Modelling the impacts of public health interventions and weather on SARS-CoV-2 Omicron outbreak in Hong Kong

  1. Hsiang-Yu Yuan
  2. Jingbo Liang

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Abstract

Background

Hong Kong, has operated under a zero-Covid policy in the past few years. As a result, population immunity from natural infections has been low. The ‘fifth wave’ in Hong Kong, caused by the Omicron variant, grew substantially in February 2022 during the transition from winter into spring. The daily number of reported cases began to decline quickly in a few days after social distancing regulations were tightened and rapid antigen test (RAT) kits were largely distributed. How the non-pharmaceutical interventions (NPIs) and seasonal factors (temperature and relative humidity) could affect the spread of Omicron remains unknown.

Methods

We developed a model with stratified immunity, to incorporate antibody responses, together with changes in mobility and seasonal factors. After taking into account the detection rates of PCR test and RAT, we fitted the model to the daily number of reported cases between 1 February and 31 March, and quantified the associated effects of individual NPIs and seasonal factors on infection dynamics.

Findings

Although NPIs and vaccine boosters were critical in reducing the number of infections, temperature was associated with a larger change in transmissibility. Cold days appeared to drive Re from about 2–3 sharply to 10.6 (95%CI: 9.9–11.4). But this number reduced quickly below one a week later when the temperature got warmer. The model projected that if weather in March maintained as February’s average level, the estimated cumulative incidence could increase double to about 80% of total population.

Interpretation

Temperature should be taken into account when making public health decisions (e.g. a more relaxed (or tightened) social distancing during a warmer (or colder) season).

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  1. ScreenIT

    SciScore for 10.1101/2022.05.25.22275487: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    NIH rigor criteria are not applicable to paper type.

    Table 2: Resources

    Software and Algorithms
    SentencesResources
    Daily vaccination rates of BioNTech and CoronaVac were collected from the COVID-19 Thematic Website [
    BioNTech
    suggested: None

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    Limitations: Some limitations exist in our study. First, the study mainly focus on the disease transmissibility while not explore the impact of vaccine or seasonal factors on disease severity. Second, the number of total infections may be underestimated since the proportion of cases that are underreported is largely unknown when the testing capacity is limited. Therefore, we attempted to capture the changes in underreporting and reporting delay in our modelling. Third, model validation may be sensitive to the assumption of the protectiveness of vaccine or natural infections. Here the data used in our study were based on a published empirical study without age stratification [7]. Conclusion: A recent work has suggested a striking effect of temperature on the spread of COVID-19 [10]. Here, we found that temperature was associated with a larger impact on the transmissibility than strict public health interventions without lockdown throughout a significant outbreak in a single city. Incorporating seasonal variation in temperature can improve the accuracy of modelling of SARS-CoV-2 transmission, which helps to find a balance between normal life and low health impact.

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

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  2. Version published to 10.1101/2022.05.25.22275487v1 on medRxiv