It is important to appreciate that in epidemics we do not close schools specifically because we fear for the impact of the disease on our children. Fortunately, early data suggests that the complications of COVID-19 are not affecting children. School closures work by reducing the spread of mild illness and other disease. This boosts the general immunity of the population and makes it less likely that any epidemic will grow.The public health measures in any epidemic are aimed at slowing down both the rate of progression and ultimate size of the epidemic.
- The lower the epidemic size (number of people infected) the lower the number of people who will become ill and the lower the total mortality.
- The lower the absolute volume of circulating virus the lower the risk of viral mutation.
- The lower the epidemic size the higher the likelihood of it dying out naturally. This may be influenced by environmental factors. For example, coronavirus infections often die out in Spring with an increase in warmer and more humid weather.
- Slowing the evolution of the epidemic buys time in order to:
- develop tests to help us better understand the nature of the infection and the optimal control methods
- develop treatments to optimally manage the illness
- develop a vaccine which is ultimately one of the most effective methods of controlling epidemics of infectious disease.
In addition, the measures above may be expected to reduce other coexisting infectious illnesses (Influenza, common colds etc.). This can boost population immunity which reduces the likelihood of an epidemic taking hold.
How do we prevent infections spreading?
All infectious illness is ultimately decided by two factors:
1. Exposure risk
If we are never exposed to an infectious illness we will not catch it. We can reduce risk of exposure by:
- Isolating infectious individuals
- Closing schools, where infections tend to spread
- Hand washing
- Wearing masks
- Reducing public mixing (crowds and travel)
2. Host responses
Even if we are exposed to an illness we can reduce our likelihood of having a severe response by having a good immune system. This is important both for individuals (diet, sleep, managing stress, exercise etc.) but also for population immunity.
Immunization against Influenza does not protect against this Coronavirus, now known as COVID-19. However, if we can prevent excessive Influenza infections we will increase the immunity of both individuals and the population. This reduces the likelihood of any epidemic taking hold and is one of the reasons for advising immunization.
What influences the size of an epidemic?
In another article, we have already described the following:
- Mode of Spread
- Incubation Period
- Infectivity in the Incubation
- Individual and Population Immunity
These factors ultimately lead to a basic reproduction number R0 for each illness. This number is a measure of on average how many people are infected by an individual with the specific disease. If this number is <1 the epidemic will die (this means that on average each infected person infects slightly less than one other person). If this number is >1 the epidemic is likely to grow. Infections with higher R0 values are more likely to spread. Population measures such as isolation of infected individuals, masks, hand washing, school closures, social distancing all work by reducing the exposure risk with the intention of reducing the effective transmission below 1 but regardless as much as possible in order to give the best possible chance for the epidemic to die.