Depends entirely on the particular virus or bacterium. Some are handled well by the immune system, some are not.

I think the real difference here is the availability/relevance of antibiotics vs. antivirals for treating certain symptoms. There are some situations where you can use antiviral drugs, but in many cases it isn't considered worth it (or there simply isn't an effective drug available). But we're also coming around to the fact that antibiotics probably should not be prescribed as often/freely as they have been historically.

It just depends. When you get a cut on your skin, that area is almost certainly going to get bacteria trying to grow in it. Your body will, mostly successfully, fight it off.

But... Sometimes it gets red and infected and then your body will really work at it... And then fight it off. Other times you lose a finger if left untreated.

Same with viruses. Mostly you can fight them off, but eventually one can put you in the hospital.

Then there are the scary members of both viral and bacterial families. Ebola and rabies viruses are always going to do serious damage. Likewise, there are a decent number of flesh eating bacteria that, once they take hold, are very difficult to stop.

Just to throw some other pathogens in there, if a fungal infection manages to get into your spinal fluid or lungs, that can be impossible for your immune system to fight off. Similarly, if an amoeba gets up into your brain you are hosed.

But, for every deadly virus bacteria fungus and amoeba, there are countless numbers of harmless ones that your immune system just deals with without breaking a sweat

I think it’s all down to specifics, as there can even be great variation of response to the same disease. Take covid as an example, some people had serious illness and others nothing.

About the medication, I think it’s largely about replication of said pathogen. Antibiotics are quite common as they can specifically target the bacteria, where as although antivirals exist it’s harder to target viruses which are often incorporated into host cells.

Not sure how correct my answer is so I would love any corrections if people spot something wrong

This is WAY too complicated to answer in a binary way.

EVERY immune insult is subject to hundreds/thousands of variations. We see this in action by observing the huge differences in reaction to every virus/bacterium.

It’s pretty clear from the literature that there is a period -typically- 4-10 days after viral infection where you are more vulnerable to bacterial pneumonia. This is because the immune response to combat a virus thru the production of molecules called interferons suppress some of the immune cells you need to combat bacteria. The window of vulnerability coincides with this anti-viral interferon response. In fact it’s thought that most people who died in the 1918 flu pandemic died of secondary bacterial pneumonia and not the flu per se.

Here are some references:

https://www.nature.com/articles/nm1765

https://www.jci.org/articles/view/35412

https://pubmed.ncbi.nlm.nih.gov/21178015/

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For strep throat, one of the ways the bacteria hides from the immune system is by covering itself in fragments of red blood cells. In this way it is not recognized as foreign and can keep growing. Thus the need for antibiotics. Flu in contrast has a different growth strategy. I does not plan on getting around the immune system. It makes itself so infectious that it lives in the population spreading from one to the next easily. So it is defeated in one person, but it has already spread to three others, so it fulfilled its goal of spreading its genetic material.

Here is a general answer. All bacteria and all viruses are not the same. Some bacteria for example have developed ways around the immune response. Different organisms do it differently. When you really get into the details of how each works, it is pretty fascinating. Some general examples. You have macrophages that will swallow and destroy bacteria. Some microbes figure out a way to be swallowed up, but not destroyed, and live and grow in the macrophage. Other bacteria have devised ways so they cannot be swallowed at all. And this is just scratching the surface. Some viruses actually have proteins that are immune decoys. So when they infect a cell, the virus puts a protein on the surface that says "no virus in here" so the immune system then cannot recognize that it is a virally infected cell. Other viruses, like HIV mutate so fast that by time the immune system responds to one strain of the virus, another is already growing, immune system attacks the new one, but there is yet another new one growing and on it goes. For these things that our immune system cannot fight off we need antibiotics or antivirals to help. Otherwise the patients health can be severely damaged if not actually die from the infection.

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On paper fighting bacteria is much simpler with fewer processes, but it's highly dependent on the individual.. the organism.. the state of the area infected.. so on and so forth. Simpler doesn't always mean more effective, yah know? Both can run away on you, and both have their heavy hitters like acid fast stuff/hepatitisy stuff. Treating bacterial infections is also simpler. The big difficulties most of the time being the pathogen is immune to errything you got.