[nudephil (OP)]

Here's a question from Liz:

Why do some people who have been in close contact with a symptomatic COVID-19 positive person NOT develop the disease themselves?

We lived for 3 days with my daughter's partner, who developed symptoms on the last day with us. She subsequently tested positive on her serological blood test. Neither my daughter, husband, or myself developed symptoms, despite the close contact with her during the stay. Both my husband and myself have tested negative on our serological blood tests. 

My younger daughter is now back at university and many of her student friends report cases of one person showing symptoms and testing positive, but others in the same household not succumbing to the disease despite living with them.

Is work being carried out to look at possible protective mechanisms? Or is it due to the mechanism of spread?

What's the current thinking?

[evan_au]

The current thinking is that there are many asymptomatic cases.
- There may also be some rare genetic variants that prevent the virus from docking with the ACE2 receptor. But this is likely to be a minority of cases.

If your family now does a serology test, you could tell if you were infected, but have now developed an immunity.
- But don't leave it too long for the test, as antibody levels start to decline a few weeks after initial exposure.

[set fair]

There are several possible reasons

The body shakes off the infection quickly, either with the innate immune system or T cell immunity, without making antibodies.

Cross immunity eg from another coronavirus

Innate immunity, I think unproven