URL

https://www.medrxiv.org/content/10.1101/2020.12.09.20246538v1

Type d’article

Preprint

Thème

Stratégies de contrôle Immunité

Que retenir de cet article, en 1-2 phrases ?

Using a compartmental ODE model, parameterized by the COVID-19 case numbers from Mexico, the authors examine the effect of different vaccination scenarios on the epidemic dynamics. The authors find that fast vaccination of a significant fraction of the population (~30% within 4 months) can have the same effect as general mobility restrictions.

Objectifs de l’étude / Questions abordées

Study the effect of vaccination on the epidemic dynamics of COVID-19 in a (spatially) structured population.

Méthode

The authors use an ODE model with different compartments for susceptible, vaccinated, exposed, symptomatically infected, asymptomatically infected, reported and recovered cases in a three-patch metapopulation. Epidemiological parameters are informed by estimates for Mexico.
The three patches reflect locations with a low, intermediate and high risk of infection. Parameters related to vaccination are varied. In total, nine scenarios are studied: three different times to reach the target coverage of vaccination in the population (1 month, 3 months, 5 months) are considered and combined with three different scenarios for the epidemiological effect of the vaccine (pessimistic, intermediate, optimistic), where the vaccine efficacy, fraction of the population receiving the vaccine and duration of vaccine-acquired immunity are varied.

Résultats principaux

  • The longer the time that individuals spend in high-risk patches, the higher the overall number of infections throughout the whole meta-population. Still, a prioritization of vaccinations in the high-risk patch does not reduce the number of total infections by much. This is most likely due to the choice of population distribution over the patches (50% in low-risk patches, 30% in intermediate-risk patches, 20% in high-risk patches). The conclusion is that individuals in high-risk areas do not necessarily need to receive the vaccine first to reduce the overall epidemic burden by a noticeable amount.
  • The authors also compare the effect of vaccination to the impact of restricted mobility where people spend 80% of their time in their corresponding patches. Within the studied parameter settings, only a fast vaccination campaign (2 months to reach 30% coverage) results in a reduced epidemic burden in the metapopulation when compared to the reduced mobility scenario. Other variations, such as vaccine efficacy or coverage do not contain the epidemic as much as the reduced mobility strategy that is studied.
  • If during the first half of 2021, a fraction between 20-50% of the population is vaccinated, the number of cases in Mexico could potentially be reduced by 30-50% by the end of 2021 when compared to the no-vaccine scenario.

Commentaire / brève évaluation, limites, ouvertures possibles

Interesting study that assesses the impact of different vaccination scenarios on the epidemic dynamics.
The authors could have explored (numerically) the herd immunity threshold in their framework because this would be an important information for policy making.