Basic Reproduction Number (R0): The average number of secondary cases produced by a single infected case in an otherwise susceptible population.

Case fatality ratio (CFR): The proportion of detected cases of a given disease that die as a result of it.

Cluster: An aggregation of cases grouped in place and time that are suspected to be greater than the number expected, even though the expected number may not be known.

Effective Reproduction Number: The average number of secondary cases arising from an infected case, with a given level of immunity in the population.

Endemic: Refers to the constant presence, and/or usual prevalence of an infectious disease in a population within a geographic area. The amount of a particular disease that is usually present in a community is referred to as the baseline or endemic level of the disease.

Epidemic: The occurrence of disease cases in excess of normal expectancy, usually referring to a larger geographical area than "outbreak".

Exposed: A contact between a susceptible and infected person that could potentially lead to infection.

Fatality Rate of Infections (FRI): The proportion of overall infections that die as a result of it.

Incidence: The number of new infections during a given interval of time (for example, weekly incidence).

Incubation period: Period between exposure and onset of clinical symptoms.

**Infectious period: **The length of time for which an infected individual is infectious to others.

Latent period: Period between exposure and ability to transmit to others.

Outbreak: The occurrence of disease cases in excess of normal expectancy, usually referring to a smaller geographical area than "epidemic".

Pandemic: An epidemic that has spread over several countries or continents, usually affecting a large number of individuals.

Pathogen: A micro-organism which can cause, or causes disease or damage to a host.

Prevalence: The number of infected people in a population at a given point in time.

• Case Numbers building up fast
• China numbers are in decline, but doubts remain if that will stay low after draconian measures are lifted.
• Most countries are still in contain phase.
• Two choices, go with WHO advise and lock down all to mitigate the virus such as with China. Alternative, mitigate with measures protecting the most vunlerable and herd immunity.

• Deaths vs Cases analysis tells us little because it takes a long time from diagnoses to understanding if they will survive or not.
• 10% or less of all infections are being detected in China (the top of the pyramid)
• 25% global detection rate
• 'We estimate 50,000' new infections a day in China, and rising.
• Limited evidence of it slowing but will peak in about one months time.
• Forward projections are the infection is doubling every few days.

Statistical Analysis

• Statistical analysis is noisy and hard to use.
• We aim to ask: how transmissible is the new pathogen, how long has it been trasmitting, how large is it, how severe is it.
• Uncertainty ranges are always high early, incubation period and other things are hard to estimate. Every case generates 2.6 (with a range of 2.1 up to 3)
• Generally policy makers want everything to be certain, but our uncertainty range tells them how confident we are.

Interventions

• Vaccine could take months/years.
• Limited options
• Testing of anti-viral treatments to see if they work in these cases
• public intervention, identifying early (such as we did with SARS), this is unsure if it will be effective.
• If people with mild symptoms continue to transmit: it may be hard to stop.

Reasonable Wost Case Scenario

The numbers are really hard to estimate, for now fatality rate is 1% to 4%: this high range allows government to establish a level of impact, book beds, ventilators and so on. 25% and 40% of the population to be sick in the first year. 20% don't show symptoms so total 60% in the first year. This informs the worst case ratio.

• Case numbers are declining in Wuhan, reduced by measures which will be helping.
• Nationally China is reducing in the official statistics.
• Critical will be next few weeks as they close schools.
• Japan and Singapore may be of concern: we expect Japan to be ahead of other countries.
• This period is waiting to see.
• Get a hand on the drugs that China have tried
• China needs to share the data quickly
• Non pharamceutical interventions: change peoples behaviours.

• UK in containment mode
• Focusing on Non pharamceutical interventions

Crucial to make good analysis, and manage our new connected world. Experts at the JIDAH are providing support and info to WHO and other organisations. Trying to help with planning and metrics.

Key concerns

• How many people are infected
• How to reduce

We noticed that the cases in Wuhan (the epicenter of the outbreak) were under reported, because the crucial clue was at the time of first detections, cases were being detected in Thailand and Japan.
If we know the volume of travel from Wuhan to these countries we can then infer how many cases there are in Wuhan.

This is how it was estimated there were 1700 instances of the virus in 17th of January compared to the 50 cases.

It's not the behaviour of anyone person that is important. It is the average behaviour of the virus that matters. For an there to be an epidemic, R0 has to be greater than 1

R0 means the basic reproductive number : the *average number of secondary infections generated by one individual.

Estimating this is critical as it determines how strong interventions should be.

• Coronavirus: 2.9
• Flu: 1.5
• Polio : 6

SARS was easier because people were only infectious, we don't know if Coronavirus transmits silently i.e. before symptoms present themselves.

Impact of non-pharmaceutical interventions

Estimates of the basic reproduction number