On: COVID-19—Lessons learned, challenges ahead, and reasons for optimism and concern
Date: 31 March 2020
Background: Infectious disease epidemiologist.
- Until there is a vaccine, 50-70% of the population may end up getting infected.
- Math does not look good: 60% infected -> 20% of infected need hospitalization -> 1.5% of infected may end up as fatality.
- Research indicates that immunity may be reasonably durable (if there is short-term immunity, often bodes well for long-term immunity).
- See also MedCram video on Immunity and Reinfection for a more in-depth discussion of the research.
- Fatality rate.
- Has been ratcheted down (from about 1.38% to 0.66%), as previously unconfirmed cases have been added to the denominator.
- But, unconfirmed fatalities may be left out of the numerator (and fatality rate is much more sensitive to changes in the numerator).
- Fatality rate can differ by region, driven by demographics and prevalence of underlying morbidities.
- Adjusted for age and risk factors, fatality rates will eventually look similar (as ultimately virus spreads to vulnerable parts of the population).
- In the US, may still end up being in the 1-2.5% range (many over 65, high obesity in young).
- Average transmission rate (Ro) doesn’t really tell the story (general issue with averages – see “The End of Average”).
- There may be super-spreaders and people that hardly spread.
- Transmission is likely to occur early on when people start having symptoms (level of virus found in throat at that stage has been found to be 1,000x higher than for SARS-I).
- Unclear to what extent asymptomatic people may drive transmission.
- Comorbidities and risk factors.
- Risk factors differ by country, region, city.
- In China, high prevalence of smoking (high under males, lower under females).
- Generally: hypertension, obesity, Type 2 diabetes, maybe Type 1 diabetes.
- So far not: immunosuppressed patients.
- Suppression challenges.
- Lockdown: unlikely it can be sustained over a prolonged time period (heavy economic costs).
- Healthcare system: shortage of critical care supplies and healthcare staff (getting infected).
- Mask shortage: possible solutions.
- Create larger wards with permanent staff that doesn’t leave (don’t need to throw away masks).
- Find ways to clean and re-use masks.
- Test infected healthcare workers – once they are immune, no need for a mask.
- Monthly US production capacity for N95 mask is about 23 million.
- Apparently just one NYC hospital used 2 million masks last month.
- US have tested about 800k people so far.
- Huge issues with supply chain, running out of tests (shortage of reagents).
- Vaccines and antivirals: safety and effectiveness.
- Vaccines: effectiveness may be easy to solve, but safety may be a tougher issue (previous issues with trying to develop SARS-I vaccine were safety related).
- Antivirals: very few successful antivirals have been developed over the last 50-60 years.