SARS-CoV-2 Infections in mRNA Vaccinated Individuals are Biased for Viruses Encoding Spike E484K and Associated with Reduced Infectious Virus Loads that Correlate with Respiratory Antiviral IgG levels.

INTRODUCTION: COVID-19 large scale immunization in the US has been associated with infrequent breakthrough positive molecular testing. Whether a positive test is associated with a high viral RNA load, specific viral variant, recovery of infectious virus, or symptomatic infection is largely not known. METHODS: In this study, we identified 133 SARS-CoV-2 positive patients who had received two doses of either Pfizer-BioNTech (BNT162b2) or Moderna (mRNA-1273) vaccines, the 2nd of which was received between January and April of 2021. The positive samples were collected between January and May of 2021 with a time that extended from 2 to 100 days after the second dose. Samples were sequenced to characterize the whole genome and Spike protein changes and cycle thresholds that reflect viral loads were determined using a single molecular assay. Local SARS-CoV-2 IgG antibodies were examined using ELISA and specimens were grown on cell culture to assess the recovery of infectious virus as compared to a control unvaccinated cohort from a matched time frame. RESULTS: Of 133 specimens, 24 failed sequencing and yielded a negative or very low viral load on the repeat PCR. Of 109 specimens that were used for further genome analysis, 68 (62.4%) were from symptomatic infections, 11 (10.1%) were admitted for COVID-19, and 2 (1.8%) required ICU admission with no associated mortality. The predominant virus variant was the alpha (B.1.1.7), however a significant association between lineage B.1.526 and amino acid change S: E484K with positives after vaccination was noted when genomes were compared to a large control cohort from a matched time frame. A significant reduction of the recovery of infectious virus on cell culture as well as delayed time to the first appearance of cytopathic effect was accompanied by an increase in local IgG levels in respiratory samples of vaccinated individuals but upper respiratory tract IgG levels were not different between symptomatic or asymptomatic infections. CONCLUSIONS: Vaccination reduces the recovery of infectious virus in breakthrough infections accompanied by an increase in upper respiratory tract local immune responses. FUNDING: National Institute of Health (The Johns Hopkins Center of Excellence in Influenza Research and Surveillance, HHSN272201400007C), Johns Hopkins University, Maryland Department of Health, Centers for Disease Control and Prevention.