# Why do we develop immunity to viruses but not bacteria? **URL:** \ **Category:** Factual Questions\ **Created:** [October 4, 2025, 2:38pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672 "2025-10-04T14:38:16Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [October 4, 2025, 2:38pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/1 "2025-10-04T14:38:16Z")
I asked a few questions in [another thread from 2003](https://boards.straightdope.com/t/whats-the-difference-between-bacteria-and-a-virus/150038/4), and parts of my questions were answered but not the one in my subject line here. There are some vaccines against bacterial infections, like TB, but not for things like strep. I’ve had strep a dozen times, but you get chicken pox once and you’re done. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [October 4, 2025, 4:03pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/2 "2025-10-04T16:03:59Z")
> [@CookingWithGas](#): > > There are some vaccines against bacterial infections, like TB The TB vaccine is not really used much and may be minimally-effective. The more common bacterial vaccine is for tetanus. Viruses are not really living things. They consist of a protein shell containing the data (usually in RNA form) needed to make more of that type of virus. They have no progressive metabolic processes, just an injection mechanism to force the host to produce more viruses. They have no real life cycle outside of parasitic replication. Defeating them is a matter of disabling their ability to replicate, which could, theoretically, be as simple as clogging their injection point. Bacteria, by contrast, are unmistakably living things, which have their own metabolic processes and usually reproduce on their own. It is typically the reproductive process where stuff like antibiotics cause bacteria to fail, because a large fraction of bacteria do not attack the living host but create other issues (like toxic by-product generation). In fact, the human microbiome includes a staggering contingent of symbiotic bacteria without which we would be dead. Bacteria have a lot of cell wall proteins, and most of them are commonplace, so identifying one surface protein to mark can be a major challenge. It might not even be possible in some cases to distinguish a harmful bacterium from a harmless or important type. It is a far greater challenge to defeat dangerous bacteria _a priori_ than with much simpler viruses. ---
**Author:** ![Marvin\_the\_Martian](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/marvin_the_martian/32/2898_2.png) [@Marvin\_the\_Martian](https://boards.straightdope.com/u/Marvin_the_Martian)\ **Post date:** [October 4, 2025, 4:21pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/3 "2025-10-04T16:21:43Z")
Here is an article explaining some of the difficulties in developing vaccines for bacteria: > **[Why Don’t We Have a Vaccine For…A Tale of 3 Pathogens | ASM.org](https://asm.org/articles/2022/july/why-don-t-we-have-a-vaccine-for-3-pathogens)** > > Despite years of effort, we still don’t have vaccines against Pseudomonas aeruginosa, Staphylococcus aureus and Neisseria gonorrhoeae. Why not? And how can researchers move past the hurdles? ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [October 5, 2025, 11:58am UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/4 "2025-10-05T11:58:31Z")
> [@CookingWithGas](#): > > but you get chicken pox once and you’re done. Until you get shingles ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [October 5, 2025, 6:39pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/5 "2025-10-05T18:39:27Z")
> [@CookingWithGas](#): > > I’ve had strep a dozen times, but you get chicken pox once and you’re done. We discussed this a while back - chicken pox is one of those things that you can get more than once (not even counting shingles): > [@No, we don't all need to "get it eventually"](https://boards.straightdope.com/t/no-we-dont-all-need-to-get-it-eventually/851344/62): > > I found this paper from the Journal of the American Association of Pediatrics [https://pediatrics.aappublications.org/content/109/6/1068?sso=1&sso\_redirect\_count=1&nfstatus=401&nftoken=00000000-0000-0000-0000-000000000000&nfstatusdescription=ERROR%3A+No+local+token](https://pediatrics.aappublications.org/content/109/6/1068?sso=1&sso_redirect_count=1&nfstatus=401&nftoken=00000000-0000-0000-0000-000000000000&nfstatusdescription=ERROR%3a+No+local+token) "Results. Among varicella cases reported to the surveillance project, 4.5% of cases in 1995 and 13.3% of cases in 1999 reported previous varicella. More than 95% of first infections were physician diagnosed, epidemiologically linked… ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [October 6, 2025, 3:22pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/6 "2025-10-06T15:22:24Z")
Sometimes they’re challenging to develop for various reasons, but the numerous vaccines against bacterial pathogens include ones for meningococcal disease, (Strep) pneumococcal pneumonia, Haemophilus influenzae, tetanus, diphtheria and pertussis. Article [explaining](https://asm.org/articles/2022/july/why-don-t-we-have-a-vaccine-for-3-pathogens) why it’s been tough developing vaccines against targets like Staph aureus and Pseudomonas. Antigenic diversity, complexity of effective immune responses and lack of good animal models for vaccine studies are cited. ---
**Author:** ![EnolaStraight](https://avatars.discourse-cdn.com/v4/letter/e/41988e/32.png) [@EnolaStraight](https://boards.straightdope.com/u/EnolaStraight)\ **Post date:** [October 10, 2025, 3:48pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/7 "2025-10-10T15:48:35Z")
I believe the germ’s genetic code has something to do with it. Viruses that run on DNA have surface antigens which are fixed, and thus the body’s immune system can create antibodies to neutralize the germ. RNA based viruses (and bacteria?) create variable surface antigens which change faster than an immune system to keep up. ---
