key: cord-0775746-0jo9ahvm
authors: Cucunawangsih, Cucunawangsih; Wijaya, Ratna Sari; Lugito, Nata Pratama Hardjo; Suriapranata, Ivet
title: Antibody response to the inactivated SARS-CoV-2 vaccine among healthcare workers, Indonesia
date: 2021-10-03
journal: Int J Infect Dis
DOI: 10.1016/j.ijid.2021.09.078
sha: 5ebe4a8584a1ae0ebde0508613582e61c25e23a4
doc_id: 775746
cord_uid: 0jo9ahvm

Background As healthcare workers (HCWs) are at high risk for SARS-CoV-2 infection, they have prioritized the COVID-19 vaccine. Inactivated SARS-CoV-2 vaccine has been mainly used in Indonesia to induce HCWs antibody response against SARS-CoV-2 infection. However, information regarding the kinetics of antibody-induced by this vaccine remains scarce. Objective To investigate the magnitude and durability of antibodies against spike (S) protein (anti-S) after complete dose of vaccination among HCWs by using the electrochemiluminescence immunoassay. Results Seroconversion of anti-S antibodies was observed among 159 (99.4%) of 160 HCWs after 14 days of full-dose vaccination. The levels of anti-S antibodies significantly decreased after day 42 compared to day 14 post-vaccination, but it persisted up to 98 days following vaccination. In contrast, the vaccinated HCWs with prior SARS-CoV-2 infection had significantly higher and stably elevated anti-S antibodies concentrations than vaccinated HCWs without SARS-CoV-2 infection history. Conclusion The remarkable decline and lower anti-S antibodies concentration among infection-naïve HCWs potentially indicate the additional booster dose of SARS-CoV-2 vaccination may be required to ascertain COVID-19 protection among HCWs by this vaccine. This early study of antibody response induced by inactivated SARS-CoV-2 vaccine among HCWs potentially contributes to the future policy decision regarding vaccination.

Healthcare workers (HCWs) are at risk for SARS-CoV-2 infection due to the increased occupational exposure to SARS-CoV-2 (Nguyen et al., 2020) . Protecting HCWs from SARS-CoV-2 infection would be beneficial for themselves and important for preventing disease transmission in healthcare and community setting (The Lancet, 2020). In addition, protecting

HCWs from COVID-19 is crucial for the preservation and protection nation's healthcare system (The Lancet, 2020). Therefore, HCWs are given priority for COVID-19 vaccination as soon as the first COVID-19 vaccine was approved and deployed in Indonesia (Ophinni et al., 2020) .

In that is likely more protective and long-lasting against SARS-CoV-2 infection (Abbasi, 2021) .

The presence of antibodies against RBD of the S protein, a critical region for interaction with host cell receptors, is important due to its capacity to block virus entry, thus preventing infection and transmission (Jeyanathan et al., 2020 ). In addition, the level of antibodies against RBD have been shown to correlate strongly with the level of protective neutralizing antibodies (Premkumar et al., 2020) . Therefore, the measurement of antibodies against RBD assay would be suitable for assessing natural or vaccine-induced immunity in a large-scale screening. However, further investigation will be necessary to determine whether this cut-off value of anti-S antibodies is applicable in predicting the protective antibody response postvaccination. Furthermore, compared to the anti-S antibodies level induced by the SARS-CoV-2 mRNA vaccine among healthy volunteers and measured by Elecsys anti-S immunoassay (Bradley et al., 2021) , the anti-S antibodies level induced by inactivated SARS-CoV-2 vaccine was lower, indicating the additional booster dose of SARS-CoV-2 vaccination may be required to ascertain COVID-19 protection among HCWs by this vaccine.

Overall, although we observed the detectable anti-S antibodies level among HCWs up to 98 days after the complete vaccination dose, the anti-S antibodies level was significantly lower than HCWs with prior infection. It is uncertain whether this anti-S antibodies level will be able to protect vaccinated HCWs against SARS-CoV-2 infection. Thus, further advanced techniques, such as plaque reduction neutralization test, are needed to establish the correlation between the protective anti-S antibodies level induced by inactivated SARS-CoV-2 vaccine with the overall adaptive humoral and cellular immunity. Moreover, although the molecular and serological criteria have been used to exclude previous SARS-CoV-2 exposure in our uninfected HCWs group, we cannot completely exclude the possibility that some of the HCWs in this group potentially had a previous undetected infection in early 2020, before molecular testing was conducted regularly at our hospital. The antibodies against nucleocapsid among undetected infection cases in the beginning pandemic possibly had waned below the detection level in our sampling baseline data; therefore, selection bias might have affected our findings. In the current situation where Indonesia faces a significant surge of active cases per day, and all HCWs in Indonesia were mainly vaccinated with inactivated 8 SARS-CoV-2 vaccine, this study provides valuable information regarding future policy decisions of HCWs vaccination programmes.

Titers of antibodies against RBD of the spike (S) protein (anti-S) among 160 healthcare workers (HCWs) without prior SARS-CoV-2 infection and 12 HCWs with prior SARS-CoV-2 infection was measured after 14, 42, 70, and 98 days post-vaccination. The black dotted line represents the positivity cut-off value of the Elecsys anti-SARS-CoV-2 S quantitative electrochemiluminescence immunoassay. Statistical analysis was performed via Mann-Whitney and Friedman test, *p<0.05, ** p<0.01, ****p<0.0001.

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The authors have declared no conflicts of interest.

No external funding was received.

This study was approved by the research ethics committee of Faculty Medicine of Pelita Harapan University (No: 137/K-LKJ/ETIK/IV/2021).

Designing research studies (CC, RW, NL), acquiring data (CC), analyzing data (CC, RW, NL, IS), interpreting the results (CC, RW, NL, IS), and writing the manuscript (CC, RW, NL, IS).