Developmental and reproductive toxicity of a recombinant protein subunit COVID-19 vaccine (ZF2001) in rats

ZF2001, a protein subunit vaccine against coronavirus disease 2019 (COVID-19), contains recombinant tandem repeat of dimeric receptor-binding domain (RBD) protein of the SARS-CoV-2 spike protein with an aluminium-based adjuvant. During the development of this vaccine, two nonclinical studies were conducted to evaluate female fertility, embryo-fetal development, and postnatal developmental toxicity in Sprague‒Dawley rats according to the ICH S5 (R3) guideline. In Study 1 (embryo-fetal developmental toxicity, EFD), 144 virgin female rats were randomly assigned into four groups and received three doses of vaccine (25 μg or 50 μg RBD protein/dose, containing the aluminium-based adjuvant), the aluminium-based adjuvant or a sodium chloride injection administered intramuscularly on days 21 and 7 prior to mating and on gestation day (GD) 6. In Study 2 (pre- and postnatal developmental toxicity, PPND), ZF2001 at a dose of 25 μg RBD protein/dose or sodium chloride injection was administered intramuscularly to female rats (n = 28 per group) 7 days prior to mating and on GD 6, GD 20 and postnatal day (PND) 10. There were no obvious adverse effects in dams, except for local injection site reactions related to the aluminium-based adjuvant (yellow nodular deposits in the interstitial muscle fibres). There were also no effects of ZF2001 on the mating performance, fertility or reproductive performance of parental females, embryo-fetal development, postnatal survival, growth, physical development, reflex ontogeny, behavioural and neurofunctional development, or reproductive performance of the offspring. The strong immune responses associated with binding and neutralising antibodies were both confirmed in dams and fetuses or offspring in these two studies. These results would support clinical trials or the use of ZF2001 in maternal immunisation campaigns, including those involving women with childbearing potential, regardless of pregnancy status.