Serial Intervals and Incubation Periods of SARS-CoV-2 Omicron and Delta Variants, Singapore

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Abstract

We compared serial intervals and incubation periods for SARS-CoV-2 Omicron BA.1 and BA.2 subvariants and Delta variants in Singapore. Median incubation period was 3 days for BA.1 versus 4 days for Delta. Serial interval was 2 days for BA.1 and 3 days for BA.2 but 4 days for Delta.

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Most cited references 6

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Investigation of three clusters of COVID-19 in Singapore: implications for surveillance and response measures

Rachael Pung, Calvin J. Chiew, Barnaby E Young … (2020)

Summary Background Three clusters of coronavirus disease 2019 (COVID-19) linked to a tour group from China, a company conference, and a church were identified in Singapore in February, 2020. Methods We gathered epidemiological and clinical data from individuals with confirmed COVID-19, via interviews and inpatient medical records, and we did field investigations to assess interactions and possible modes of transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Open source reports were obtained for overseas cases. We reported the median (IQR) incubation period of SARS-CoV-2. Findings As of Feb 15, 2020, 36 cases of COVID-19 were linked epidemiologically to the first three clusters of circumscribed local transmission in Singapore. 425 close contacts were quarantined. Direct or prolonged close contact was reported among affected individuals, although indirect transmission (eg, via fomites and shared food) could not be excluded. The median incubation period of SARS-CoV-2 was 4 days (IQR 3–6). The serial interval between transmission pairs ranged between 3 days and 8 days. Interpretation SARS-CoV-2 is transmissible in community settings, and local clusters of COVID-19 are expected in countries with high travel volume from China before the lockdown of Wuhan and institution of travel restrictions. Enhanced surveillance and contact tracing is essential to minimise the risk of widespread transmission in the community. Funding None.

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Outbreak caused by the SARS-CoV-2 Omicron variant in Norway, November to December 2021

Lin T Brandal, Emily MacDonald, Lamprini Veneti … (2021)

In late November 2021, an outbreak of Omicron SARS-CoV-2 following a Christmas party with 117 attendees was detected in Oslo, Norway. We observed an attack rate of 74% and most cases developed symptoms. As at 13 December, none have been hospitalised. Most participants were 30–50 years old. Ninety-six percent of them were fully vaccinated. These findings corroborate reports that the Omicron variant may be more transmissible, and that vaccination may be less effective in preventing infection compared with Delta.

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Serial intervals of respiratory infectious diseases: a systematic review and analysis.

Margaretha Vink, Martinus Christoffel Jozef Bootsma, Jacco Wallinga (2014)

The serial interval of an infectious disease represents the duration between symptom onset of a primary case and symptom onset of its secondary cases. A good evidence base for such values is essential, because they allow investigators to identify epidemiologic links between cases and serve as an important parameter in epidemic transmission models used to design infection control strategies. We reviewed the literature for available data sets containing serial intervals and for reported values of serial intervals. We were able to collect data on outbreaks within households, which we reanalyzed to infer a mean serial interval using a common statistical method. We estimated the mean serial intervals for influenza A(H3N2) (2.2 days), pandemic influenza A(H1N1)pdm09 (2.8 days), respiratory syncytial virus (7.5 days), measles (11.7 days), varicella (14.0 days), smallpox (17.7 days), mumps (18.0 days), rubella (18.3 days), and pertussis (22.8 days). For varicella, we found an evidence-based value that deviates substantially from the 21 days commonly used in transmission models. This value of the serial interval for pertussis is, to the best of our knowledge, the first that is based on observations. Our review reveals that, for most infectious diseases, there is very limited evidence to support the serial intervals that are often cited.

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Author and article information

Journal

Journal ID (nlm-ta): Emerg Infect Dis

Journal ID (iso-abbrev): Emerg Infect Dis

Journal ID (publisher-id): EID

Title: Emerging Infectious Diseases

Publisher: Centers for Disease Control and Prevention

ISSN (Print): 1080-6040

ISSN (Electronic): 1080-6059

Publication date (Print): April 2023

Volume: 29

Issue: 4

Pages: 814-817

Affiliations

[1]National Centre for Infectious Diseases, Singapore (K. Zeng, Santhya, A. Soong, M. Chen I-Cheng);

[2]Ministry of Health, Singapore (K. Zeng, N .Malhotra, D. Pushparajah, Z.J.M. Ho, M.C. I-Cheng);

[3]KK Women's and Children’s Hospital, Singapore (K.C. Thoon);

[4]National University of Singapore, Singapore (K.C. Thoon);

[5]National Technological University, Singapore (K.C. Thoon);

[6]National Public Health Laboratory, Singapore (B. Yeo)

Author notes

Address for correspondence: Mark Chen I-Cheng, National Public Health and Epidemiology Unit, National Centre for Infectious Diseases, 16 Jln Tan Tock Seng, 308442, Singapore; email: mark_ic_chen@ 123456ncid.sg

Article

Publisher ID: 22-0854

DOI: 10.3201/eid2904.220854

PMC ID: 10045676

PubMed ID: 36878009

SO-VID: b82f3933-08b3-403f-a508-b7256813a1d7

License:

Emerging Infectious Diseases is a publication of the U.S. Government. This publication is in the public domain and is therefore without copyright. All text from this work may be reprinted freely. Use of these materials should be properly cited.

Serial Intervals and Incubation Periods of SARS-CoV-2 Omicron and Delta Variants, Singapore

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Novel Coronavirus Disease COVID-19

Most cited references 6

Investigation of three clusters of COVID-19 in Singapore: implications for surveillance and response measures

Outbreak caused by the SARS-CoV-2 Omicron variant in Norway, November to December 2021

Serial intervals of respiratory infectious diseases: a systematic review and analysis.

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