Correct me if I am wrong. You don't test positive for COVID. You test for the SARS2 Corona Virus. COVID is the disease you get from it. You can get the Corona Virus and feel pretty much nothing. Or you can get sick, real sick or die. The Vaccine doesn't put up some kinda force field around you killing the Virus before it gets into you. It attacks the Virus when it does. You might feel a little poorly for awhile while the attack is going on. And you can test positive for the Virus while this is happening.
Correct. It's not a force field. The virus may still land on the cells that line your airways. The only way for us to tell whether virus replication happens in a individual is by detecting
- an antigen on the surface of the virus using a antigen test
- the virus genetic material using RT-PCR
- the virus by its effect in a cell culture
- in a previously seronegative patient, the creation of antibodies in that patient (seroconversion)
All these tests have a lower detection limit. So even with RT-PCR, a person may have fought off the virus on the cells that cover their airways but we just happen to not catch that phase or we are below the detection limit of the test.
The estimate is that with the delta variant, the number of individuals in a group who test positive is decreased by 60%. The effect of the vaccine on infectivity is less well documented. It was doing that extremely well for the variant prevalent in Israel during their vaccine campaign, it appears to be much less effective for the delta variant.
What we do know is that the vaccine, even for the delta variant, drastically reduces the number of individuals who get covid pneumonia, pulmonary embolism, stroke and multiorgan failure. Almost all of the younger breakthrough cases have mild disease and don't require hospitalization (in between it kills a few, but that's just math at work). The breakthrough cases that result in hospitalization tend to be in older individuals who got the vaccine early.