SARS-CoV-2 IgG Antibody Levels After Inactivated Vaccine (CoronaVac) among Elderly (2024)

Abstract

We aimed to describe the antibody response against SARS-CoV-2 after inactivated COVID-19vaccine in elderly individuals. SARS-CoV-2 IgG levels were measured in the blood samplesof 126 volunteers over the age of 60. The antibody positivity rate was 42.8% after thefirst dose and 96.8% after the second dose of the vaccine. The median antibody titersafter two vaccine doses were 561.3AU/mL and 43AU/mL, respectively(p<0.001).After vaccination, 22.2% of the participants had antibodies equivalent to 1:80 dilutionsin plaque reduction neutralization test (PNRT). We believe that the booster dose is neededto continue the protective immune response in especially elderly groups.

Keywords: COVID-19, SARS-CoV-2, inactivated vaccine, CoronaVac, antibody

Introduction

Despite the decrease in incidence after having widespread vaccination programs, theCOVID-19 pandemic continues to cause high morbidity and mortality in the world in its secondyear (1). Especially elderly people (over 65 yearsold), people with underlying health conditions, and healthcare workers (HCWs) are still athigh risk for COVID-19 disease (2). Since there isno specific treatment against SARS-CoV-2 infection, the most effective way to preventinfection is to gain immunity with an effective vaccine.

CoronaVac (Sinovac Life Sciences, Beijing, China), an inactive vaccine, is the firstvaccine administered in our country. In a phase 2 study, the seroconversion rate at day 28after CoronaVac was reported 90.7% in the 1.5 µg group, 98% in the 3-µg group, and 99% inthe 6-µg group (3). We aimed to describe theSARS-CoV-2 IgG response in blood samples taken 28 days after the first dose and 28 daysafter the second dose from the individuals aged between 60 and 90 years who applied to ourvaccine center for the administration of SARS-CoV-2 inactivated vaccine.

Materials And Methods

The 156 volunteers aged 60-90 years, who received the first dose of CoronaVac (Sinovac LifeSciences, Beijing, China) vaccine between January 14, 2021, and February 22, 2021, and thesecond dose of CoronaVac vaccine between February 11, 2021, and March 22, 2021, wereincluded. At various stages, 30 volunteers left the study voluntarily. It was planned tocollect peripheral blood samples from the participants 28 days after the first dose (i.e.,before the second dose) and 28 days after the second dose to determine the SARS-CoV-2 IgGlevels. Demographic information of all participants (age, gender, history of COVID-19,presence of comorbidities, etc.) was recorded in the follow-up form. A chemiluminescentmicroparticle immunoassay (CMIA)-based test (ARCHITECT IgG II Quant test, Abbott, USA) thatquantitatively detects IgG antibodies specific to the RBD (receptor binding domain)/S1region was used in the analysis of blood samples. The results obtained from all seraincluded in the study were evaluated as arbitrary unit/mL (AU/mL). The concentrationsobtained as AU/mL were converted into the World Health Organization's (WHO) internationalstandard for anti-SARS-CoV-2 immunoglobulin “binding antibody unit (BAU/mL)” by multiplyingwith the correlation coefficient of 0.142 (4).According to this, concentrations of 50 AU/mL or 7.1 BAU/mL and above were consideredpositive. In addition, a concentration of 1050 AU/mL, which was reported to be 100%compatible with the plaque reduction neutralization test (PRNT), was associated with a 1:80dilution of PRNT (5).

Statistical Analysis

The Statistical Package for Social Sciences (SPSS) version 21.0 (IBM Corp., USA) was usedfor analysis. Qualitative data were presented as numbers and percentages, and quantitativedata as mean and standard deviation. Chi-square test and Fisher's exact test were used inthe evaluation of qualitative data, Student's test, Mann Whitney U test, and Kruskal Wallistest were used in the comparison of quantitative data, Spearman analysis was used incorrelation analysis. The p<0.05 was considered as statisticalsignificance.

Results

Of the 126 participants included in the study, 66 (52.4%) were female, 60 (47.6%) weremale, mean age was 69.43±5.4 (minimum 60, maximum 90 years). While no comorbidity was foundin 45 (35.7%) of the participants, there were at least one comorbidity in 81 (64.3%)participants. None of the participants had a prior history of COVID-19. The antibodypositivity rate was 42.8% 28 days after the first dose of vaccine, and 96.8% after 28 daysafter the second dose of vaccine. Four participants did not develop an antibody response (Table 1). The mean age of these patients is 72.5, and two ofthem had hypertension.

