High SARS-CoV-2 viral loads in respiratory secretions detected by PCR technique are usually an indicator of high transmission risk, but not always. In this article, we present the case of a fully-vaccinated patient with rapid clearance of the alpha variant of the virus.
A middle-aged woman tested negative for SARS-CoV-2 upon arrival after an international flight. She had been vaccinated with two doses of mRNA vaccine several weeks before and was routinely quarantined together with two of her children travelling together. On day 7 she tested positive by PCR with a very high virus load (Ct value 13.4, > 107 copies/ml), and antibodies against the spike protein increased rapidly from 3703 U/ml to 9447 U/ml on day 15. Subgenomic mRNA was detected, indicating active virus replication, and typical virus particles were observed by EM directly from a nasopharyngeal specimen. However, viral culture was negative, and the virus (Alpha variant B.1.1.7) was not transmitted to the other family members. Eight days later (day 15), still asymptomatic, she was PCR-negative, indicating a very efficient elimination of the virus. In this case, two doses of mRNA vaccine protected against clinical symptoms as well as household transmission of SARS-CoV-2.
A fully-vaccinated woman in her forties was placed in quarantine on returning home to Norway after travelling abroad. She tested negative for SARS-CoV-2 at the airport and had no respiratory symptoms. On day 7 following arrival, she had a positive result on nasopharyngeal polymerase chain reaction (PCR) testing (Alinity m, Abbott). A high viral load was detected in the specimen, with a cycle threshold (CT) of 13.4, corresponding to > 107 copies/mL (information from the manufacturer), although she was still asymptomatic.
Total levels of antibodies to the spike protein (Elecsys, Roche), which develop following infection as well as following vaccination, were high (3703 U/mL) on day 9 following arrival. Testing for antibodies to the SARS-CoV-2 nucleocapsid (Elecsys, Roche), which are only produced by current or past infection, was negative. On day 15, another nasopharyngeal specimen was taken, which was negative on PCR testing. A blood sample taken at the same time found that antibody levels to the spike protein had increased to 9447 U/mL. Antibodies to the nucleocapsid antigen were not detected until day 22, with levels rising rapidly on subsequent days.
Two of the patient's unvaccinated adult children travelled abroad with her and were also quarantined in the same house as their mother. They had four negative PCR tests and one negative antibody test, the last being eight days after their mother had tested positive for SARS-CoV-2.
The virus detected was an alpha variant (B.1.1.7), which gave a negative viral culture result in Vero-E6 cells (1). A PCR test was also performed, which was positive for mRNA, indicating active viral replication (2, 3). Transmission electron microscopy of the specimen revealed several round particles of a typical size (60–140 nm), with spike-like structures on the surface (Figure 1).
The patient and other people mentioned have given consent for the article to be published.
The article has been peer-reviewed.