Serial interval and transmission dynamics during the SARS-CoV-2 Delta variant predominance in South Korea

Abstract

We estimated the mean serial interval and superspreading potential for the Delta variant SARS-CoV-2. As the Delta variant increased in prevalence, the mean serial interval declined from 4.0 to 2.5 days. However, the risk of superspreading events was similar, as 25% to 27% of cases seeded 80% of all transmissions.

Understanding how fast SARS-CoV-2 variants transmit from household studies

“…The mean household generation time for the delta variant is clearly shorter than that of its ancestral strains (4·0–5·2) 8 and is similar to another estimate of 2·9 days (2·4–3·3) for the delta variant in a non-household study in China. 4 The authors estimated a mean household serial interval of 1·8 days (95% CI 1·0–2·4) for the delta variant, which is consistent with estimates of 2·0–2·5 days in Asian countries 4 , 6 , 7 and is substantially shorter than the 3·5 days (2·7–4·1) estimated for the alpha variant. A proportionally larger decrease in the household serial interval (48·6%) than the household generation time (28%, 95% CI 0–48%) for the delta variant compared with the alpha variant is most likely a consequence of the delta variant's slightly longer (7·8%) presymptomatic infectious period and its higher relative transmissibility (39·3% higher) during this period (calculated on the basis of information in appendix 2 p 24 of the Article from Hart and colleagues).…”

“…Only a few studies have estimated generation times directly for these variants from contact-tracing data. 4 Although some studies estimated the serial interval for variants of concern, 6 this interval cannot reliably approximate the generation time for SARS-CoV-2 because of its presymptomatic transmissibility.…”

SARS-CoV-2 variant dynamics across US states show consistent differences in effective reproduction numbers

“…We parameterize all variants excluding Delta and Omicron as having generation time g as having Gamma distribution with mean 5.2 and standard deviation 1.2 in line with the estimates of [25]. Due to observed shorter serial intervals for Delta and Omicron, we instead use a mean generation time of 3.6 for Delta and a mean of 3.2 for Omicron [26][27][28]. For all variants, we parameterize the onset time o as having LogNormal with mean 6.8 and standard deviation 2.0 in line with [29].…”

An assessment of transmission dynamics via time-varying reproduction number of the second wave of the COVID-19 epidemic in Fiji

“…The serial interval distribution is the most crucial assumption to make. Ryu et al [35] investigated the serial interval and transmission dynamics during SARS-CoV-2 Delta variant predominance in South Korea, and reported the estimated mean and standard deviation of the serial interval distribution.…”

“…For this study, we assumed a discrete gamma-distributed SI for SARS-CoV-2 with mean of 3.6 days and a standard deviation (s.d.) of 4.9 days following the reported results of [35]. Furthermore, we used the findings of a recent research by Imai et al [36] for the basic reproduction number ( R 0 ), which was calculated using data from the early stages of the COVID-19 epidemic in Wuhan.…”