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Immunogenicity trends one and three months after second BNT162B2 vaccination among healthcare workers in Israel

Published:November 24, 2021DOI:https://doi.org/10.1016/j.cmi.2021.11.014

      Abstract

      Objectives

      We evaluated antibody response to the BNT162B2 vaccine among healthcare workers (HCWs) to identify factors associated with decreased immunogenicity.

      Methods

      This prospective cohort study included consenting HCWs who completed a questionnaire regarding background illnesses, medications, and post vaccination allergic reactions or rash. All HCWs were tested for anti-spike antibodies (LIAISON SARS-CoV-2 S1/S2 IgG assay) one and three months after second vaccine dose. A multivariate mixed linear model was adjusted to participant’s data and fit to predict antibody levels after second BNT162B2 vaccine dose, based on antibody levels at 1 month and the slope between 3 and 1 month. Multivariate analyses identified factors associated with lower antibody levels.

      Results

      A total of 1,506 HCWs were tested for SARS-CoV-2 antibodies. Older age was associated with lower mean antibody levels (-1.22 AU/ml, p <0.001, 95% CI -1.43 – -1.01). In addition, male (-22.16AU/ml, p <0.001, 95% CI -27.93 – -16.39), underlying condition (-10.86AU/ml, p= 0.007, 95% CI -18.81 – -2.91) and immunosuppressive treatment (-28.57AU/ml, p = 0.002, 95% CI -46.85 – -10.29) were associated with significantly lower mean antibody levels. Allergic reactions after vaccine administration or peri vaccination GCS treatment were not correlated with antibody levels.

      Conclusions

      Most HCWs had measurable antibodies at 3 months. Risk factors for lower antibody levels were older age, male sex, underlying condition, and immunosuppressive treatment. These factors may be considered when planning booster doses during vaccine shortage.

      Graphical abstract

      Keywords

      Introduction

      Since the World Health Organization (WHO) declared a pandemic for coronavirus disease-2019 (COVID-19), more than 3 million lives have been claimed worldwide; 6,363 were in Israel by May 2021 [

      World Health Organization (WHO). WHO Coronavirus Disease (COVID-19) Dashboard. Geneva: WHO. (Accessed: 1 May 2021). Available from: https://covid19.who.int/

      ]. In Israel, Pfizer/BioNTech BNT162b2 vaccination began in late December. By late April 2021, more than 5 million Israeli citizens were fully vaccinated [

      Ministry of Health of Israel. [Coronavirus in Israel – general situation]. Jerusalem, Israel: Ministry of Health. (Accessed: 1 May 2021). Hebrew. Available from: https://datadashboard.health.gov.il/COVID-19/general

      ]. Northern Israel’s only tertiary medical centre has been involved with the vaccination campaign from the beginning. Of its 5,499 healthcare workers (HCWs), 88% were fully vaccinated.
      The high effectiveness of the vaccine in Israel was published [
      • Dagan N.
      • Barda N.
      • Kepten E.
      • Miron O.
      • Perchik S.
      • Katz M.A.
      • et al.
      BNT162b2 mRNA Covid-19 vaccine in a nationwide mass vaccination setting.
      ,
      • Benenson S.
      • Oster Y.
      • Cohen M.J.
      • Nir-Paz R.
      BNT162b2 mRNA Covid-19 vaccine effectiveness among health care workers.
      ,
      • Amit S.
      • Regev-Yochay G.
      • Afek A.
      • Kreiss Y.
      • Leshem E.
      Early rate reductions of SARS-CoV-2 infection and COVID-19 in BNT162b2 vaccine recipients.
      ], but immunogenicity data is sparse, mainly among immunocompromised or haemodialysis patients, and after the first or second dose of the vaccine [
      • Grupper A.
      • Rabinowich L.
      • Schwartz D.
      • Schwartz I.F.
      • Ben-Yehoyada M.
      • Shashar M.
      • et al.
      Reduced humoral response to mRNA SARS-Cov-2 BNT162b2 vaccine in kidney transplant recipients without prior exposure to the virus.
      ,
      • Rabinowich L.
      • Grupper A.
      • Baruch R.
      • Ben-Yehoyada M.
      • Halperin T.
      • Turner D.
      • et al.
      Low immunogenicity to SARS-CoV-2 vaccination among liver transplant recipients.
      ,
      • Marinaki S.
      • Adamopoulos S.
      • Degiannis D.
      • Roussos S.
      • Pavlopoulou I.D.
      • Hatzakis A.
      • et al.
      Immunogenicity of SARS-CoV-2 BNT162b2 vaccine in solid organ transplant recipients.
      ]. A campaign to vaccinate all HCWs at our institution was launched on December 20, 2020.
      This brief report presents the antibody levels among HCWs, one and three months after the second vaccine dose.

