In the context of the ongoing COVID-19 pandemic, using a half-dose schedule vaccination can help to return to normalcy in a cost-efficient manner, which is especially important for low and middle-income countries. We undertook a study to confirm that in adults up to 55 years old, the humoral response to the half-dose (15 µg, 35 participants between 18 and 55 years old) and to the recommended dose (30 µg, 155 participants) in the two-dose three-week interval schedule would be comparable. Antibody levels were measured by the Elecsys Anti-SARS-CoV-2 S assay (Roche Diagnostics, upper detection limit: 2570 BAU/mL) on the day of dose 2 of the vaccine and then 8-10 days later to assess peak response to dose 2. The difference in proportions between the participants who did and did not exceed the upper detection limit 8-10 days after dose 2 was not statistically significant (p = 0.152). We suggest that a half-dose schedule can help to achieve widespread vaccination coverage more quickly and cheaply.
Keywords: COVID-19; SARS-CoV-2; mRNA vaccine.