Risk of Secondary Infection Waves of COVID-19 in an Insular Region: The Case of the Balearic Islands, Spain

  1. Víctor M. Eguíluz
  2. Juan Fernández-Gracia
  3. Jorge P. Rodríguez
  4. Juan M. Pericàs
  5. Carlos Melián

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Abstract

The Spanish government declared the lockdown on March 14th, 2020 to tackle the fast-spreading of COVID-19. As a consequence, the Balearic Islands remained almost fully isolated due to the closing of airports and ports, these isolation measures and the home-based confinement have led to a low prevalence of COVID-19 in this region. We propose a compartmental model for the spread of COVID-19 including five compartments (Susceptible, Exposed, Presymptomatic Infective, Diseased, and Recovered), and the mobility between municipalities. The model parameters are calibrated with the temporal series of confirmed cases provided by the Spanish Ministry of Health. After calibration, the proposed model captures the trend of the official confirmed cases before and after the lockdown. We show that the estimated number of cases depends strongly on the initial dates of the local outbreak onset and the number of imported cases before the lockdown. Our estimations indicate that the population has not reached the level of herd immunization necessary to prevent future outbreaks. While the low prevalence, in comparison to mainland Spain, has prevented the saturation of the health system, this low prevalence translates into low immunization rates, therefore facilitating the propagation of new outbreaks that could lead to secondary waves of COVID-19 in the region. These findings warn about scenarios regarding after-lockdown-policies and the risk of second outbreaks, emphasize the need for widespread testing, and could potentially be extrapolated to other insular and continental regions.

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  1. Version published to 10.3389/fmed.2020.563455
  2. ScreenIT

    SciScore for 10.1101/2020.05.03.20089623: (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

    No key resources detected.

    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:
    The model also has several limitations. First, as it is constructed for fitting the global numbers of infected patients, it is missing finer structure, needed for the evaluation of risks of subpopulations that are differently exposed to the virus or have different outcomes, such as the population of elderly people or health workers. Second, for COVID-19 there is evidence of three main transmission channels, namely direct contact with an infected individual with symptoms (14), contacts with an asymptomatic individual (24, 25), and environmental transmission (26). The present model takes into account the first two modes of transmission, but not the environmental one explicitly, although probably the fitting has assigned part of this transmission to the processes included in our model. Therefore, there is not a direct way of measuring the effect of interventions to reduce environmental transmission. Third, the model also considers asymptomatic and symptomatic individuals to be infectious in the same way, although the viral shedding in asymptomatic individuals is indeed lower (5). This can have a mild impact on the number of infected individuals that the model predicts. Fourth, the model assumes that the mobility restrictions are applied in the same way to all of the agents in the system and thus is lacking the fact that symptomatic infected individuals will modify their mobility drastically, either if they are quarantined at home or admitted to a hospital. We are therefore overe...

    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: Please consider improving the rainbow (“jet”) colormap(s) used on page 30. At least one figure is not accessible to readers with colorblindness and/or is not true to the data, i.e. not perceptually uniform.

    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.

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  3. Version published to 10.1101/2020.05.03.20089623v1 on medRxiv