Humoral immunoresponse elicited against an adenoviral-based SARS-CoV-2 coronavirus vaccine in elderly patients

Abstract

The early sequencing of the SARS-CoV-2 viral genome allowed for a speedy development of effective vaccines against the virus. Nevertheless, age-related immunosenescence, the inability to mount strong immune responses, still represents a major obstacle. Here, in a group of 149 elderly volunteers (70-96 years old), evolution of the humoral immune response over time to Gam-COVID-Vac (Sputnik V), a vaccine based on heterologous recombinant adenovirus-26 (Ad26) and adenovirus-5 (Ad5) carrying the Spike genome, was analyzed by an anti-RBD ELISA. At 28 days post vaccination (dpv), a seroconversion rate of 91% was achieved, showing the importance of administering at least two doses of Gam-COVID-Vac to elicit a robust immune response, especially in elderly individuals without previous SARS-CoV-2 infection. Interestingly, IgG specific antibodies that reached their highest titers around 28 dpv (median = 740), persisted without significant decrease after 60 dpv (median = 650). After 90 dpv, IgG titers began to drop, and at 180 dpv only 44.7% of the elderly individuals remained with detectable anti-RBD IgG antibodies. No significant differences were observed in specific humoral immune responses between genders at early times point. However, at 60 dpv anti-RBD titers were more persistent in elderly females, and only dropped at 90 dpv (p < 0.0001). As expected, the highest antibodies titers were elicited in the youngest subgroup (70-74 years). Our results show that Gam-COVID-Vac was able to deal with the ageing of the immune system, eliciting a robust immune response in an elderly cohort, which lasted approximately 90 dpv at high levels, and protected against COVID-19.

Keywords: COVID-19; Gam-COVID-Vac; SARS-CoV-2; elderly; humoral immune response.

Figure 1

Humoral immune response to the Gam-COVID-Vac in 149 elderly individuals. (A) A cross-sectional study of IgG anti-RBD titers measured by ELISA in serum samples taken at 0, 14, 28, 60, 90 and 180 days’ post-vaccination (dpv). CP: SARS-CoV-2 Convalescent plasm (n = 309) analyzed with the same ELISA platform [17]. Statistical analyses were performed with Kruskal-Wallis test with two-stage linear step-up procedure of Benjamini, Krieger and Yekutieli. ^***p < 0.0001; ^*p < 0.05 and ns = not-significant. (B) Percentage of anti-RBD seropositive responses to the Gam-COVID-Vac vaccine in the population studied.

Figure 2

Anti-RBD titers elicited in individuals with or without positives serology at baseline. Antibodies titers in the studied population grouped according to documented absence or presence of previous SARS-CoV-2 infection (defined by positive RT-qPCR, rapid antigen test, or basal anti-RBD titer). Horizontal red lines represent the median. Statistical analyses were performed with Mann-Withney test.

Figure 3

Distribution of IgG anti-RBD titers measured up to 180 dpv differentiated by gender groups. (A) Specific SARS-CoV-2 anti-RBD antibody titers were analyzed according to male or female gender groups, before and at different times post-vaccination (0, 14, 28, 60, 90 and 180 dpv) by ELISA. Horizontal red lines represent the median. Statistical analyses were performed with Mann-Withney test. ^*p < 0.05. (B) Seroconversion of IgG anti-RBD among the time post-vaccination in female and male groups.

Figure 4

Anti-SARS-CoV-2 humoral immune responses in different age subgroups. Serum IgG anti-RBD of the SARS-CoV-2 were determined at several times post Gam-COVID-Vac in individuals classified into the following age subgroups: 70-74, 75-79, 80-84 and 85-96 years old. Horizontal red lines represent the median.