# Safety guideline for COVID-19: Role of prevalence of infection | Summary and Q&A

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April 8, 2021
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MIT OpenCourseWare
Safety guideline for COVID-19: Role of prevalence of infection

## TL;DR

Safety guidelines for controlling the spread of a pandemic should consider both the indoor reproductive number and the prevalence of infection in a given region.

## Key Insights

• ⚾ Safety guidelines based on the indoor reproductive number alone are conservative and help limit the spread of the disease at a population level.
• 🥡 The prevalence of infection in a region should be taken into account to determine appropriate restrictions.
• 🤵 The model assumes independent and random transmission events in a well-mixed room.
• #️⃣ The number of infected individuals is modeled using a binomial distribution, reflecting the statistical representation of the population.
• ☠️ The transmission rate can be calculated using the number of infected and susceptible individuals in the room.
• #️⃣ The expected value of the number of transmissions depends on the prevalence of infection, number of susceptible individuals, and the overall number of people in the room.
• ⚾ Calculations are based on assumptions of independent transmission events and uncorrelated infected individuals and transmissions.

## Transcript

PROFESSOR: So until now, we based the safety guideline on the indoor reproductive number, which is essentially the effective number of new infections from a single infected person or per infected person in the room. And in many cases, that is the right variable to think about. In fact, it's essentially the most conservative definition that allows u... Read More

### Q: What is the significance of considering the prevalence of infection in safety guidelines?

Considering the prevalence of infection helps determine the appropriate level of restrictions in a given region. As the number of infected individuals in the population increases, stricter measures should be implemented to control the spread of the disease.

### Q: How is the transmission rate calculated in the model?

The transmission rate is calculated by multiplying the number of infected individuals (I) by the number of susceptible individuals (S) in the room. This rate is influenced by the prevalence of infection (pI) and the probability of transmission (TMN).

### Q: What assumptions are made in the model for random transmissions?

The model assumes that the transmission events are independent and identically distributed Poisson processes. It neglects any correlations between the infected individuals and assumes that the number of infected people and transmission events are uncorrelated.

### Q: How is the expected number of transmissions calculated?

The expected number of transmissions is calculated by multiplying the total number of pairs of infected and susceptible individuals (IS) by the expected value of the transmission time (tau MN). This can be further simplified using the average transmission rate (beta bar) and the physical parameters of the room.

## Summary & Key Takeaways

• Safety guidelines have traditionally been based on the indoor reproductive number, which measures the effective number of new infections from a single infected person in a room.

• The prevalence of infection in a region should also be taken into account when determining safety restrictions.

• A simple model based on random transmissions and the number of infected and susceptible individuals helps calculate the expected number of transmissions in a room.