Vaccines and immunity.

 Vaccines don't make you "immune" to a virus. Nor are they 100% effective or instantly effective.

These are important things to keep in mind in the face of reports that a nurse contracted COVID-19 a week after receiving the vaccine.

In short, there are a plethora of reasons why this nurse may have contracted the virus which are perfectly benign.

First thing up is the timeline; a week after the injection. That would be when symptoms presented, and possibly also after the test and waiting on results. In short, the claims that it was contracted the night prior to the symptoms while working in the COVID unit stand a high chance of being factually incorrect.

COVID symptoms RARELY present that quickly. He may have been infected already at the time of the shot. Or, more likely, shortly thereafter.

The assumption that it came after a night in the COVID unit seems more likely to be the brain jumping to what feels like the most rational answer. Even though it isn't actually rational at all. Now, I don't know the full details of this individual's work schedule. But, it seems likely if they worked in the COVID unit on one occasion that they did on others as well. Furthermore, hospitals are a gathering place for the infected in general. And it is also quite possible that this individual started relaxing following guidelines after getting the shot.

Even if none of that is true, it is still statistically far more likely it was contracted on another day and via another path. Basically, the incubation period is a function of how long it takes the viral load in the person to reach a tipping point of sorts. Many people work in those COVID units and I'll wager the procedures in place reduce both the odds of infection and the initial viral load they would have contracted. So, unlikely.

Again though. Let's assume this hunch is correct. The next two barriers relate to effectiveness. Firstly, it is reported to take 10-14 days for the vaccine to reach it's full potential and the first shot only have a reported 50% effectiveness. It doesn't reach that nice 95% number until the second dose has "settled in". So, even if it was that one fateful night, with just a single dose and not past 10-14 days this individual would have had less than a 50% chance of avoiding serious infection.

The final problem is fixating on this. Even if this nurse had taken both shots already and had done so, say, more than a month ago it may not have stopped a case like this. COVID-19 is still rampant in the community and the odds of any one person coming into contact with it are still quite high. And this vaccine is not 100% effective.

And, there is no such thing as "immunity". Immunity really only comes if we successfully eradicate the virus. The immunity a vaccine grants you is simply the ability for your immune system to detect and effectively eliminate an infection. Therefore, if the immune system is to do its job, you must actually get infected first. I wouldn't call that immunity in the classical sense of the word.

This is why some officials fear that vaccination may not actually eliminate the virus. It is quite possible that the virus can still infect a vaccinate person sufficiently for them to be contagious for a time, even if it prevents the worst of the symptoms. 

However, I'm not advocating for avoiding the vaccine. This is simply to set the record straight on why this isn't the last time we will hear such stories. The effectiveness of vaccination will be shown through the decrease in overall cases as the percentage of vaccinated people in the population grows. And then continue to remain low or lessen even as restrictions ease after that. 

 In the meantime you'll hear all manner of stories of vaccinated people catching or spreading the virus. Though, the incidence rate should be substantially lower than in the un-vaccinated public.