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Densely sampled viral trajectories suggest longer duration of acute infection with B.1.1.7 variant relative to non-B.1.1.7 SARS-CoV-2

Our take —

This manuscript, available as a preprint and thus not yet peer reviewed, shows that infection with the B.1.1.7 variant of SARS-CoV-2 is associated with a longer duration of infection, which may help explain increased transmissibility of the B.1.1.7 variant. However, only a limited number (n=65) of individuals were included in this study, of which only 7 were infected with the B.1.1.7 variant. The conclusions should be interpreted with caution until further studies with larger, more representative cohorts can be conducted.

Study design

Retrospective Cohort

Study population and setting

This study compared the duration of SARS-CoV-2 infection in individuals infected with the B.1.1.7 variant to those infected by non-B.1.1.7 virus. The study population was selected from an initial pool of 298 individuals who were affiliated with a professional sports league in the United States (players and staff) and who first tested positive for SARS-CoV-2 between November 28, 2020 and January 20, 2021. From this initial pool, a convenience sample was chosen of 65 individuals who had at least 5 positive PCR tests (nasopharyngeal swabs), of which at least one had a cycle threshold (Ct) value of less than 35. Of the 65 included individuals, 7 were found to have been infected with the B.1.1.7 variant. Daily surveillance testing of the 65 included individuals allowed the authors to track the duration of infection in each person, and to perform comparisons between individuals infected with the B.1.1.7 variant versus non-B.1.1.7 virus.

Summary of Main Findings

The authors found that acute infection with B.1.1.7 was associated with more sustained nasopharyngeal viral concentrations than infection with non-B.1.1.7 virus. Specifically, they found that individuals infected with B.1.1.7 had a mean proliferation time (time from first detectable virus to peak viral concentration) of 5.3 days, and a mean clearance time (time from peak viral concentration to initial return to limit of detection) of 8.0 days, resulting in a mean overall duration of infection of 13.3 days. Individuals infected with non-B.1.1.7 had a mean proliferation time of 2.0 days, and a mean clearance time of 6.2 days, resulting in a total duration of infection of 8.2 days. They also found a slight difference in the mean peak viral concentration: 19 Ct (B.1.1.7) versus 20.2 Ct (non-B.1.1.7).

Study Strengths

Daily surveillance of all infected individuals allowed the authors to accurately determine the beginning, maximum, and end of detectable viral infection.


This study has a number of limitations: (1) The samples included were a convenience sample from within a specific population (individuals associated with a professional sports league) and therefore may not be representative of the general population. Similarly, no information was provided about the age or underlying conditions of these individuals (both of which are known to affect SARS-CoV-2 manifestation), and the final population was 90% male. (2) The study was conducted on a small number of samples (65), with only 7 belonging to the group of interest (B.1.1.7). Additional research is needed to determine if the findings presented hold true in a larger (and more diverse) population and if the observed differences (e.g., mean peak viral concentration of 19 versus 20.2 Ct) are statistically significant.

Value added

This paper is the first to suggest that there may be differences in duration of infection between individuals infected with B.1.1.7 versus non-B.1.1.7 SARS-CoV-2 variants. A difference in duration of infection may explain increased transmissibility of B.1.1.7, the reason for which is currently unknown.

This review was posted on: 5 March 2021