The rapid mutation of SARS-CoV-2 has led to multiple rounds of large-scale breakthrough infection and reinfection worldwide. However, the dynamic changes of humoral and cellular immunity responses to several subvariants after infection remain unclear. In our study, a 6-month longitudinal immune response evaluation was conducted on 118 sera and 50 PBMC samples from 49 healthy individuals who experienced BA.5/BF.7/XBB breakthrough infection or BA.5/BF.7-XBB reinfection. By studying antibody response, memory B cell, and IFN-γ secreting CD4⁺/CD8⁺ T cell response to several SARS-CoV-2 variants, we observed that each component of immune response exhibited distinct kinetics. Either BA.5/BF.7/XBB breakthrough infection or BA.5/BF.7-XBB reinfection induces relatively high level of binding and neutralizing antibody titers against Omicron subvariants at an early time point, which rapidly decreases over time. Most of the individuals at 6 months post-breakthrough infection completely lost their neutralizing activities against BQ.1.1, CH.1.1, BA.2.86, JN.1 and XBB subvariants. Individuals with BA.5/BF.7-XBB reinfection exhibit immune imprinting shifting and recall pre-existing BA.5/BF.7 neutralization antibodies. In the BA.5 breakthrough infection group, the frequency of BA.5 and XBB.1.16-RBD specific memory B cells, resting memory B cells, and intermediate memory B cells gradually increased over time. On the other hand, the frequency of IFN-γ secreting CD4⁺/CD8⁺ T cells induced by WT/BA.5/XBB.1.16 spike trimer remains stable over time. Overall, our research indicates that individuals with breakthrough infection have rapidly declining antibody levels but have a relatively stable cellular immunity that can provide some degree of protection from future exposure to new antigens.

Haemaphysalis longicornis, a three-host tick with a wide host range, is widely distributed in different countries and regions. It stands out among ticks due to its unique feature of having both parthenogenetic and bisexual populations. Despite their morphological resemblance, the characteristics of the parthenogenetic population have been overlooked. In this comprehensive study, we systematically compared the similarities and differences between these two populations. Our investigation revealed that the parthenogenetic H. longicornis, widely distributed in China, was found in ten provinces, surpassing the previously reported distribution. Notably, individuals from the parthenogenetic population exhibited a prolonged blood-feeding duration during the larval and nymph stages compared to their bisexual counterparts. Additionally, the life cycle of the parthenogenetic population was observed to be longer. A flow cytometry analysis indicated a DNA content ratio of approximately 2:3 between the bisexual and parthenogenetic populations. A phylogenetic analysis using whole mitochondrial genome sequences resulted in the separation of the phylogenetic tree into two distinct branches. A molecular analysis unveiled a consistent single T-base deletion at nucleotide 8497 in the parthenogenetic population compared to the bisexual population. Both populations displayed high viral infection capability and significant resistance to ivermectin. Intriguingly, despite these differences, the parthenogenetic population exhibited a similar life cycle to the bisexual population, retaining the ability to transmit pathogens such as Severe fever with thrombocytopenia syndrome virus (SFTSV) and Heartland Virus (HRTV). These findings contribute to a deeper understanding of the distinct characteristics and similarities between different populations of H. longicornis, laying the foundation for future research in this field.

Evidence of antibody-dependent enhancement (ADE) of other viruses has raised concerns about the safety of SARS-CoV-2 vaccines and antibody therapeutics. In vitro studies have shown ADE of SARS-CoV-2 infection. In this study, we also found that vaccination/convalescent sera and some approved monoclonal antibodies can enhance SARS-CoV-2 infection of FcR-expressing B cells in vitro. However, the enhancement of SARS-CoV-2 infection can be prevented by blocking Fc–FcR interaction through the addition of human serum/IgG or the introduction of mutations in the Fc portion of the antibody. It should be noted that ADE activity observed on FcR-expressing cells in vitro may not necessarily reflect the situation in vivo; therefore, animal and clinical data should be included for ADE evaluation.