In a prospective observational trial we followed MMR vaccinated subjects searching for COVID-19 cases (ethics committee: CONBIOÉTICA-09-CEI-018-20160729). All patients were vaccinated subcutaneously with 0.5mL of the MMR vaccine containing live-attenuated virus (≥1,000 CCID50 of measles, ≥5000 CCID50 of mumps and ≥1000 CCID50 of Rubella virus) and follow-up was given by (bi)monthly phone calls or contact via electronic media. COVID-19 infection was considered confirmed with a positive result of the SARS-CoV-2 reverse transcription polymerase chain reaction (RT-PCR), the detection of SARS-CoV-2 specific antibodies or the combined presence of a direct contact with a confirmed case plus anosmia/ageusia plus at least two classic symptoms. Direct contact with a confirmed case, accompanied by classic symptoms, but without olfactory nor gustatory alterations were considered highly probable cases. We graded the clinical severity of COVID-19 on a simplified scale we considered more suitable in an out-patient setting, see table 1.
Among the 255 vaccinated subjects there are 24 confirmed and 12 (highly) probable COVID-19 cases, thirteen of them with hypertension, diabetes, obesity, smoker or uncontrolled asthma as possible risk-factors. As people are generally very reluctant to go to a laboratory or take a chest X-ray, we have installed close follow-up in probable positive cases with pulse oximetry and home peak-expiratory-flow rate (PEF) measurements. All received general supportive measures and the policy toward fever was permissive, keeping paracetamol use to a minimum. Some received off-label high-dose ivermectin the first two days. All had minor respiratory symptoms at most; only one uncontrolled asthmatic had one day hypoxemia. None presented respiratory insufficiency to the degree of needing oxygen.
Table 1 (scroll to the right, total 12 columns). Cases of COVID (confirmed or highly probable) within weeks of
MMR vaccination, COVID severity compared with case fatality rates for
Mexico per age-sex group and per co-morbidity.