Usually even in the breakthrough cases, immunity is a gradient. So while some 10% might catch Covid-19, almost all of them will have fewer and less severe symptoms than if they didn't get the shot. I would bet the cases where individuals have died after COVID are largely people that already have weaker immune systems for whatever reason (be it age or illness).

cc_ag92 said:

---

My son and I have both gotten the flu after getting the flu vaccine before. Each time, our illness was mild and shorter than other times we had gotten the flu. I discussed it with his pediatrician and she said that the flu vaccine is developed for predicted variants. When other variants appear, the flu vaccine isn't 100% effective at preventing illness, but it typically decreases the effects of the illness. I might not have this exactly right because it has been almost fifteen years since that conversation.

Based on that information, I think that's part of what is happening with breakthrough cases.

The other part is that vaccines aren't designed to be 100% effective. The effectiveness of vaccines increases when most of the community is vaccinated. My understanding is that this is true of all illnesses

---

Flu vaccine is a special case. They are guessing at strains (variants are much more closely related). It is closer to having a annual coronavirus vaccine that picks from SARS, MERS, the 4 HuCoV that cause colds, and this year COVID comes along.

If the flu vaccine includes H1N5 and you are infected with H1N1, you probably get some protection from cross reactivity of the H1s.

We are also learning that various vaccines cause some kinda of broad boost to the innate immune system. It would be interesting to see if a flu vaccine causes a similar broad immune boost that provides at least some enhanced protection against non targeted flu strains.

It is likely mutifactorial. The immune system if amazingly complicated and varies from person to person and year to year in a given person. Some people's immune system just may not kick up enough of a response to the vaccine for reasons we cannot measure.

There is also the possibility of the vaccine being handled improperly. The mRNA vaccines in particular are pretty fragile so if they stay warm a bit too long and you inject it they don't work properly. Vaccine storage and logging is actually a big deal, even for the traditional vaccines we have constant temperature logs and alarms so if the freeze goes out of range even for a few minutes we have to discard the vaccines.

Correct. You are unlikely to get it and virtually guaranteed to not die or end up in the hospital with it.

I don't understand why it's a surprise to anyone that you have to get a virus before your immune system can fight it off. Vaccines don't cause an exterior aura or forcefield to keep the virus out. Identifying positive cases just isn't enough information to be useful. They even found some in the clinical studies in sample sizes that are orders of magnitude less then current vaccination numbers.

cc_ag92 said:

---

Thanks for the clarification.

So, what does that mean for the efficacy of other (Covid or non-Covid) vaccines? Are any of them 100% effective? This is definitely not my area of expertise, but it was never my understanding that any vaccines are effective 100% of the time.

What is your understanding of breakthrough cases?

---

Nothing is 100%. Although efficacy isn't what a lot of people think it is. Efficacy is calculate by comparing the number of control (placebo) subjects who get sick to the number of test (vaccinated). In the case of COVID, they were looking at severe cases, hospitalization and death. So an efficacy of 99% doesn't mean 1% will get a bad case. Rather it is a 99% reduction in the number of people who would have been hospitalized or died. We don't really know the efficacy at preventing infection.

Now, why breakthroughs? You inject something to expose the body to the spike protein. The immune system makes antibodies to bind to the surface. However, there is a lot of surface relative to the binding site on an antibody, so your immune system ends up making a bunch of different antibodies and then tries to select for the best ones. Antibodies are also classified into 2 groups, those that bind and can signal the immune system to attack and those that also block the spike protein from doing its thing. This might block the binding of the spike protein to the receptor or it might lock the spike protein into one conformation. When the spike protein binds the receptor, there is a shape change to inject the viral RNA into the cell. Can't bind and/or change shape, can't infect a new cell. About 20% of the people in the early trials developed the interfering antibodies. The other 80% only had antibodies that triggered an immune response, but didn't block infection.

I think looking at a positive test result without a clinical presentation is not very helpful, so I'll limit breakthrough infections to people who actually get sick. since we already know that people have different sets of antibodies and some antibodies are better than others, I suspect part of the breakthrough infections are people with less effective antibodies. They can still work, keep the infection/symptoms in check, but didn't completely eliminate the virus at an early stage. There are other reasons as well, including some people have weaker overall immune systems for a variety of reasons.

Another possibility is that things just didn't work and the person didn't develop effective antibodies for some reason. That doesn't lead to a milder case than unvaccinated, but difficult to tell if a mild case is less severe than it would have been or the same since many people only had mild cases anyway.