key: cord-0691992-pj9p07vo
authors: Yavuz, Erdinç; Günal, Özgür; Başbulut, Eşe; Şen, Ahmet
title: SARS‐CoV‐2 specific antibody responses in healthcare workers after a third booster dose of CoronaVac or BNT162b2 vaccine
date: 2022-04-23
journal: J Med Virol
DOI: 10.1002/jmv.27794
sha: 7a8aca0e49eb52fdd9a1e5f496da643742c003e2
doc_id: 691992
cord_uid: pj9p07vo

The first SARS‐CoV‐2 vaccination campaign in Turkey has started in mid‐January for the healthcare workers (HCWs) with the inactive virus vaccine CoronaVac (Sinovac). After four and a half months, the Turkish Ministry of Health rolled out a booster‐dose vaccination campaign for HCWs and all people over 50 years old beginning in July 2021. The individuals eligible were given the choice of either CoronaVac or mRNA vaccine BNT162b2 for the third booster‐dose vaccination. This study aimed to evaluate SARS‐CoV‐2 IgG antibody titers against the S1 subunit of the spike protein as a marker of the humoral response in 179 HCWs who received a third booster dose of either CoronaVac or BNT162b2. A total of 136 HCWs, 71 female (52.2%) and 65 male (47.8%), completed both serum collections on Days 0 and 28. The median SARS‐CoV‐2 IgG S Protein (SP) titer in all participants before the vaccination was 175.7 AU/ml. Of 136 HCWs, 103 (75.73%) chose BNT162b2 vaccine and 33 (24.26%) chose CoronaVac as the third booster dose. There was a significant difference between the BNT162b2 group and the CoronaVac group in terms of SARS‐CoV‐2 IgG SP titers (p < 0.001). The median SARS‐CoV‐2 IgG SP titers in BNT162b2 group (n = 103) and in CoronaVac group (n = 33) were 17619.3 AU/ml and 1153.0 AU/ml, respectively. The third booster dose with BNT162b2 and CoronaVac increased antibody titers in each participant a mean of 162‐fold and 9‐fold, respectively. HCWs in the BNT162b2 group reported more frequent adverse events than HCWs in the CoronaVac group (p < 0.001).

| 1 a variant of concern, a variant with one or more mutations that allow the virus to infect people more easily or spread from person to person more easily, making the virus less responsive to treatments or affect how well vaccines work against the virus. 4 The Delta variant is highly transmissible, estimated to be about 60%-100% more transmissible than the previous dominant Alpha variant. 4, 5 The CDC has suggested its basic reproduction rate (R0, i.e., the estimated number of secondary cases of infections that are transmitted from an infected person to a susceptible population) was 5-8. 4 to 67% with the delta variant. 7 A recent study from Thailand reported that CoronaVac, an inactivated whole virus vaccine (Sinovac) used in some countries such as Turkey, Chile, Thailand, Brazil, and Indonesia, provided a low degree of neutralization-afforded protection when compared with natural infection. The researchers concluded that further booster doses, heterologous or otherwise, might be needed for recipients of CoronaVac to maintain a long-term anamnestic response. 8 Another explanation suggested for the Delta variant surge was the waning immunity of both natural infection and SARS-CoV-2 vaccines. 6 It was shown that neutralizing antibody responses after natural infection declines over time. 9 Recently, a preliminary study from Israel assessed the correlation between the time from the BNT162b2 (Pfizer-BioNTech) vaccine and the incidence of breakthrough infections and found that the risk for infection was significantly higher for early vaccinees compared to those vaccinated later. 10 Due to the emergence of the Delta variant and preliminary evidence of waning immunity both after natural infection and vaccination, decision-makers in different countries have developed various policy recommendations. 2 CDC distinguishes a "third dose" from a "booster dose". An additional (third) dose of an mRNA COVID-19 vaccine (Pfizer-BioNTech or Moderna) at least 28 days after completing the initial 2-dose mRNA COVID-19 vaccine series was recommended to moderately to severely immunocompromised individuals who failed to build immunity after the two initial doses.

On the other hand, CDC defines a "booster dose" as another dose of a vaccine that is given to someone who built enough protection initially after vaccination, but then that protection decreased over time due to waning immunity. 11 Table 1 .

The median SARS-CoV-2 IgG SP titer in all participants before the vaccination with the third booster dose was 175.7 AU/ml (min: 10 .90 AU/ml, max: 5201.60 AU/ml). Antibody titers were below the threshold (50 AU/ml) in 11 (8%) HCWs. In HCWs who currently smoke, antibody titers were found to be lower compared to nonsmokers (p = 0.034), and antibody titers in HCWs with a previous COVID 19 history were found to be higher compared to it should be kept in mind that we did not proceed with dilutions to quantify the titers over 40 000 AU/ml which was the maximum antibody titer level that the test could report in default. 22 There are a few studies that used the same testing method the present study used to evaluate the immunogenicity of recommended The present study had some limitations. It was conducted in a single center, and the sample size was relatively small. The participants with asymptomatic infection could not be detected in the time between vaccination and sampling, so the antibodies elicited from a silent natural infection may have altered antibody levels.

Additionally, the assay we used was not a direct measurement of neutralizing antibody levels which were suggested to be highly predictive of immune protection from symptomatic SARS-CoV-2

infection. 42 However, it was reported that it was in agreement with a neutralization method (positive agreement, 100.0%; 95% CI, 95.72%-100.00%). 17 vaccine.

The authors declare no conflicts of interest.

The data presented in this study are available as Supporting Information: Appendix file.

Ethical approval was obtained from the Ethics Committee of Samsun 

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Supporting Information section at the end of this article. How to cite this article

SARS-CoV-2 specific antibody responses in healthcare workers after a third booster dose of CoronaVac or BNT162b2 vaccine