Quarantine and serial testing for variants of SARS-CoV-2 with benefits of vaccination and boosting on consequent control of COVID-19

Abstract

Quarantine and serial testing strategies for a disease depend principally on its incubation period and infectiousness profile. In the context of COVID-19, these primary public health tools must be modulated with successive SARS CoV-2 variants of concern that dominate transmission. Our analysis shows that (1) vaccination status of an individual makes little difference to the determination of the appropriate quarantine duration of an infected case, whereas vaccination coverage of the population can have a substantial effect on this duration, (2) successive variants can challenge disease control efforts by their earlier and increased transmission in the disease time course relative to prior variants, and (3) sufficient vaccine boosting of a population substantially aids the suppression of local transmission through frequent serial testing. For instance, with Omicron, increasing immunity through vaccination and boosters-for instance with 100% of the population is fully immunized and at least 24% having received a third dose-can reduce quarantine durations by up to 2 d, as well as substantially aid in the repression of outbreaks through serial testing. Our analysis highlights the paramount importance of maintaining high population immunity, preferably by booster uptake, and the role of quarantine and testing to control the spread of SARS CoV-2.

Keywords: disease time course; omicron; public health; severe acute respiratory syndrome; variants of concern.

Fig. 1.

Influence of SARS CoV-2 infection characteristics on disease control efforts. The (A) relationship between the Ct value and relative infectivity for the time prior to peak infectivity (solid line) and the time following peak infectivity (dashed line) for which Ct values greater than 40 were determined from a linear extrapolation, (B) infectivity over the disease time course, (C) the relationship between the relative infectivity and the RT-PCR diagnostic sensitivity for the time prior to peak infectivity (solid line) and the time following peak infectivity (dashed line), (D) temporal rapid antigen test diagnostic sensitivity, and (E) probability of post-quarantine transmission for an individual infected with an original strain of SARS-CoV-2 who has not been vaccinated (blue) and who has received two vaccine doses (orange). The (F) infectivity over the disease time course for original SARS-CoV-2 strain (green dotted) and the Alpha (orange dashed), Delta (purple dash dot), and Omicron (pink solid) variants. For a case infected by Omicron with no vaccination (gray dashed), 100% uptake of two vaccine doses and 0%, 30%, 70%, and 100% boosting, the (G) probability of post-quarantine transmission for quarantine durations from 0 to 14 d with a rapid antigen test on exit, and (H) the effective reproduction number (R_E > 1: red, R_E < 1: green, and R_E = 1: black line) for no testing and for testing frequencies from every day to every 14 d.

Fig. 2.

Optimal quarantine and serial testing strategies using a rapid antigen test for four SARS CoV-2 variants. The minimum quarantine duration with a rapid antigen test on exit that provides equivalent or lower probability of post-quarantine transmission than a 7-d quarantine with a rapid antigen test for the original strain in an immunologically naive population (gray dotted), for (A) up to 100% two-dose uptake, and for (B) 100% two-dose uptake plus 0% to 100% booster uptake for the original strain(s) (green dotted), as well as Alpha (orange dashed), Delta (purple dash–dotted), and Omicron variants of concern (pink solid). The minimum frequency of serial rapid antigen testing to obtain an effective reproduction number (R_E) below one with (C) 0% to 100% two-dose uptake and (D) with 100% two-dose uptake plus 0% to 100% booster uptake. When daily testing was determined to be insufficient to suppress an outbreak (i.e. R_E ≥ 1; only occurring with serial testing for Omicron), the minimum frequency of testing line was plotted level at the top of the y axis.