      Methods

      A prospective cohort study was conducted on fully vaccinated HCWs who consented to participate and were tested for blood anti-spike SARS-CoV-2 levels one and three months after the second vaccine dose in February and April 2021, respectively. The study was conducted at Rambam Health Care Campus (RHCC), a 1,000 bed tertiary university hospital.
      LIAISON SARS-CoV-2 S1/S2 IgG assay (DiaSorin, Saluggia, Italy) was used to detect anti-spike S1/S2 IgG antibodies. The cut-off value was 15 AU/ml according to Israeli Ministry of Health instructions [

      Israel Ministry of Health Department of Laboratories. Performing serological tests to determine the presence of antibodies to the new corona virus – update 12/17/20. December 24, 2020. (Accessed: 1 May 2021). Available from: https://www.gov.il/BlobFolder/legalinfo/bz-306963420-1/he/files_publications_corona_bz-477860520.pdf [Hebrew]

      ].
      Primary outcome measures were the antibody levels difference at two time points (1 and 3 months) and the association between that difference and age, sex, underlying disease, peri-vaccination GCS, immunosuppressive therapy, and allergic reactions or rash after vaccination.
      All participants completed an online questionnaire including age, sex, underlying diseases (yes/no question with a dropdown list of conditions), peri-vaccination gluococorticosteroids (GCS), immunosuppressive therapy, post vaccination allergic reactions or rash, contact with patients with confirmed SARS-CoV-2 infection and flu-like illness after vaccination.
      Treatment with GCS was defined as either chronic or GCS treatment 1–2 days before or after vaccine administration to relieve allergic reactions.
      Increased antibody levels after 3 months were defined as any antibody level increase between 1 and 3 months.
      Individuals with increased antibody levels at 3 months were examined with Abbott ARCHITECT SARS-CoV-2 IgG assay to detect anti-NC antibodies to rule out asymptomatic SARS-CoV-2 infection. The positivity threshold was ≥1.4, using a lower, provisional “grey-zone threshold” (≥0.5–1.39) to improve diagnostic yield. All HCWs with signs and symptoms suggesting SARS-CoV-2 infection were examined with molecular assay (polymerase chain reaction).
      Data were analysed by SPSS software (version 27). A multivariate linear mixed model was fit to predict the adjusted difference of 3-month antibody levels by the 1-month level and by baseline participant characteristics as potential predictors (specifically age, sex, presence of underlying condition, peri-vaccination GCS, immunosuppressive therapy, and allergic reactions or rash following vaccine administration). The model also included the time after second vaccine dose (1 and 3 months).
      The study was approved by the hospital’s Internal Review Board (#021-021).

