Shorter Incubation Period among Unvaccinated Delta Variant Coronavirus Disease 2019 Patients in Japan.

Tsuyoshi Ogata,Yuki Takahashi,Atsushi Hirayama,Fujiko Irie,Hideo Tanaka

doi:10.3390/ijerph19031127

Tsuyoshi Ogata, Yuki Takahashi + Show 3 more

Open Access

https://doi.org/10.3390/ijerph19031127

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Abstract

Few studies have assessed incubation periods of the severe acute respiratory syndrome coronavirus 2 Delta variant. This study aimed to elucidate the transmission dynamics, especially the incubation period, for the Delta variant compared with non-Delta strains. We studied unvaccinated coronavirus disease 2019 patients with definite single exposure date from August 2020 to September 2021 in Japan. The incubation periods were calculated and compared by Mann–Whitney U test for Delta (with L452R mutation) and non-Delta cases. We estimated mean and percentiles of incubation period by fitting parametric distribution to data in the Bayesian statistical framework. We enrolled 214 patients (121 Delta and 103 non-Delta cases) with one specific date of exposure to the virus. The mean incubation period was 3.7 days and 4.9 days for Delta and non-Delta cases, respectively (p-value = 0.000). When lognormal distributions were fitted, the estimated mean incubation periods were 3.7 (95% credible interval (CI) 3.4–4.0) and 5.0 (95% CI 4.5–5.6) days for Delta and non-Delta cases, respectively. The estimated 97.5th percentile of incubation period was 6.9 (95% CI 5.9–8.0) days and 10.4 (95% CI 8.6–12.7) days for Delta and non–Delta cases, respectively. Unvaccinated Delta variant cases had shorter incubation periods than non–Delta variant cases.

Highlights

The Delta variant (Phylogenetic Assignment of Named Global Outbreak lineage designation B.1.617.2) is a lineage of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It was first identified in India in late 2020 and was classified as a variant of concern (VOC) on 11 May 2021 [1]
As of 12 October 2021, Delta variant coronavirus disease 2019 (COVID19) cases had been reported in 191 countries across all six WHO regions
The estimated mean incubation period was 5.0 days, and the estimated median incubation period was 4.6 days among non–Delta variant patients when the Lognormal distribution was fitted (Table 4 and Figure 1b)

Summary

Introduction

The Delta variant (Phylogenetic Assignment of Named Global Outbreak lineage designation B.1.617.2) is a lineage of severe acute respiratory syndrome coronavirus 2. It was first identified in India in late 2020 and was classified as a variant of concern (VOC) on 11 May 2021 [1]. This variant was associated with an estimated increase in transmissibility of 97% [2]. SARS-CoV-2 VOCs bearing the L452R spike protein mutation demonstrate increased transmissibility, infectivity, and avoidance of antibody neutralization [3]. As of 12 October 2021, Delta variant coronavirus disease 2019 (COVID19) cases had been reported in 191 countries across all six WHO regions.

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