Seroprevalence of immunoglobulin G antibodies against SARS-CoV-2 in Cyprus

Abstract

Monitoring the levels of IgG antibodies against the SARS-CoV-2 is important during the coronavirus disease 2019 (COVID-19) pandemic, to plan an adequate and evidence-based public health response. After this study we report that the plasma levels of IgG antibodies against SARS-CoV-2 spike protein were higher in individuals with evidence of prior infection who received at least one dose of either an mRNA-based vaccine (Comirnaty BNT162b2/Pfizer-BioNTech or Spikevax mRNA-1273/Moderna) or an adenoviral-based vaccine (Vaxzervia ChAdOx1 nCoV-19 /Oxford-Astra Zeneca) (n = 39) compared to i) unvaccinated individuals with evidence of prior infection with SARS-CoV-2 (n = 109) and ii) individuals without evidence of prior infection with SARS-CoV-2 who received one or two doses of one of the aforementioned vaccines (n = 342). Our analysis also revealed that regardless of the vaccine technology (mRNA-based and adenoviral vector-based) two doses achieved high anti- SARS-CoV-2 IgG responses. Our results indicate that vaccine-induced responses lead to higher levels of IgG antibodies compared to those produced following infection with the virus. Additionally, in agreement with previous studies, our results suggest that among individuals previously infected with SARS-CoV-2, even a single dose of a vaccine is adequate to elicit high levels of antibody response.

Fig 1. Anti-spike IgG antibody responses.

Anti-SARS-CoV-2 IgG levels were determined in individuals without or with evidence of prior infection. Participants were not vaccinated (UnVac) or received at least one dose of a vaccine against SARS-CoV-2 (Vac). The number of participants (n) in each group is shown in parentheses. Statistical significance was determined using the Kruskal Wallis test followed by Dunn’s multiple comparisons test. Horizontal bars indicate median values. Statistically significant differences are indicated with asterisks: ****p<0.0001. Dotted line: positive cut-off value.

Fig 2. Levels of IgG against SARS-CoV-2 in individuals without evidence of prior infection.

Participants received either one or two doses of a licensed vaccine. A) There were no significant differences in IgG in the three age groups. B) IgG levels according to vaccine type and the number of doses. Kruskal Wallis test followed by Dunn’s multiple comparisons test was used for statistical analysis. Statistically significant differences are indicated with asterisks: *p<0.05, ****p<0.0001, ns: non-significant. Horizontal bars indicate median values. Dotted lines: positive cut-off values.

Fig 3. Correlation of anti-SARS-CoV-2 IgG levels and age of participants without evidence of prior infection who had received at least one dose of a vaccine.

Correlation between IgG levels and the age of participants in three age groups namely 18–45 years (A), 46–65 years (B), and > 66years (C) was performed with Spearman’s r-test. Dotted lines: positive cut-off values.

Fig 4. Levels of anti-spike IgG across study groups.

Dot plots show the levels of anti-spike IgG in individuals without evidence of prior infection (NPI/V) who received one dose or two doses of a vaccine and unvaccinated individuals with evidence of prior infection (PI/U). The Mann-Whitney U-test was employed to compare the IgG levels in age groups. Statistically significant differences are indicated with asterisks: **p<0.01, ****p<0.0001, ns: non-significant. Horizontal bars indicate median values.

Fig 5. Anti-spike IgG levels by time in individuals who received a single dose of a licensed vaccine.

A) Regardless of the vaccine type. B) mRNA-based vaccine (Moderna or Pfizer/BioNTech). C) Adenoviral-based vaccine (Oxford-Astra Zeneca).

Fig 6. Anti-spike IgG levels by time in different groups.

A) No prior infection and received two doses of a licensed vaccine. B) Prior infection and received one dose or two doses of a licensed vaccine. C) Prior infection without vaccination. For those who received two doses of a vaccine, the plots depict IgG levels from the date of the first vaccination.