Third-generation smallpox vaccines induce low-level cross-protecting neutralizing antibodies against Monkeypox virus in laboratory workers

Abstract

Due to the discontinuation of routine smallpox vaccination after its eradication in 1980, a large part of the human population remains naïve against smallpox and other members of the orthopoxvirus genus. As a part of biosafety personnel protection programs, laboratory workers receive prophylactic vaccinations against diverse infectious agents, including smallpox. Here, we studied the levels of cross-protecting neutralizing antibodies as well as total IgG induced by either first- or third-generation smallpox vaccines against Monkeypox virus, using a clinical isolate from the 2022 outbreak. Serum neutralization tests indicated better overall neutralization capacity after vaccination with first-generation smallpox vaccines, compared to an attenuated third-generation vaccine. Results obtained from total IgG ELISA, however, did not show higher induction of orthopoxvirus-specific IgGs in first-generation vaccine recipients. Taken together, our results indicate a lower level of cross-protecting neutralizing antibodies against Monkeypox virus in recipients of third-generation smallpox vaccine compared to first-generation vaccine recipients, although total IgG levels were comparable.

Keywords: ELISA; Imvamune/Imvanex/Jynneos; Monkeypox virus; Neutralizing antibodies; Occupational biosafety; Vaccines; Vaccinia virus; serum neutralization test.

Fig. 1

Serum VACV and MPXV nAb titers of immunized study participants. (A) VACV and (B) MPXV nAb titers illustrated by reciprocal serum dilution. Each individual is represented by a separate bar while each plotted value represents a different year of sampling. Serum nAbs of individuals were aligned from highest to lowest titer. Comparison of serum nAb titers of first- and third-generation vaccine recipients against (C) VACV and (D) MPXV. Statistical significance was evaluated through Mann-Whitney t-test (***p = 0.0003). Dashed lines: limit of detection, 1:10 dilution. Reciprocal serum dilution: virus neutralization >50 % compared to control.

Fig. 2

Serum nAb titers of first-generation vaccine recipients with or without a booster dose of Imvamune/Imvanex. (A) Serum VACV nAb titers of laboratory workers vaccinated by first-generation vaccine with (orange bars) and without (white bars) a booster dose, illustrated by the reciprocal serum dilution. (B) Comparison of VACV nAb titers between individuals with and without a booster dose. (C) Serum MPXV nAb levels of laboratory workers with or without a booster dose. (D) Comparison of MPXV nAb titers of first-generation vaccine recipients and those who received a booster dose. Serum nAbs titers of individuals listed in panels (A) and (C) are in the same order, for comparison of VACV and MPXV nAb titers. Statistical significance was evaluated through Mann-Whitney t-test (ns, non-significant p = 0.1014, 0.2343, respectively) The dashed lines: limit of detection, 1:10 dilution. Reciprocal serum dilution: virus neutralization >50 % compared to control.

Fig. 3

Serum nAb titers of serum samples collected in 2022 from active laboratory workers. (A) MPXV nAb titers illustrated by the reciprocal serum dilution. Each individual is illustrated by a separate bar. Serum nAb titers of individuals are aligned from highest to lowest titer. (B) Comparison of serum MPXV nAb titers grouped in first- and third-generation vaccine recipients. (C) VACV nAb titers similarly illustrated. (D) Comparison of serum VACV nAb titers grouped in first- and third-generation vaccine recipients. Statistical significance was determined with a Mann-Whitney t-test (**p = 0.0019, ***p = 0.0007). Dashed lines: limit of detection, 1:10 dilution. Reciprocal serum dilution: virus neutralization >50 % compared to control.

Fig. 4

Orthopoxvirus-specific IgGs in the serum of study participants immunized either by first- or third-generation vaccines. (A) Total orthopoxvirus-specific IgG of laboratory workers illustrated by units/ml derived from a standard curve. Serum samples included were collected from 2014 to 2021. (B) Comparison of serum orthopoxvirus-specific IgG of laboratory workers grouped according to vaccine administered. (C) Orthopoxvirus-specific IgG levels of serum samples from active laboratory workers collected in 2022. (D) Group comparison of orthopoxvirus-specific IgG levels of serum samples taken in 2022, during the active MPXV outbreak. Statistical significance was determined by Mann-Whitney t-test (**p = 0.0012,0.0027, respectively; p = 0.0513, p = 0.5912, non-significant, ns). Each bar shows an individual study participant, whereas each plotted value represents a different year of serum collection. IgG levels are aligned from highest to lowest concentration. Dashed lines: range of positive control, negative controls: sera from non-immunized laboratory workers.