Thread by @GertrudRey

UPDATE ON SARS-COV-2 (the virus that causes COVID-19)

I provide here a bullet point summary of today’s episode of #twiv. I would encourage you to listen to the whole episode yourself! The link is below. (1/18)

microbe.tv/twiv/twiv-591/

•Incubation period is on average 5-7 days.
•83% of infections are mild.
•There is no question that there are asymptomatic infections and undetected networks of transmission chains. (2/18)

The numbers of infections worldwide that we know about today (162,687, the second I type this) only represents the number of people that have been tested, but the number of people actually infected (the denominator) is estimated to be much, much higher. (3/18)

The reason the denominator is thought to be higher is in part because of asymptomatic infections. This is good news, because once we have a better idea of what the denominator is, the mortality rate will drop significantly. (4/18)

The number of people one infected person can potentially infect (the R0 number) is estimated to be between 2.5 and 3.2. For comparison, the R0 for flu is around 2 and for measles it is 12-18. (5/18)

What is droplet transmission and how does it differ from aerosol? What does “airborne” mean and is SARS-CoV-2 airborne?
•Droplets are large and are only briefly airborne. Because of their weight, they don’t stay suspended in the air for very long and tend to drop... (6/18)

...(on the floor or on nearby objects) in the vicinity of the person who coughed or sneezed them out. Aerosol particles are smaller and lighter and are suspended in the air longer, travel larger distances. (7/18)

There is currently no evidence to suggest that SARS-CoV-2 is transmitted by these “airborne” aerosol particles. It is spread by large droplets. That is the current scientific consensus. (8/18)

Why don’t children get sick and are they actually infected? Yes, kids are infected and produce very high viral levels. This alone is a good reason to close schools in order to slow down the spread. However, we don’t know why they don’t show symptoms. (9/18)

How do we quash this pandemic? At this point the pandemic will likely only end when the population has acquired sufficient herd immunity. Herd immunity is protection from infectious disease that occurs when a large percentage of a population (~70%) has become immune. (10/18)

This will cause the virus to “burn out” or only replicate in individuals without causing symptoms. We can dampen the transmission rate of the virus and reduce the number of infections by taking measures such as closing schools, large events, and working from home. (11/18)

But ultimately, extinction of the virus will require herd immunity of about 70%. How do we achieve herd immunity? Through natural infection or vaccination. Vaccination would be the preferred route. But, as of now we don’t have a vaccine. (12/18)

Sunlight (UV rays), warm temperatures, and humidity all reduce the viability of virus on surfaces. On that note, warmer weather should reduce rates of transmission, but they won’t eliminate the virus entirely. (13/18)

The virus will continue to spread in human populations, even during the summer (like influenza during the summer at lower levels). It is likely that the COMBINATION of warmer weather and increasing herd immunity in the population will reduce transmission in the summer. (14/18)

Based on evidence from other respiratory viruses it is likely that we are facing a 1-3 year pandemic until we have achieved sufficient herd immunity. (15/18)

On the topic of vaccines… There are at least two major vaccine candidates that are moving rapidly towards Phase I Clinical Trials (assessing safety). (16/18)

If either one is considered safe, it still has to undergo Phase II (assessing efficacy) and Phase III trials (randomized testing using controls) before it is licensed by the FDA for use in this country. (17/18)

The prospect of an FDA-approved vaccine for this virus in an 18-month time frame is highly optimistic. (18/18)