Safety And Protection Of The Inactivated COVID-19 Vaccine On Pregnant Mice And Offspring Mic

The Coronavirus Disease 2019(COVID-19)pandemic,caused by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2),began in December 2019.As of January 2023,there have been over 760 million confirmed cases and 6.87 million deaths worldwide.This unprecedented pandemic has put enormous pressure on global public health and medical systems.Mass vaccination against COVID-19 is considered one of the most effective measures to combat the disease.China has already started an orderly COVID-19 vaccination program using inactivated vaccines,which has shown good safety and immunogenicity in healthy adults(aged 18-59)and those aged over 60,and has been further extended to the 3-17 age group.However,during the clinical trials of COVID-19 vaccines,several special populations were not included in sufficient numbers,such as pregnant and breastfeeding women,rheumatologic and autoimmune disorders,cancer,transplant recipients,chronic liver diseases,end-stage renal disease,psychiatric disorders,human immunodeficiency virusand immunocompromised individuals etc.Therefore,conducting preclinical safety and efficacy studies of inactivated COVID-19 vaccines for these special populations is of significant importance in providing basic research data for clinical use.Part Ⅰ.Safety and protective effects of the inactivated SARS-CoV-2 vaccine in pregnant and lactational hACE2 miceTo protect pregnant women and fetuses,pregnant women were not included in the research subject during the development of phases Ⅰ,Ⅱ,and Ⅲ clinical trials of the inactivated COVID-19 vaccine,which has resulted in limited safety and efficacy data during pregnancy and lactation period,and widespread promotion of the vaccine in pregnant women has not been achieved.Whether vaccination of pregnant women or women of childbearing age has adverse effects on pregnancy or fetuses,and whether it can protect pregnant women and fetuses from SARS-CoV-2 infection,lack clinical data support in the early stages of the COVID-19 pandemic,resulting in high reluctance of vaccination for pregnant women or women of childbearing age.However,compared with women of childbearing age who are not pregnant,pregnant women have an increased risk of adverse pregnancy outcomes caused by COVID-19 infection,including preeclampsia,preterm birth,stillbirth,and also increased risk of infection for infants after delivery.Therefore,studying the non-clinical safety and efficacy of the inactivated COVID-19 vaccine on pregnant animals has guiding significance for the vaccination of pregnant women.We used SARS-CoV-2 susceptible human angiotensin-converting enzyme 2(hACE2)mice as the research subjects to study the effects of the inactivated COVID-19 vaccine on pregnancy and offspring growth and development,as well as their adult behavioral aspects.The hACE2 mice were immunized before and during pregnancy with two doses of Corona Vac(the inactivated COVID-19 vaccine,Sinovac Biotech),and the results showed that the mice’s weight and reproductive performance were normal,and the offspring’s physical development was also normal.Moreover,we discovered that using 100 50%tissue culture infectious dose(TCID50)of SARS-CoV-2 in intranasal infection of pregnant mice on day 13 of pregnancy,resulted in all unimmunized pregnant mice dying before giving birth,while all immunized pregnant mice survived,and their reproductive performance and offspring physical development were normal.Our research results indicate that the administration of Corona Vac is safe for hACE2 mice during pregnancy and offspring growth and development,can effectively protect pregnant mice from SARS-CoV-2 infection,and infection after immunization does not affect the growth and development of their offspring,suggesting that the vaccination with the inactivated COVID-19 vaccine may be an effective strategy to prevent infection in pregnant women.To study the effects of immunization and subsequent SARS-CoV-2 infection on offspring(F1 generation)adult behavior,we conducted research on their free activity behavior and spatial learning and memory abilities.Results from the open field test showed no significant differences in cumulative distance travelled,movement speed,movement time,and center time of movement in the F1 generation(P>0.05);while the Morris water maze test showed no significant differences in the latent movement distance in each training day,as well as the number of platform crossings,the first latent period of crossing the platform,and the saved time in the platform quadrant during the exploration stage of the F1 generation(P>0.05).Our research results indicate that immunization and subsequent SARS-CoV-2 infection in the F0 generation have no significant effect on the free activity behavior,spatial reference,and learning and memory abilities of the adult F1 generation.Part II.The protection of Corona Vac against the infection of SARS-CoV-2(WH-09)and Omicron variant in nude-hACE2 miceImmune-compromised individuals are at higher risk of developing severe consequences after SARS-CoV-2 infection,but the underlying mechanisms and the protective effect of vaccines are not fully understood.One of the important reasons why this population is not included in phase Ⅲ clinical vaccine trials is that immune deficiency can impair the humoral and cellular immune responses induced by vaccines,making it difficult to measure the effectiveness of vaccination in the immune system.Nude mice are a mouse strain with a spontaneous deficiency of the Foxnl gene,which can result in thymic degeneration or absence,leading to immunosuppression and a decrease in the number of T cells,and is commonly used in preclinical evaluations of disease in immune-compromised populations.Therefore,in this study,we constructed a nude-hACE2 mouse model and investigated the protective effect of CoronaVac vaccination against infection with SARS-CoV-2(WH-09)or Omicron variant in nude-hACE2 mice.Our study found that,compared to the infection-only group,nude-hACE2 mice infected with SARS-CoV-2(WH-09)after CoronaVac vaccination showed reduced viral load in their brain and lung tissue,as well as a reduction in histopathological symptoms.Compared to the infection-only group,nude-hACE2 mice infected with Omicron variant after CoronaVac vaccination showed reduced viral load in their brain and lung tissue,but no significant improvement in histopathological symptoms was observed.Overall,CoronaVac vaccination showed limited protective effects against infection with SARS-CoV-2(WH-09)and Omicron variant in nude-hACE2 mice,providing basic research data for the vaccination of immune-compromised populations with SARS-CoV-2 vaccines in clinical settings.