ABSTRACT
The course of the COVID-19 pandemic has been critically altered by the availability of vaccines. To assess the risk of COVID-19 in the vaccinated, as compared to the unvaccinated population, as well as the comparative effectiveness of the BBIBP-CorV (Sinopharm), BNT162b2 (Pfizer/BioNTech), Gam-COVID-Vac (Sputnik V) and ChAdOx1 (AstraZeneca) vaccines in the prevention of clinical infection, we carried out a retrospective study of the incidence of clinical COVID-19 in the Belgrade city municipality of Vozdovac among both vaccinated and unvaccinated individuals during a 4-month period between 1 July and 31 October 2021. The study included all individuals with a symptomatic infection confirmed by a positive PCR and/or antigen test. Only those who received two vaccine doses were considered as vaccinated. The results showed that of the Vozdovac population of 169,567, a total of 81,447 (48%) individuals were vaccinated by the end of the study. Vaccination coverage increased with age, ranging from 1.06% in those below age 18, to even 78.8% in those above 65 years of age. More than one half (57.5%) of all those vaccinated received BBIBP-CorV, while 25.2% received BNT162b2, 11.7% Gam-COVID-Vac and 5.6% ChAdOx1. The overall risk of infection of the vaccinated vs. the unvaccinated was 0.53 (95% CI 0.45-0.61). Compared to the incidence of COVID-19 of 8.05 per 1000 in the unvaccinated population, the relative risk in the vaccinated was 0.35 (95% CI 0.3-0.41). The overall VE was 65%, differing widely among age groups and by vaccine. VE was 79% for BNT162b2, 62% for BBIBP-CorV, 60% for ChAdOx1 and 54% for Gam-COVID-Vac. The VE for BBIBP-CorV and BNT162b2 increased with age. The obtained results demonstrate a significant overall effectiveness of anti-COVID-19 vaccination, which, however, varied significantly among the analyzed vaccines, and was the highest for BNT162b2.
ABSTRACT
Older people in nursing homes (NH) have been hit particularly hard by the COVID-19 pandemic. We conducted a retrospective study of three outbreaks of COVID-19, occurring during the waves of the initial pre-Alpha, Delta and Omicron SARS-CoV-2 variants, in one NH in suburban Belgrade, Serbia. All staff and 95% residents were vaccinated in February 2021, mostly with BBIBP-CorV, and two thirds were boosted with a third dose in August 2021. COVID-19 was diagnosed by positive PCR and/or antigen test. After the first outbreak, 80 affected individuals were tested for SARS-CoV-2 specific antibodies. The first outbreak involved 64/126 (50.8%) residents and 45/64 (70.3%) staff, the second 22/75 (29.3%) residents and 3/40 (7.5%) staff, and the third involved 36/110 (32.7%) residents and 19/56 (33.9%) staff. Clinical presentation ranged from asymptomatic to severe, with severe cases referred to hospital ICUs. Deaths occurred only in residents, and the case fatality rate was 31.2%, 9.1% and 0%, respectively in outbreaks 1, 2 and 3. Specific IgG antibodies were detected in all 35 residents and 44 of the 45 staff, and higher IgG levels were detected in the residents (417.3±273.5) than in the staff (201.9±192.9, p<0.0001) despite a double difference in age (79.0±7.4 vs. 40.1±11.5 years). Outbreaks 2 and 3 involved four and 23 breakthrough infections, respectively. Older individuals mounted a good immunological response to SARS-CoV-2 infection and vaccination, which prevented significant mortality and severe morbidity in the subsequent outbreaks, despite a significant number of breakthrough infections.
ABSTRACT
Real-life data on the performance of vaccines against SARS-CoV-2 are still limited. We here present the rates of detection and levels of antibodies specific for the SARS-CoV-2 spike protein RBD (receptor binding domain) elicited by four vaccines available in Serbia, including BNT-162b2 (BioNTech/Pfizer), BBIBP-CorV (Sinopharm), Gam-COVID-Vac (Gamaleya Research Institute) and ChAdOx1-S (AstraZeneca), compared with those after documented COVID-19, at 6 weeks and 3 months post first vaccine dose or post-infection. Six weeks post first vaccine dose, specific IgG antibodies were detected in 100% of individuals fully vaccinated with BNT-162b2 (n = 100) and Gam-COVID-Vac (n = 12) and in 81.7% of BBIBP-CorV recipients (n = 148), while one dose of ChAdOx1-S (n = 24) induced specific antibodies in 75%. Antibody levels elicited by BNT-162b2 were higher, while those elicited by BBIBP-CorV were lower, than after SARS-CoV-2 infection. By 3 months post-vaccination, antibody levels decreased but remained ≥20-fold above the cut-off in BNT-162b2 but not in BBIBP-CorV recipients, when an additional 30% were seronegative. For all vaccines, antibody levels were higher in individuals with past COVID-19 than in naïve individuals. A total of twelve new infections occurred within the first 3 months post-vaccination, eight after the first dose of BNT-162b2 and ChAdOx1-S (one each) and BBIBP-CorV (six), and four after full vaccination with BBIBP-CorV, but none required hospitalization.