"In the MMR II group, 5 of 50 subjects had mumps titers of 182 AU/ml or above, and all 5 of these subjects... were functionally immune... Each had had several days of extensive exposure to an actively symptomatic person who was positive for SARS-CoV-2, e.g., a housemate or a spouse. These subjects took no social distancing or other precautions such as wearing masks. Despite this, the functionally immune subjects never tested positive for COVID-19 despite the ease of transmission of SARS-CoV-2."
--From the Gold MMR study recently published.
The total study was still fairly small, but the correlation between higher mumps titers and either immunity or very mild cases is clear. There's a massive study underway now get get more clarity on this, but since it's obvious that there is good likelihood of serious benefit, if not outright immunity to covid 19 and very little risk with a 50 year old vaccine, the reward:risk is compelling.
These findings do warrant a larger study. Any infection or vaccine triggers the immune system into higher gear. Hyperstimulation of the immune system can protect against infections or reduce their effects. The data they will look at will be whether this is a temporary protection or that the long-term immunity it confers for MMR also works for COVID.
The TB vaccine, BCG, also induces this kind of trained immunity and may be a reason for lower rates of COVID-19 in those countries that still give these vaccinations. The oral polio vaccine, OPV, has been found to have protections against heterologous infections and mortality. (Interesting related factoid: Infection with malaria parasites leads to a partial and short-term immunity that protects against a new infection.)
I read the MMR study and there was no information about the recency of the MMR vaccine, and, as you report, it was a very small pilot study with only 50 subjects. It would have very limited value if it works for very short periods of time or if it has a low efficacy level for COVID-19. It may take quite a while to get the findings from a good double-blind study.
It certainly makes sense to evaluate these and others for induction of a non-specific boost of immunity for COVID and could contribute to reducing the spread of infection in countries where there are limited supplies of the new vaccines. However, the new vaccines developed specifically for COVID-19 seem to have excellent efficacy and safety rates. It's possible that more serious problems for these vaccines can emerge over longer periods of time, but it does seem like our best bet by far at the moment.
OEXCHAOS, I'm wondering why you prefer the MMR to the Pfizer or Moderna vaccine.