Participants gave oral permission for an interview and signed informed?consent?document for the use of their blood samples for serological studies regarding previous SARS-CoV-19 contamination serological responses to the Sputnik V vaccine. IgG antibody response against RBD after the first vaccine dose, with antibody levels 40% higher than seronegative individuals who had received 2 doses. Previously seropositive subjects showed no significant increase in IgG antibody response against RBD after the second vaccine dose. Conclusions: We demonstrate that 2 doses of the Sputnik V vaccine brought on antibody response in all study individuals. The second Sputnik V dose had no impact on IgG response for those seropositive for SARS-CoV-2 antigens before vaccination. Keywords: Sputnik V vaccine, IgG antibodies, receptor-binding domain name (RBD), nucleocapsid protein (NP), S/P ratio, vaccine booster dose Introduction Venezuela has authorized the use of the adenovirus-based vaccine Gam-COVID-Vac (Sputnik V) against COVID-19. Vaccination with Sputnik V relies on a heterologous prime-boost approach using 2 different adenovirus vectors (Logunov?et?al., 2021); people should get 2 doses, 3 weeks apart (Jones?et?al., 2021). Most other COVID-19 vaccines also require 2 doses, and current guidelines for COVID-19 vaccines assume that 2 doses are required to give full protection. However, in the light of a shortage in vaccine supplies and the Meptyldinocap high cost of vaccines, single-dose vaccination is an alternative strategy and a way to extend vaccine supply (Matrajt?et?al., 2021). Several studies have shown that people with previous exposure to SARS-CoV-2 tend to mount powerful immune responses to a single vaccine dose and gain little added benefit from the second dose. In Sweden, a single dose of the viral vector vaccine Oxford-AstraZeneca vaccine provided protection in previously infected recipients (Havervall?et?al., 2021). In the USA, based on serology testing, health care workers with previous COVID-19 infections had higher antibody titer responses after a single dose of the mRNA vaccine of Pfizer-BioNTech or the viral vector vaccine Moderna than those who had not been previously infected (Saadat?et?al., 2021, Krammer?et?al., 2021, Bradley?et?al., 2021. Ebinger?et?al., 2021). In Israel, it was found that individuals infected with SARS-CoV-2 pre-vaccination had a strong and persisting IgG response after one dose of the PfizerCBioNTech vaccine (BNT162b2). Dose 2 in those individuals had no impact on IgG responses (Jabal?et?al., 2021). In Argentina, individuals with anti-SARS-CoV-2 IgG responses at baseline showed significantly higher responses to the first dose of Sputnik V than people with no prior history of the disease (Chahla?et?al., 2021). In Italy, vaccination with BNT162b2 mRNA COVID-19 vaccine showed that in previously infected individuals, neutralizing antibody responses 7 days after the first vaccine dose were not significantly different from those observed in na?ve subjects 7 days after the second vaccine dose (Gobbi?et?al., 2021). In the UK, among participants who had received their first dose of the BNT162b2 mRNA COVID-19 vaccine, the vaccination increased anti-Spike responses at Meptyldinocap least one order of magnitude greater than what was reported following a conventional prime-boost vaccine strategy in previously uninfected individuals (Manisty?et?al., 2021). Furthermore, in India, a single dose of the COVISHIELD vaccine elicited the highest neutralizing antibody response and protective immunity among individuals who had been previously infected (Sasikala?et?al., 2021). Serology testing can help to determine whether vaccination results in the production of SARS-CoV-2 specific antibodies. Serology has been used to follow up on vaccination with several vaccines in various countries. Moreover, serology can provide us with data regarding the antibody response acquired from receiving a single versus double dose of the vaccine. Serological testing can also detect a PDGF-A previous COVID-19 contamination, irrespective of whether the individual had a severe or moderate illness or even asymptomatic contamination. COVID-19 vaccines do not induce antibodies to the virus nucleocapsid protein (NP) but induce antibodies against the receptor-binding domain name (RBD) of the spike protein. However, SARS-CoV-2 contamination induces IgG antibodies against RBD and NP (Assis?et?al., 2021). Here, we evaluated the IgG antibody response against the NP and the RBD of the spike protein of SARS-CoV-2 in 86 individuals just before, after the first, and after the second dose of the Sputnik V vaccine. The study was carried out on a cohort Meptyldinocap of hospital and laboratory workers, and serology differentiated this population into individuals with previous SARS-CoV-2 seroconversion and, according to their medical records, previously infected and SARS-CoV-2 antigen seronegative individuals with no previous history of SARS-CoV-2 contamination or disease. We decided if one dose of the Sputnik V vaccine could lead to seroconversion and established the benefits of a second vaccine dose. Material and methods Participants We randomly enrolled individuals who presented for vaccination (n=149) at a public hospital in Caracas, Venezuela. Before receiving the first dose of the Sputnik V vaccine, the participants were interviewed, and personal data, underlying illnesses and prior signs/symptoms or proof (reverse transcriptase-polymerase.