After two doses of vaccination, 22.2% of the participants had antibodies above 1050 AU/mLtiter, which is equivalent to 1:80 dilutions in the plaque reduction neutralization test.Antibody response was not statistically significant between genders. While the medianantibody titer of the participants was 43 AU/mL (Interquartile range [IQR]%:17.2-101.6)after the first dose of the vaccine, a statistically significant increase was observed afterthe second dose, with 561.3 AU/mL (IQR%:270.8-979.2) (p<0.001). When theantibody titers after the first and second dose were evaluated in terms of the presence ofcomorbidity, no significant difference was found.

Discussion

It was determined that 96.8% of the elderly individuals participating in our studydeveloped Anti-SARS-CoV-2 IgG positivity with two doses of inactivated vaccine, butneutralizing antibody titer equivalent to 1/80 PRNT level was detected only in 22.2%.

When Karameşe et al. (6) examined the antibodytiters with QuantiVac anti-SARS-CoV-2 enzyme-linked immunosorbent assay (ELISA) (IgG)(Euroimmun AG, Lubeck, Germany) in their study with 235 people aged 65 and over who wereadministered CoronaVac vaccine, they found the antibody titers to be 37.70 ± 57.08 IU/mLafter the first dose, and 194.61 ± 174.88 IU/mL after the second dose. When they examinedthose below the 25.6 IU/mL value determined as negative by WHO in the same study; statedthat they found this rate to be 57.02% after the first dose and 11.48% after the seconddose. They stated that 120 of the 235 people included in the study had at least one comorbidcondition and that the effect of diabetes mellitus (DM) on the antibody level wasstatistically significant (6). Our findings weresimilar to findings of the report by Karameşe et al., although they detected a statisticalcorrelation between DM and antibody level only among comorbidities, no such correlation wasfound in our study. This may be due to the lower number of patients with DM in our study.

Our knowledge about vaccines is that the response would be lower among obese people, bothin case of vaccination and exposure to infections (7).However, regarding SARS-CoV-2, the vaccine efficacy data of three FDA-approved SARS-CoV-2vaccines (Pfizer-BioNTech, Moderna, and Johnson & Johnson) in obese and non-obeseindividuals in multicenter and large-participation studies did not report the difference (8). Malavazos et al. (7) found that abdominal obese individuals without a history ofCOVID-19 and vaccinated with BNT162b2 mRNA vaccines (Pfizer-BioNTech) produced a lowerantibody response, however overweight individuals produced higher antibody titers, similarto our results after the first vaccination. However, no statistically significant resultswere obtained between non-obese individuals and obese individuals who were vaccinated withthe CoronaVac.

In the study of Seyahi et al. (9), when theydetected the antibody levels after the 2nd dose using the Elecsys kit in 47 people aged 65and over, whom they included in the study as a control group, they reported that 14.9% ofthese individuals have a high antibody titer above 250 U/mL, a moderate antibody titer inthe range of 117-250 U/mL in 19.1%, and a low antibody titer below 117 U/mL in 66% of thestudy population. In another study conducted among 24 HCWs over 60 years of age without aprior history of COVID-19 infection, an antibody response at the level of 38.2 AU/mL wasdetected in 9 (37.5%) of the participants 28 days after the CoronaVac vaccine. In the samestudy, 21 days after the second dose, they reported that 22 (95.7%) of them produced anantibody response at the level of 733.5 AU/mL (10).The findings of these reports were similar to the results of our study.

The lack of the pre-vaccine antibody titers was one of the limitations of our study. On theother hand, our study is important in terms of comorbidity, equal distribution betweengroups in terms of gender and BMI, the absence of a history of COVID-19 infection of theparticipants, and the antibody response levels to the vaccine in elderly people who werevaccinated with inactive SARS-CoV-2 vaccine for two doses.

The findings of our study reveal that neutralizing antibody levels are relatively low inelderly individuals. Within the framework of these findings, it is recommended that thethird dose of vaccine is needed for the continuation of the protective immune response inelderly individuals, to prevent infection.

Acknowledgements

The authors would like to thank Songül Gedik Koç, Feray Ergen, Yasemin Öztürk, ElfideŞentürk Yurdatapan, Demet Durgun Karakaş, Nafiye Güder and Fatih Hekimoğlu for thiercontributions the paper.

Additional Information

References