      Results

      Overall, 1,506 HCWs were evaluated at 1 month and 1,209 (80.3%) at 3 months; 1,194 (79.3%) were evaluated at both time points. At 1 month, 6 participants had negative serology (0.4%), of which only 3 were retested at 3 months and remained seronegative.
      Of the 1 month participants, 4 were seropositive (21–58 AU/ml) and became seronegative at the 3 month evaluation point.
      At 3 months, a total of 7 HCWs were seronegative, 5 of which were >60 years old including 2 with underlying disease. Two younger HCWs were also seronegative and had underlying disease.
      Mean age was 48.39±12.47 (range 19–91) and the female to male ratio was 2.5:1. Underlying conditions were reported in 211 (14%) participants: hypothyroidism, 134 (8.9%); autoimmune disease, 94 (6.2%); cardiac disease, 51 (3.4%); lung disease, 47 (3.1%); immunodeficiency, 29 (1.9%); chronic renal disease, 9 (0.6%); and active oncological disease, 7 (0.5%). Peri-vaccination GCS or long-term immunosuppressive therapy was reported by 74 (4.9%) HCWs.
      Seven participants were diagnosed with SARS-CoV-2 infection, of which 6 were diagnosed less than 7 days after the second vaccine dose. One participant was diagnosed one and half months after the second dose; this individual was mildly symptomatic and had increased antibody levels 3 months after vaccination.
      At 1 month, age correlated inversely with antibody levels: for each 1 year increase in age a 1.39 AU/ml decrease in antibody levels was noted (95% CI -1.64 – -1.13 p <0.001). Male sex was associated with a mean decrease of 23.08 AU/ml in antibody levels compared to females (p <0.001, 95% CI -30.01 – -16.16). Underlying condition and immunosuppressive treatment were also associated with reduction from baseline in mean antibody levels (13.44 AU/ml, p=0.005, 95% CI -22.80 – -4.08 and 35.23 AU/ml, p=0.002, 95% CI -57.48 – -12.98, respectively).
      At 3 months, for each 1 year increase in age, a 0.87 AU/ml decrease in antibody levels was observed (p <0.001, 95% CI -1.12 – -0.62). Males had lower antibody levels (by 19.10 AU/ml) compared to females (p <0.001, 95% CI -25.84 – -12.37), and participants receiving immunosuppressive treatment had lower antibody levels (by 35.71 AU/ml) (p <0.001, 95% CI -57.36 – -14.06) than those not receiving it.
      The mixed linear model showed that antibody levels were significantly lower at the 3-month time point compared to 1-month (-58.63AU/ml, p <0.001, 95% CI -60.95 – -56.32). The older the participant, the lower the mean antibody levels; in addition, male sex, underlying condition, and immunosuppressive treatment predicted significantly lower mean antibody levels. Allergic reactions after vaccine administration or peri-vaccination GCS treatment were not correlated with antibody levels (Table 1). No interaction was found between age group and sex. Figure 1 presents the mean antibody titer distribution by age group.
      Table 1Multivariate mixed linear model to predict antibody levels adjusted to participants characteristics after second BNT162B2 and based on antibody levels at 1 month.
      ParameterFirst Sample at One Month (N=1506)Second Sample at Three Months (N=1209)Mixed Linear Model (N=1506)
      EstimateP Value95% CIEstimateP Value95% CIEstimateP Value95% CI
      Age (years)-1.39<0.001-1.64 – -1.13-0.87<0.001-1.12 – -0.62-1.22<0.001-1.43 – -1.01
      SexFemaleReferenceReferenceReference
      Male-23.08<0.001-30.01 – -16.16-19.10<0.001-25.84 – -12.37-22.16<0.001-27.93 – -16.39
      Underlying

      Condition
      NoReferenceReferenceReference
      Yes-13.440.005-22.80 – -4.08-10.230.028-19.34 – -1.12-10.860.007-18.81 – -2.91
      GCS Tx

      Peri-vaccination
      NoReferenceReferenceReference
      Yes20.290.051-0.10 – 40.664.200.678-15.63 – 24.04-1.050.905-18.38 – 16.27
      Immunosuppressive TherapyNoReferenceReferenceReference
      Yes-35.230.002-57.48 – -12.98-35.710.001-57.36 – -14.06-28.570.002-46.85 – -10.29
      Allergic ReactionNoReferenceReferenceReference
      Yes5.770.468-9.83 – 21.36- 0.340.965-15.51 –14.841.210.866-12.87 – 15.29
      Time point1-monthReference
      3-month-58.63<0.001-60.95 – -56.32
      Figure 1
      Figure 1Boxplot of Mean Serology Titer According to Age Group.
      Supplemental Figure 1 presents median antibody levels at 1 and 3 months and a significant absolute reduction in antibody levels at 3 and 1 months in concordance with age (0.542 AU/ml, p <0.001, 95% CI 0.350–0.073).
      Of 1,194 HCWs fully vaccinated and screened for antibody levels at both time points, only 66 had increased antibody levels at 3 months, of which only one was diagnosed with SARS-CoV-2 infection; the rest were anti-NC antibody negative at both 1 and 3 months. No risk factors were identified compared with other participants, except for a higher SARS-CoV-2 exposure rate in the group with decreasing antibody levels, but this was not statistically significant (Supplemental Table 1).

