This is my take on where we are now. What is known and not known.
What we do know is that this pandemic is at least 10 times deadlier than any other pandemic certainly in all our life times. It is unusually infectious by air, touch and feces.
It is particularly deadly to the elderly and people with underlying medical conditions, like for instance diabetes.
Above all it has shown a horrifying capacity to overwhelm hospital services, especially ICU units, running them out of resources. It has shown a terrible propensity to run ragged medical staff, infect them and extract a disproportionate mortality on them. This is probably a combination of fatigue and high infectious load of virus.
In Northern Italy it is threatening to wipe out a generation.
Children seem to be spared.
What is uncertain is how badly children can spread the virus with subclinical or mild infections. The case mortality below age 19 years is very low, but not zero.
It is uncertain if the virus can cause prenatal infection, but it probably can.
The real uncertainty is how many subclinical and very mild infections have occurred. What we do not know is that lock downs have caused the ending and reversal of the case incidence curve. We do know that severely restrictive measures work. China at the moment is coming out the other side. They plan widespread screening to see the incidence of antibodies to Covid 19 in the community. If antibody is not present in a large segment of the population there will be another epidemic, and likely a series of them after each episode of restriction of the population. These will likely continue until a vaccine is available in quantities large enough to basically immunize the whole world.
So this is where herd immunity comes in. The best analogy is that this virus has set a nuclear reactor into melt down. Now rods are required to be inserted into the reactor to slow it down and make it safe, otherwise there is a catastrophe. In this analogy people who have been exposed to the virus and developed an immunity by warding it off without getting ill or recovering from an active infection are the "rods" in the reactor. So the more of these rods we have the less dangerous the pandemic and it will come under control
However one thing we do not know yet is how long the immunity to the virus will last. Only time will give the answer to that. Length of immunity to infection is variable. For instance immunity to measles is life long. Immunity to the Noro virus is only six weeks. One thing that worries me is that this Covid 19 is a Coronavirus like the common cold, and immunity to that is short lived. However immunity to Sars to which this virus is closely related is relatively long.
Specifically the school closing is a difficult issue. The biggest argument against it is that it could and probably would reduce the availability of medical personnel and we need all hands on deck. Keeping schools open would likely increase herd immunity. However it is my view that as the horror of this pandemic is revealed close to home, public pressure will demand school closures. The decision not to close schools has been made here in Minnesota. However many states have closed or will close schools, affecting 26 million school children so far.
Lastly we are in totally uncharted waters here. The world is facing by far the greatest crisis of our lifetimes. Epidemiologists, physicians, and politicians have now to make impossibly difficult decisions, without all the data, as this is unfolding in uncharted territory. After the dust settles, and it will, some actions taken will prove in hindsight to have been harmful, some to have no effect and others beneficial. Only time will tell and now, and after, is not time to pass judgement only learn from the experiences gained.
What would really help right now is an antiviral agent that would at least greatly reduce the number of cases that need to go on ventilators, and those needing ventilators and dialysis. 3% of cases on life support require ECMO, which is oxygenating through an artificial external membrane that also usually provides continuous dialysis. That is the absolute top of the mountain of critical care support. The other bad thing about these critically ill patients is that they seem to have to stay on life support for around three weeks most often.
Making these episodes less likely and lethal will require a reordering of the world order in the wake of this. The world is currently constituted in a way the gives an unnecessary and huge opportunity for the creation of novel infectious organisms and enormous encouragement for them to propagate.
Anyhow that is my take on all this for what it is worth.
