EFFICACY OF THE MEASLES-MUMPS-RUBELLA (MMR) VACCINE IN THE REDUCING THE SEVERITY OF COVID-19: AN INTERIM ANALYSIS OF A RANDOMISED CONTROLLED CLINICAL TRIAL

ABSTRACT Background COVID-19 is still a challenge, both with regard to its treatment and to the actual efficacy of the vaccines available to date, especially with the emergence of new variants. We evaluated the efficacy of the measles-mumps-rubella (MMR) vaccine in preventing SARS-CoV-2 infection and severity of COVID-19 in health workers. Methods This analysis includes data from one ongoing blinded, randomized, placebo-controlled trial with participants aged 18-60 years were randomly assigned to receive the MMR vaccine or a placebo. The primary efficacy analysis included all participants with a positive nasopharyngeal RT-PCR test since their inclusion. Results The MMR vaccine did not prevent the SARS-CoV-2 infection. Participants in the MMR group, compared with those in the placebo group, had a 48% risk reduction in symptomatic COVID-19 (RR = 0.52; 95% CI: 0.33–0.83; p=0.004) and a 76% risk reduction in COVID-19 treatment (RR = 0.24; 95% CI: 0.06 – 0.88; p = 0.020) with one dose and a 51% risk reduction in COVID-19 symptoms (RR = 0.49; 95% CI: 0.31 – 0.78; p = 0.001) and a 78% risk reduction in COVID-19 treatment (RR = 0.22; 95% CI: 0.06 – 0.82; p = 0.015) with two doses. Conclusions This interim analysis of an ongoing clinical trial suggests that compared with a placebo, the vaccine reduces the risk of COVID-19 symptoms and reduces the need for COVID-19 treatment. Clinical Trials Registry Brazilian Clinical Trials Registry (ReBEC n° RBR-2xd6dkj - https://ensaiosclinicos.gov.br/rg/RBR-2xd6dkj ). HIGHLIGHTS The MMR vaccine can stimulate the innate immunity inducing a nonspecific protection against other infections, called heterologous immunity. Repeated exposure to the antigen (innate immune response training) results in an extension of the action time of this immune response (innate immune response memory) and consequently in protection against other infections (heterologous immunity) for a longer time. The MMR vaccine has been used by national immunization programs in the world for many years, it is very safe and can be stored and distributed at 2-8°C, making it particularly suitable for global distribution. Among participants who received at least one dose, compared with those in the placebo group, participants in the MMR group had a significant risk reduction in symptomatic COVID-19 and of cases requiring treatment. The use of MMR vaccine can be useful in several populations in the world that do not have access to the COVID-19 vaccine and in a future epidemic or pandemic as an emergency measure until specific treatments or vaccines for each case are available to the general population.