This paper just got published this month, and I thought it was a really good study to highlight and talk about the results.
The study: How well do vaccines protect against SARS-CoV-2 infection given different amounts of exposure? Authors looked in correctional facilities where we know a lot about how close people are to a documented exposure (cell mates vs within cell block vs no documented exposure)
The results: Vaccines (and prior infection and hybrid immunity) were very protective against infection if there was no documented exposure (HR: .36, .57, .24 for vaccination, prior infection, and hybrid) or on the same cell block (HR: .61, .69, .41 for vaccination, prior infection, and hybrid), but only lightly protective against infection if the index case was a cellmate (HR: .89, .96, .80 for vaccination, prior infection, and hybrid, and none were statistically significant)
HR, Hazard ratio, can be interpreted as your risk compared to the control group- so an HR 0f .36 for vaccinated individuals means that a vaccinated person has 1/3 the risk of an individual without vaccination or prior infection; an HR of .24 for hybrid immunity means 1/4 the risk of an individual without vaccination or prior infection; an HR of .96 for prior infection means a 4% reduction in risk when compared to individuals without vaccination or prior infection.
My takeaway: Viral load matters! If you have antibodies, you have a head start against the virus establishing a foothold in your cells. However, the antibody-virion interaction is all just a probability distribution of particles randomly bumping into each other. If you have a ton of antibodies (recently boosted or infected) the balance leans way over on the side of your immune system; as your antibodies wane, that balance starts moving more towards the virus. This study shows that the opposite is true, too: if you are exposed to a ton of virus, it can overwhelm your antibodies even though they would have protected you from a smaller viral load.
-if I’m infected, and I have already exposed my housemates before I knew I was infected, I can still greatly reduce their chance of infection by masking and isolating
-less than perfect masks, such as cloth masks or surgical masks worn poorly, might not protect you from infection in and of themselves, but they could reduce the viral load enough to help tip the balance in favor of your immune system so that mask+antibodies protects you from infection where simply antibodies would not have been enough
We already know from many studies that viral load is important in predicting severe disease, and the underlying science was pointing to this idea, but it’s always cool to get that basic science validated in a real-world setting
From a GCBR point of view, we can think of the old swiss cheese model of defense: we want overlapping layers, where the holes of one layer do not line up with the holes of another layer. In the beginning of a pandemic, we don’t have any immunity from vaccines or infections, so we need our PPE to be as perfect as possible. As we acquire immunity, we can get the same protection from less stringent PPE, even if the virus stays exactly the same.