**Author:** ![Melbourne](https://avatars.discourse-cdn.com/v4/letter/m/b5e925/32.png) [@Melbourne](https://boards.straightdope.com/u/Melbourne)\ **Post date:** [October 22, 2025, 4:49am UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/8 "2025-10-22T04:49:35Z")
> [@eschereal](#): > > The TB vaccine is not really used much and may be minimally-effective. The more common bacterial vaccine is for tetanus The TB vaccine is not really used much in the USA because (1) There is a national shortage of TB vaccine in the USA, and (2) The USA does not have a high level of TB. TB vaccine is highly effective in preventing TB in young children. “May be minimally-effective” is true, but those are weasel words. It also “May be effective”. Nobody thought about making statements about the effectiveness of BCG twenty years ago: what changed was the lack of supply in the USA, and the possibility of new mRNA vaccines. BCG is an attenuated virus vaccine. Unlike COVID mRNA vaccines, which have demonstrated safety in billions of people, BCG is not a ‘safe’ vaccine. It’s given to people who work with TB infected people (in health care, or indigent care), and it’s used in areas with high levels of endemic TB. ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [October 24, 2025, 8:46pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/9 "2025-10-24T20:46:01Z")
BCG is mostly used in the U.S. as immunotherapy for early stage bladder cancers. > **[BCG Treatment: What It Is, Procedure & Side Effects](https://my.clevelandclinic.org/health/treatments/17908-bacillus-calmette-guerin-bcg-treatment)** > > BCG treatment delivers immunotherapy drugs through a catheter directly to your bladder. It’s the main immunotherapy used to treat early-stage bladder cancer. It may also have application for treating other non-infectious disorders. ---
**Author:** ![nearwildheaven](https://avatars.discourse-cdn.com/v4/letter/n/90db22/32.png) [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)\ **Post date:** [October 24, 2025, 10:04pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/10 "2025-10-24T22:04:21Z")
Diphtheria, hemophilus influenzare and pertussis are also bacterial diseases. ---
**Author:** ![nearwildheaven](https://avatars.discourse-cdn.com/v4/letter/n/90db22/32.png) [@nearwildheaven](https://boards.straightdope.com/u/nearwildheaven)\ **Post date:** [October 24, 2025, 10:08pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/11 "2025-10-24T22:08:42Z")
That’s the only thing I ever saw it used for. I have no idea who figured out this might work, or why, but for some (usually) men, it does, with minimal side effects beyond local discomfort. Before doing clinicals in 1994, all of us pharmacy students had to have TB tests, at the school’s expense. All but two, who were friends of mine, were able to use the PPD, but they had to get chest x-rays because they had emigrated from Uganda and Hong Kong in the 1970s, and had to get a BCG vaccine to enter the country. People who have had a BCG will usually register a false-positive for a PPD. AFAIK, all the tests for the 86 of us were negative. ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [October 24, 2025, 10:32pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/12 "2025-10-24T22:32:47Z")
> [@eschereal](#): > > Viruses are not really living things. They consist of a protein shell containing the data (usually in RNA form) needed to make more of that type of virus. They have no progressive metabolic processes, just an injection mechanism to force the host to produce more viruses. They have no real life cycle outside of parasitic replication. I find this fascinating. Enough so that I did a little digging. Since the OP has mostly been answered, I hope it’s OK to post this synopsis on the origin/evolution of viruses: 'The exact origin of viruses remains a topic of scientific debate. Several hypotheses have been proposed, but none have been definitively proven. Hypothesis 1: Ancient Cells This hypothesis suggests that viruses originated from ancient cells that existed before the Last Universal Common Ancestor (LUCA). Over time, these cells may have lost their ability to replicate independently and became dependent on host cells for survival. (this has the makings of a good sci-fi story) Hypothesis 2: Escape from Host Cells This hypothesis proposes that viruses originated from genetic elements that escaped from host cells. These elements, such as plasmids or transposons, could have acquired the ability to replicate and spread between cells, eventually evolving into viruses. Hypothesis 3: RNA World Hypothesis This hypothesis suggests that viruses originated in the RNA world, a hypothetical period in early Earth’s history when RNA was the primary genetic material. RNA molecules may have self-replicated and evolved into primitive viruses that could infect early cells. Hypothesis 4: Hybrid Origin This hypothesis proposes that viruses may have originated from a combination of different sources, such as ancient cells, genetic elements, and RNA molecules.’ ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [October 24, 2025, 11:02pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/13 "2025-10-24T23:02:20Z")
