# All vaccines and treatments in development for COVID-19, to date

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While we are waiting for scientists and health care professionals to develop a vaccine for COVID-19, another tool, more readily available, is at our disposal.

Social distancing, defined as measures taken to reduce physical contact, is the first line of defense to contain an infectious disease like COVID-19. These infections are spread when people cough, sneeze, or touch the surfaces on which the virus resides.

To help us understand the real impact of these measures, today’s infographic shows how a reduction in social exposure can theoretically contain the spread of the infection.

## Theoretical potential

The calculations used to create today’s computer graphics come from Signer Laboratory, a stem cell research laboratory located at the Moores Cancer Center at the University of California at San Diego.

Using a summation formula, we can estimate the number of new infections over a 30-day period, using three scenarios.

Scenario 5 day period 30 day period
No social distancing practiced 1 person infects 2.5 * others 406 people infected as a result
50% reduction in social exposure 1 person infects 1.25 * others 15 people infected as a result
75% reduction in social exposure 1 person infects 0.625 * others 2.5 people infected as a result

* For estimates only. It is not possible to infect only a fraction of another person.

To arrive at the figures reported above, Robert A.J. Signatory, Ph.D.and his team made a number of key assumptions.

First, they estimated the base reproduction number (R0) of COVID-19 at 2.5, a figure confirmed by recent research. This means that on average, one infected person spreads the disease to 2.5 other people.

Then they assumed that an infected individual would unknowingly spill COVID-19 over the median incubation period of five days. After this period, the individual will begin to develop symptoms, self-quarantine immediately and will no longer pose a threat.

Finally, they assumed a direct linear correlation between social interactions and R0. This means that when an infected person reduces their physical contact with others by 50%, they also spread the disease by 50% less.

## Timing is everything

Although the above figures are the result of mathematical estimates, the researchers actually studied social distance from various angles.

One study used simulations to determine the extent and timing of social distancing measures necessary to prevent a pandemic. The simulated distancing measures were as follows:

Measured Details
School closure Teachers and students spent day-to-week cycles at home rather than at school.
Increased isolation of cases By becoming symptomatic, adults (90%) and children (100%) quarantined themselves for the duration of the infection.
Absence from work Every day, a person had a 50% chance of staying at home instead of going to work.
Reduced contact with the community Each day, individuals cut their physical contact with community members in half.
Combination of the four The four measures combined.

The results, for a community of 30,000 people and an epidemic with R = 2.5, are presented below. We can define the final disease attack rate like the share of people in an at-risk population who eventually get the disease.

The results showed that when no action was taken, 65% of the population has contracted the disease. However, if a combination of the four distancing measures were implemented instead, the attack rates were as follows:

• 45% (removal begins after 4 weeks)
• 21% (removal begins after 3 weeks)
• 7% (removal begins after 2 weeks)

What is clear is that social distancing was significantly more effective when implemented with minimal delay – the final disease attack rate increased faster after the third week. These results draw a parallel with today’s computer graphics, which showed us how quickly a disease can spread.

Social distancing interventions are important because they represent the only… measure guaranteed against a new strain of influenza in the early stages of a pandemic.

Kelso, J.K., Milne, G.J. & Kelly, H., BMC Public Health 9, 117 (2009)

We come to a similar conclusion with regard to the types of distancing measures implemented. In the simulations, none of the four measures taken in isolation could have had an effect similar to that of their combination.

## We all have a role to play

As the global number of COVID-19 cases continues to increase, many governments have issued quarantine orders and travel bans.

Calculation supports these decisions – it is crucial to reduce our physical contact with others, even when we do not experience any symptoms. Studies like the one summarized above also show that taking action sooner than later can significantly reduce the spread of the infection.

The main lesson to be learned from all this? Social distancing is a powerful tool for disease control, but only if we all participate.