further in our current paper.
While the MMR II vaccine is very safe for the vast majority of people, there are circumstances when it should not be given. MMR vaccination safety should be discussed with a physician or other qualified health professional. Potential side effects and other information are available from the Centers for Disease Control and Prevention.
Regardless of any protection MMR II vaccination may offer against COVID-19, the MMR II vaccine works well to protect individuals from measles, mumps, and rubella infections. While rare in the United States there are still outbreaks of these diseases, and if someone travels to other countries with higher prevalence of these diseases the risk of exposure increases. Mumps antibodies are known to wane quickly after vaccination, and after a couple decades, an MMR II booster is important if for no other reason than to increase protection from mumps. In some cases a booster may also be needed to protect from measles and rubella. Preliminary evidence indicates it may be possible that MMR II may make some people functionally immune from COVID-19 for up to 9 years, after which it may still protect against severe COVID-19 disease in a manner which decreases over time. As such, if it has been over 9 years since someone was vaccinated with MMR II, it would be worth discussing with a medical professional whether one or two boosters may be warranted.
Those who have had past MMR II vaccinations may be sufficiently protected by a single MMR II vaccination, however, two MMR II vaccinations spaced at least 28 days apart will make it more likely that full protection is achieved rapidly.
We found in our study participants that Quest Diagnostics mumps titer levels ranging from 134 to 300 AU/ml in someone under age 42, who was born in the United States, meant they were either functionally immune to COVID-19 or had an asymptomatic case when infected with SARS-CoV-2. If someone was 42 or over, or was born outside the United States, their mumps titer levels were not predictive of how well protected they may be. If someone hasn't had an MMR II vaccination within the past few years and since high titers from past MMR illnesses do not necessarily indicate level of potential protection from MMR II, it would be be worth discussing with a medical professional whether one or two MMR II boosters may be warranted.
It is possible that antibodies from natural illnesses may sometimes be protective against COVID-19. There are, however, a variety of different strains of measles, mumps, and rubella, and all will cause someone to have high titer seropositivity for life, even if they are not protective against COVID-19. Those strains that may be protective will still have antibodies that wane after a period of years or decades. For these reasons, titers in people previously infected with natural diseases cannot be used to predict possible protection from COVID-19. As such, anyone who has high titers reflective of past illnesses, and who hasn't already had an MMR II vaccination within the past few years, should consider discussing with a medical professional whether one or two MMR II boosters would be appropriate.
Our research indicates that on average a series of two MMR II vaccinations may reduce the likelihood of an individual contracting COVID-19 for a period of 9 years, after which MMR II appears to continue to provide protection from severe disease for a number of additional years, possibly decades. Keep in mind, no vaccine is 100% effective and the time period over which antibodies wane varies from person to person.
Mumps titers in children decrease to a level that would no longer make them functionally immune to COVID-19 around age 14. This is on average 9 years after a child's second MMR II vaccination. Pediatricians may consider giving an additional MMR II booster if a child has not had one within the past 8 years, or if a Quest Diagnostics mumps IgG titer reveals a level below 134 AU/ml.