Research Assistant Professor Louisiana State University, Louisiana, United States
Disclosure(s):
Tianyi Zhang, PhD: No financial relationships to disclose
Introduction/Rationale: SARS-CoV-2 spike–based vaccines control COVID-19, yet vaccine-associated enhanced respiratory disease (VAERD) after breakthrough infection remains a concern. We previously reported Th2/Th17-skewed VAERD in hACE2 mice, however, the mechanisms, durability, and effects of vaccine types and routes in this process are unclear and will be investigated here.
Methods: Wild-type mice received spike protein plus alum/CpG and were challenged with MA10 strain 14 days or 7 months post-boost. Parallel cohorts received intramuscular (IM) mRNA vaccines (Comirnaty or Spikevax) and were challenged at 7 months. Splenocytes were restimulated with spike peptide subpools to map Th2/Th17-associated epitopes. B cell or ITK deficient mice were used to define signaling requirements. We also used model antigen ovalbumin (OVA) as a control to test whether the observed Th2/Th17 phenotype is uniquely associated with intranasal spike following IM subunit vaccination. To further assess booster safety, IM mRNA vaccinated mice were boosted with intramuscular mRNA vaccine or intranasal Ad5-Spike.
Results: Despite protection, adjuvanted protein vaccination caused severe lung pathology with CD4⁺ T infiltration and elevated Th2/Th17 cytokines, persisting to 7 months. mRNA vaccines did not induce Th2/Th17-associated VAERD at delayed challenge. Th2/Th17-linked epitopes localized to S1, and both B cells and ITK signaling were required for pulmonary inflammation. Compared with OVA, intranasal spike after intramuscular adjuvanted vaccination recruited additional lung Th17 cells. For boosting, intramuscular mRNA was markedly safer than intranasal Ad5-Spike, which triggered robust Th2/Th17 inflammation.
Conclusion: VAERD risk can persist long after vaccination and depends on platform and delivery route. Intramuscular mRNA vaccines show superior safety, while spike contains epitopes capable of driving Th2- and Th17-mediated pathology, highlighting the need to refine spike antigens and booster strategies for durable, safe protection.
