Weak Cross-Lineage Neutralization by Anti SARS-CoV-2 Spike Antibodies after Natural Infection or Vaccination Is Rescued by Repeated Immunological Stimulation

Abstract

After over one year of evolution, through billions of infections in humans, SARS-CoV-2 has evolved into a score of slightly divergent lineages. A few different amino acids in the spike proteins of these lineages can hamper both natural immunity against reinfection, and vaccine efficacy. In this study, the in vitro neutralizing potency of sera from convalescent COVID-19 patients and vaccinated subjects was analyzed against six different SARS-CoV-2 lineages, including the latest B.1.617.2 (or Delta variant), in order to assess the cross-neutralization by anti-spike antibodies. After both single dose vaccination, or natural infection, the neutralizing activity was low and fully effective only against the original lineage, while a double dose or a single dose of vaccine, even one year after natural infection, boosted the cross-neutralizing activity against different lineages. Neither binding, nor the neutralizing activity of sera after vaccination, could predict vaccine failure, underlining the need for additional immunological markers. This study points at the importance of the anamnestic response and repeated vaccine stimulations to elicit a reasonable cross-lineage neutralizing antibody response.

Keywords: BAU; COVID; SARS; anamnestic response; neutralizing antibodies; vaccine; vaccine dose.

Figure 1

Neutralization activity of SARS-CoV-2 anti-spike antibodies from different groups of subjects against selected viral lineages. (a) Neutralization titers of vaccinees (n = 50) 2 weeks after the second dose of the BNT162b2 vaccine against 6 viral lineages. Three data points are outside the axis limits. Statistical difference was assessed by the Wilcoxon matched pairs signed rank test. (b) Neutralization titers of blood donors naturally infected by the B.1 lineage (n = 33) against 4 viral lineages. Statistical difference was assessed by the Wilcoxon matched pairs signed rank test. (c) Neutralization titers of blood donors naturally infected by the B.1.1.7 (white circles, n = 13), by P.1 (white triangles, n = 1), and B.1.351(white squares, n = 1) against 6 viral lineages. (d) Neutralization titers of subjects who became infected after a second dose of the BNT162b2 vaccine (vaccine failure, white circles, n = 12) compared to those from the general population of vaccinees (black circles, n = 50). Reductions in neutralizing titers were not statistically significant. Three data points are outside the axis limits. Statistical difference was assessed by the Mann-Whitney rank test. Neutralization titers <20 and >1280 were plotted, respectively, as 10 and 2560. Statistical significance: ns = p > 0.05, ** = p < 0.01, **** = p < 0.0001. Horizontal lines represent medians.

Figure 2

Antibody binding activity of sera from different groups of subjects. Antibody binding activity of: 50 naïve subjects vaccinated with a double dose of the BNT162b2 vaccine (BNT II: black circles); 12 subjects who became infected after a second dose of the BNT162b2 vaccine (BNT fail: white circles); 5 naïve subjects vaccinated with a double dose of AZD1222 (AZD II: black squares); 3 subjects vaccinated with a single dose of the BNT162b2 after natural infection (BNT I inf; black triangles); subjects vaccinated with a single dose of the AZD1222 vaccine after natural infection contracted between February and April 2020 (AZD I inf (Feb-Apr 20): white squares, n = 5), and between October to December 2020 (AZD I inf (Oct-Dec 20): white triangles, n = 5); subjects vaccinated with a double dose of the BNT162b2 vaccine after natural infection (BNT II inf: black diamonds n = 15), and the AZD1222 vaccine after natural infection (AZD II inf: white diamonds, n = 3). Values are expressed in binding antibody units (BAU/mL) according to the WHO standard. Horizontal lines represent medians.

Figure 3

Neutralization titers of sera from vaccinees with anamnestic response and immunological memory who had already experienced PCR-confirmed SARS-CoV-2 infection against different viral lineages. (a) Neutralization titers of subjects vaccinated with 2 doses of the BNT162b2 (black circles, n = 15), and the AZD1222 (white circles, n = 3), vaccines against 6 viral lineages of SARS-CoV-2. Horizontal lines represent medians. (b) Neutralization titers against 6 viral lineages of 9 subjects infected between February and April 2020 (black circles) compared to those of 9 subjects infected between October and December 2020 (white circles), both vaccinated with 2 doses of vaccine. Columns represent means, and error bars represent the standard deviation. Reductions of neutralizing titers were not statistically significant. (c) Neutralization titers against 6 viral lineages of 6 subjects infected between February and April 2020 (black circles), compared to 7 subjects infected between October-December 2020 (white circles), both vaccinated with 1 dose of vaccine. Columns represent means, and error bars represent the standard deviation. Reductions of neutralizing titers were not statistically significant. Statistical difference was assessed by the Mann-Whitney rank test. Neutralization titers <20 and >1280 were plotted as 10 and 2560, respectively.

Figure 4

Trend of neutralizing titers against different viral lineages in naive vaccinees and in vaccinees with previous SARS-CoV-2 after a single and a double dose of the respective vaccines. (a) Neutralization titers of 10 naïve subjects vaccinated with a single (black circles), and a double dose (white circles), of the BNT162b2 vaccine (b) Neutralization titers of 5 naïve subjects vaccinated with a single (black circles), and a double dose (white circles), of the AZD1222 vaccine (c) Neutralization titers of 3 subjects vaccinated with a single (black circles), and a double dose (white circles), with the BNT162b2 vaccine after natural infection (d) Neutralization titers of 3 subjects vaccinated with a single (black circles), and a double dose (white circles), of the AZD1222 vaccine after natural infection.