Safety and Immunogenicity of CoronaVac and ChAdOx1 Against the SARS-CoV-2 Circulating Variants of Concern (Alpha, Delta, Beta) in Thai Healthcare Workers
Authors: Angkasekwinai Nasikarn , Sewatanon Jaturong , Niyomnaitham Suvimol , Phumiamorn Supaporn , Sukapirom Kasama , Sapsutthipas Sompong , Sirijatuphat Rujipas , Wittawatmongkol Orasri , Senawong Sansnee , Mahasirimongkol Surakameth , Trisiriwanich Sakalin , Chokephaibulkit Kulkanya 
Published: October 2021

AbstractImportanceInactivated vaccine (CoronaVac) and chimpanzee adenovirus-vector vaccine (ChAdOx1) have been more available in resource-limited settings. However, the data comparing between these two vaccines in the same setting are limited.ObjectivesTo determine adverse events (AEs) and immunogenicity of CoronaVac and ChAdOx1 in health care workers (HCWs).DesignThis prospective study was conducted from February to July 2021.SettingA single center, university-based tertiary care center in Bangkok.ParticipantsHealthy HCWs.ExposureTwo doses of CoronaVac (4 weeks apart) or ChAdOx1 (8 weeks apart) intramuscularly.Main Outcomes and MeasuresSelf-reported AEs were collected for 7 days following each vaccination using electronic diary. The immunogenicity was determined by the level of IgG antibodies against receptor binding domain (RBD) of the SARS-CoV-2 spike protein (S1 subunit). The 50% plaque reduction neutralization tests against original Wuhan strain and circulating VOCs were performed in subset of samples at 2 weeks after the second dose.ResultsOf the 360 HCWs, 180 received each vaccine. The median (interquartile range: IQR) age was 35 (29-44) years old and 84.2% were female. Participants who received ChAdOx1 reported higher frequency of AEs than those received CoronaVac after both the first dose (84.4% vs. 66.1%, P < 0.001) and second dose (75.6% vs. 60.6%, P = 0.002), with more AEs in those younger than 30 years of age for both vaccines. The seroconversion rate was 75.6% and 100% following the first dose of CoronaVac and ChAdOx1, respectively. All participants seroconverted at 2 weeks after the second dose. The anti-SARS-CoV-2 RBD IgG levels induced by CoronaVac was lower than ChAdOX1 with geometric means of 164.4 and 278.5 BAU/mL, respectively (P = 0.0066). Both vaccines induced similar levels of neutralizing antibodies against the Wuhan strain, geometric mean titer (GMT) of 337.4 vs 331.2; however, CoronaVac induced significantly lower GMT against Alpha (23.1 vs. 92.5), Delta (21.2 vs. 69.7), and Beta (10.2 vs. 43.6) variants, respectively.Conclusions and RelevanceCoronaVac induces lower measurable antibodies but with lower frequency of AEs than ChAdOx1. The low neutralizing antibodies against the circulating VOCs induced by CoronaVac supports the need for earlier boosting to prevent breakthrough infections.Trial RegistrationTCTR20210720002 https://www.thaiclinicaltrials.org/QuestionWhat is the difference between CoronaVac and ChAdOx1 vaccines on safety and immunogenicity against the circulating variants of concern (VOCs) in the same setting?FindingsThis prospective study in 360 healthy health care workers reported higher frequency of adverse events following ChAdOx1 than CoronaVac particularly in those younger than 30 years old. The ChAdOx1 induced 3.3-4.3 times higher neutralising antibodies against VOCs than CoronaVac.MeaningThe 2-dose CoronaVac vaccination induced significantly lower level of neutralizing antibody against the circulating VOCs. An earlier booster may be needed to prevent breakthrough infection.