Determining the extent of immunity induced by booster doses of COVID-19 vaccinations is crucial for informing recommendations for booster dose regimens as well as constant adjustments of immunization strategies amongst different groups of people within the population. The study involved 31 healthy volunteers (majority were healthcare professionals) who completed either vaccination course with Pfizer or Moderna mRNA vaccines and received a third dose of the vaccine. Here we report results on the evaluation of an antibody response to four different SARS-CoV-2 antigens: RBD, S1, S2 and nucleocapsid prior to third dose and two and four weeks after a booster vaccination. We detected a peak of high titers of antibodies after the third dose with a gradual decline after four weeks. No significant differences were seen between the two vaccines in terms of antibody response. There were no gender discrepancies between the two vaccines. Our results suggest that: third doses are necessary due to the emergence of different SARS-CoV-2 variants and postvaccination antibody testing continues be essential in determining possible standardization of SARS-CoV-2 vaccines regimens.