As vaccine rollout begins to reach clinically effective levels in many countries, the question of reopening public entertainment facilities has become a burning one. However, this step must include considered policies on how to safeguard public health as well as open up public spaces.
A new preprint research paper provides some insights into how this may be done using computational modeling. The study, which appeared on the medRxiv* server, deals with the mitigation strategies that must be implemented in order to contain the virus.
Existing protocols include restricting the number of visitors, more frequent and intensive cleaning, the mandatory wearing of masks, the use of personal protective equipment (PPE) by park staff, entry temperature checks, and hand sanitization on a routine basis.
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
Study aims and details
The current study used simulations to understand how infected surfaces could cause indirect viral spread, besides direct spread, in a theme park setting. The parameters used include hygiene, cleaning routines, social distancing, and the use of PPE, with temperature checks at the gate.
The researchers used an approach called multi-patch modeling. This method divided the park into different patches containing both workers and visitors, with varying disease status (such as susceptible, presymptomatic infected, asymptomatic infected, symptomatic infected, and recovered); vaccinated; with PPE-wearing visitors and non-compliant visitors. Patches were also categorized into locations where queues form and rides are used as the sites of direct and indirect transmission.
The model simulates viral spread and shedding from infected persons, providing a dynamic picture of the entire park with all the above components. Some assumptions are made, such as the low probability that symptomatic visitors would stay long in the park and that frequent cleaning will be done, including at the end of the day.
What were the results?
The study shows that the two most important measures are compliance with PPE use by staff and increased cleaning. The latter has a more significant impact on the number of secondary infections in the park. However, with cleaning costs being an important factor, the feasibility of cleaning every 2 or 4 hours must be considered and compared with that of providing PPE for staff as required.
Neither of these measures will affect the progression of the disease, obviously. The basic viral reproduction number R0 is affected by the rate of viral shedding, while control reproduction number, Rc, is also influenced by the effectiveness of PPE to restrict viral contamination of the environment by humans.
Once-daily cleaning is acceptable to reduce the number of secondary infections occurring in the park if the rate of viral shedding and the fraction of visitors are low, provided PPE compliance is high. This should apply even to recovered and vaccinated individuals until the duration of immunity is determined.
With higher numbers of visitors, the fraction of PPE compliance by visitors becomes insignificant, and the frequency of cleaning takes on great importance. Staff-visitor interactions are typically short at such sites, and this was found to be insignificant in reducing new infections.
Instead, viral shedding is a more useful predictor of the probability of new infection, explaining why cleaning rates are more important than visitor-worker contacts.
“Here, we see that reductions in the number of hours between cleanings are needed to significantly reduce the number of A infections produced over the course of one park day.”
The greater the number of infected visitors, the more significant the cleaning frequency becomes.
If the virus becomes more transmissible, by 1.5 times, there is no change in the number of new infections at low or medium levels of infected visitors, provided the park is cleaned once a day. But if cleaning is done more frequently than this, the number of secondary infections at the park changes by order of magnitude, depending on the virus shedding rate and the fraction of visitors.
What are the implications?
Measures to reduce the risk of infection at theme parks include minimizing virus shedding by excluding known infected visitors, reducing the number of visitors, encouraging PPE compliance, and using effective PPE for workers.
However, the rate of cleaning is seen to be the most important predictor of the number of new infections in this setting, and it becomes crucial as the number of visitors goes up. With the proper use of masks and hand sanitization, a low-visitor theme park can get by with once-a-day cleaning.
Such findings will help develop appropriate plans to prevent fresh outbreaks stemming from such public spaces. However, cost-benefit assessments are lacking in this study and must be undertaken before any strategy can be described as optimal. The aim is to reduce both viral transmission and park maintenance costs.
The researchers are working on a refinement of this model, using agent-based modeling that will include the park's structure with different indoor and outdoor rides and the movements of the various people in the park. Such studies will add to the utility of this work.
*Important notice: medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.
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