      Discussion

      Three months after full BNT162b2 vaccination, most tested HCWs still had a measurable level of SARS-CoV-2 antibodies, with 0.6% seronegative cases and only one SARS-CoV-2 confirmed case. Lower levels were associated with older age, male sex, and underlying condition, as well as immunosuppressive therapy.
      When examining healthy populations similar to our HCWs, age is a key factor in measured antibody levels, with the lowest levels seen among participants >60 years old. Other studies examining serology after BNT162b2 vaccination have demonstrated similar results 1 month or less after vaccination among healthy participants, as well as patients with immunodeficiency and haemodialysis (6–8,10,11]. A study conducted in Israel observed lower antibody levels after the first BNT162b2 dose among older HCWs, especially >60 years old [
      • Abu Jabal K.
      • Ben-Amram H.
      • Beiruti K.
      • Batheesh Y.
      • Sussan C.
      • Zarka S.
      • et al.
      Impact of age, ethnicity, sex and prior infection status on immunogenicity following a single dose of the BNT162b2 mRNA COVID-19 vaccine: real-world evidence from healthcare workers, Israel, December 2020 to January 2021.
      ]. Another recent study followed Israeli HCWs up to 5 weeks after the second vaccine dose, and also demonstrated lower levels among those >66 years, males, and HCWs with other chronic conditions or immunodeficiency (12).
      An important observation from our data is the lower antibody levels found among males and those with an underlying condition both 1 and 3 months after BNT162b2 vaccination. This finding is supported by other studies and is also seen after other vaccinations (e.g., hepatitis B vaccine and measles) [
      • Zimmermann P.
      • Curtis N.
      Factors That influence the immune response to vaccination.
      ,
      • Ranjeva S.
      • Subramanian R.
      • Fang V.J.
      • Leung G.M.
      • Ip D.K.M.
      • Perera R.A.P.M.
      • et al.
      Age-specific differences in the dynamics of protective immunity to influenza.
      ,
      • Plotkin S.A.
      Correlates of protection induced by vaccination.
      ,
      • Plotkin S.A.
      Immunologic correlates of protection induced by vaccination.
      ].
      The difference in antibody levels between 3 and 1 month revealed a smaller absolute decrease in antibody levels as age increased. However, the absolute antibody levels at 1 month were also lower as age increased, indicating that the relative reduction does not differ by age. This finding should be further studied and correlated with clinical efficacy.
      Nevertheless, the fact that only 7 people had no measurable antibodies and were not infected with SARS-CoV-2 is encouraging; these HCWs will be followed. Future studies could provide insight regarding the decrease in antibody levels and its significance.
      Also interesting was the lack of association between reported post vaccination allergic reactions or rash, and antibody levels, which was also reported by Grupper et al. among transplant patients [
      • Grupper A.
      • Rabinowich L.
      • Schwartz D.
      • Schwartz I.F.
      • Ben-Yehoyada M.
      • Shashar M.
      • et al.
      Reduced humoral response to mRNA SARS-Cov-2 BNT162b2 vaccine in kidney transplant recipients without prior exposure to the virus.
      ].
      Finally, a small group of HCWs experienced increased antibody levels between 1 and 3 months. No association was found; these HCWs should be further followed up, and more research is needed to understand this phenomenon and its clinical significance, which is currently unknown.
      Our study had several limitations. Firstly, no information was available regarding cellular immunity and/or neutralizing antibodies, nor the protection from asymptomatic carriage or infection. There have been reports regarding neutralizing antibodies indicating a correlation between anti-S antibody titres and neutralization antibody levels after BNT162b2 vaccine [
      • Sahin U.
      • Muik A.
      • Derhovanessian E.
      • Vogler I.
      • Kranz L.M.
      • Vormehr M.
      • et al.
      COVID-19 vaccine BNT162b1 elicits human antibody and T H 1 T cell responses.
      ]. Secondly, our cohort of HCWs were generally healthy and young, with no very old individuals. The rise in antibody titer in 66 HCWs was not detected early enough to perform a molecular test, which might have verified SARS-CoV-2 diagnosis; however, that group was asymptomatic and exposed to fewer infected people. This group should be further followed.

      Conclusion

      Our findings are encouraging since most HCWs had measurable antibodies at 3 months with a low number of subsequently confirmed SARS-CoV-2 cases. Despite lower antibody levels among HCWs who were older, males, or receiving immunosuppressive treatment, their reduction in antibody levels was lower than in the other groups, which is also encouraging.

      Conflict of interest

      None declared.

      Funding statement

      No special funding was given for this study.

      Author Contributions

      YSM, KH, HDY, and MSC wrote the manuscript; YSM, KH, HDY, and MH conceived and designed the study; MSC did the laboratory testing; YSM, KH, HDY, AW, MM, GH, NH, VG, IN, HC, JT, and NP coordinated the patient enrolment and blood testing; HDY and RA conducted the statistical analysis; and HDY, KH, MSC, RA, and YSM performed data preparation.
      All authors read and approved the submission.

      Uncited References

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      Acknowledgements

      This study was performed in collaboration with the Israeli Ministry of Health. The authors would like to thank Mira Shiloah, Nelly Zaltzman Bershadsky, Rotem Cohen, Rotem Daniel, Sara Tzafrir, Marianna Sherman, Anat Reiner-Benaim, Ronit Leiba, and Deborah Hemstreet for their contributions toward the preparation of this manuscript.

      Appendix A. Supplementary data

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