ABSTRACT
Prominent genomic recombination has been observed between the Delta and Alpha variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) isolated from clinical specimens in Japan. It is necessary to intensively study such marked genetic variations and characterize the emerging variants after careful verification of their lineage and clade assignment.
Subject(s)
Coronavirus Infections , Severe Acute Respiratory Syndrome , Genetic Diseases, InbornABSTRACT
Since little is known about viral and host characteristics of breakthrough infections after COVID-19 vaccination, a nationwide investigation of breakthrough cases was initiated in Japan. 130 cases (90%+ received mRNA vaccines) were reported with respiratory specimens in 117 cases and sera in 68 cases. A subset of cases shed infectious virus regardless of symptom presence or viral lineages. Viral lineages for breakthrough infections matched both temporally and spatially with the circulating lineages in Japan with no novel mutations in spike receptor binding domain that may have escaped from vaccine-induced immunity were found. Anti-spike/neutralizing antibodies of breakthrough infections in the acute phase owing to vaccine-induced immunity were significantly higher than those from unvaccinated convalescent individuals but were comparable to vaccinated uninfected individuals, and followed by boosting in the convalescent phase. Symptomatic cases had low anti-spike/neutralizing antibodies in the acute phase with robust boosting in the convalescent phase, suggesting the presence of serological correlate for symptom development in COVID-19 vaccine breakthrough infections.