Yale Immunology prof answers questions, such as "Will summer save us?" Very informative...
[Here are some excerpts. There is a lot more, all of it interesting. The last paragraph that I posted suggests that social distancing over time--I would imagine a long time--makes the virus adapt to become less virulent.]
http://nautil.us/issue/84/outbreak/summer-wont-save-us-from-covid_19
What role did winter play in the spread of the pandemic?
Winter definitely plays a role because we know, by studying many other respiratory pathogens, that the winter months provide an ideal situation for viruses to transmit in the air. If you look at the influenza virus, the peak is in winter. Part of the reason for this is because we have low humidity indoors during winter, and that is an ideal condition for the virus to survive in the air. Another part is the fact that our defense against respiratory viruses declines in low-humidity settings. These things usually contribute to infection and transmission of influenza and other respiratory viruses.
Why does low humidity help the virus spread?
What happens when you cough or sneeze is that you expel the virus particle inside these droplets. When the droplet hits the air, and it’s very dry, it loses the water content and it becomes desiccated. Little dried particles float in the air, and they tend to persist in the air for hours. Whereas if the humidity is high, those droplets acquire water vapor from the air, and they become larger and they drop on the floor instead of infecting someone else. The low humidity basically allows these aerosolized particles to remain in the air for much longer because they don’t retain the water very well.
Did another winter factor come into play?
Likely sunlight, because it’s important to metabolize vitamin D. In the winter, people tend to stay indoors more often and they’re not getting enough sunlight. Vitamin D is well known to boost the immune system. That’s another winter factor that might affect the person’s ability to defend against the respiratory infection.
We’re not even at the peak of it. We are just bracing.
Will summer save us?
No, this doesn’t mean summertime will basically cure the virus. The aerosol transmission will likely reduce in the summer, but the direct transmission—as well as fomite transmission through things like skin cells and clothes—is still going to happen.
What sets this virus apart from common cold coronaviruses?
Definitely this virus is more virulent, more lethal. You don’t really die of the common cold, but this virus kills. The other difference is it seems we don’t have any prior immune response to this version of the coronavirus, so nobody has resistance. Whereas with the common cold, most of us have been exposed multiple times—we have antibodies and T-cell response, so the disease is much milder. This virus also has a very long incubation period. You might be infectious but you don’t know, because you don’t have any symptoms. That makes this virus very contagious, with the ability to spread well among humans. The key gap in the field is to try to understand what type of immune response is protective. We still don’t know exactly what we’re even aiming for with a vaccine. We don’t know which type of antibody responses confer protection versus which type will trigger worse disease. Similar for T-cell response, and so on. These are insights needed for therapy and vaccine strategies.
How does a novel coronavirus differ from viruses that have been with us for a long time?
If you look at pandemic viruses that emerge as human-to-human transmission for the first time, they tend to be quite virulent, at least the ones that we understand, we know of. When a pandemic flu, or this COVID-19, first emerge in humans and start transmitting, they tend to have quite high virulence. What happens is that the virus will eventually be selected for its ability to replicate and transmit. Those features might be in conflict with virulence because if a virus makes you so sick that you’re not going out of the house and infecting other people, then the success of the virus dies right there. For viruses that have been circulating for many years, like the rhinovirus, you usually don’t get so sick to a point where you stay home and don’t interact with anyone. That sort of makes these viruses much more successful than if a virus were to kill you immediately. There’s a balance that the virus has to strike to become successful. Over the years, usually the virus that’s circulating in humans tends to have less virulence so that people go out, infect others. I’m not sure whether that’s going to happen to this particular virus.
= new reply since forum marked as read
at certain latitudes the rates of infection are consistently lower.
Think of it as a brake.
When you brake you don't suddenly stop. Most of the time you don't even stop. You slow down a bit. (Unless you're in Los Angeles, Manhatten, or I-45 in Houston, then since you never get moving fast "slow down a bit" = "stop."
So the interviewer asked if summer will stop the virus. Answer: "No." But the epidemiologist continued to say that transmission will be reduced. Then he points out ways it might still be transmitted--direct contact and fomites. (Although that last hasn't been demonstrated yet, as far as a I know). And, of course, it will still be transmitted by aerosols and droplets.
It's the same conceptual problem that many had with saying that younger people were "at lower risk." Many assumed it was all or nothing, and if they weren't "at (special) risk" it meant they were "at no risk."