> [@Lucas\_Jackson](#): > > I find this fascinating. Enough so that I did a little digging. Since the OP has mostly been answered, I hope it’s OK to post this synopsis on the origin/evolution of viruses: > > 'The exact origin of viruses remains a topic of scientific debate. Several hypotheses have been proposed, but none have been definitively proven. Here’s a bit more information about the competing hypotheses of viral origins: > **[Where Do Viruses Come From?](https://biodiversity.utexas.edu/news/features/where-do-viruses-come)** > > This article explores the origin of viruses We tend to lump different families of viruses into one big overarching group but the realms of viruses are so different that if they were considered independent domains of life. There may not be a singular modal origin for all visuses but it is clear that at least some families are, in fact, free floating RNA or derivatives of organelles which escaped from cells and became capable of replication by infecting host cells. We tend to think of viruses as pathogens but there are plenty of viruses that do no harm and may even sometimes provide benefit to their hosts. No area of biology—even neuroscience—is as complicated an has so many “unknown unknowns” as virology and viral immunology. Stranger ---
**Author:** ![Lucas\_Jackson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lucas_jackson/32/303_2.png) [@Lucas\_Jackson](https://boards.straightdope.com/u/Lucas_Jackson)\ **Post date:** [October 25, 2025, 11:05am UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/14 "2025-10-25T11:05:28Z")
Thank you, Stranger, for that link. ---
**Author:** ![Darren\_Garrison](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/darren_garrison/32/92_2.png) [@Darren\_Garrison](https://boards.straightdope.com/u/Darren_Garrison)\ **Post date:** [October 25, 2025, 12:08pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/15 "2025-10-25T12:08:29Z")
> [@Lucas\_Jackson](#): > > 'The exact origin of viruses remains a topic of scientific debate. Also, there are several different groups of viruses, with the groups being basically more different from each other than elephants and rutabagas. There is likely more than one completely different origin. > **[Baltimore classification](https://en.wikipedia.org/wiki/Baltimore_classification)** > > Baltimore classification is a system used to classify viruses by their routes of transferring genetic information from the genome to messenger RNA (mRNA). Seven Baltimore groups, or classes, exist and are numbered in Roman numerals from I to VII. Groups are defined by whether the viral genome is made of deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), whether the genome is single- or double-stranded, whether a single-stranded RNA genome is positive-sense (+) or negative-sense (–), and wh... (Try to wrap your head around this) > Excluding ribozyvirians, RNA viruses of groups III–V are believed to share common ancestry.[[2]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-koonin2020-2)[[3]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-koonin2021-3) +ssRNA viruses form the basal, ancestral lineage of these viruses from which dsRNA viruses and –ssRNA viruses appear to have evolved from on multiple occasions.[[3]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-koonin2021-3)[[66]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-zayed-71) The two orders of RT viruses in the class _Revtraviricetes_, _Blubervirales_ and _Ortervirales_, are believed by virologists to have evolved from two different families of [retrotransposons](https://en.wikipedia.org/wiki/Retrotransposon) on separate occasions.[[114]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-koonin2024-119) ssRNA-RT viruses all belong to _Ortervirales_ and thus share common ancestry.[[3]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-koonin2021-3)[[72]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-krupovic2018-77) dsDNA-RT viruses, on the other hand, are found in both orders and therefore represent two separate lineages of dsDNA-RT viruses.[[72]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-krupovic2018-77)[[98]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-caulimo-103) Ribozyvirians constitute a lineage of –ssRNA viruses unrelated to other RNA viruses.[[3]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-koonin2021-3) > > Most ssDNA viruses likely originate from [plasmids](https://en.wikipedia.org/wiki/Plasmid) that, on multiple occasions, [recombined](https://en.wikipedia.org/wiki/Genetic_recombination) with other genomes to obtain the structural proteins needed to form virions.[[2]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-koonin2020-2)[[3]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-koonin2021-3) The evolutionary history of dsDNA viruses is the most complex as they appear to have emerged independently on numerous occasions. Two major lineages of dsDNA viruses exist: the realm _Duplodnaviria_ and the realm _Varidnaviria_, the latter of which also contains ssDNA viruses that are descended from dsDNA viruses. The opposite is true in the realm _Monodnaviria_, which contains dsDNA viruses descended from ssDNA viruses. There are also two minor realms, _Adnaviria_ and _Singelaviria_,[[22]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-vzsingela-25) that exclusively contain dsDNA viruses. Lastly, there are dsDNA virus families unassigned to higher taxa that are unique from existing realms and which likely constitute small realms.[[2]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-koonin2020-2)[[3]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-koonin2021-3) > > Of the replication-expression systems used by viruses, only Baltimore group I (dsDNA) is typically used by cells.[[2]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-koonin2020-2) The other groups may be remnants of the primordial stage of life before the emergence of modern-like cells, during which the dsDNA system used by extant cells had not yet become uniform. The ancestors of RNA viruses in particular may have emerged during the time of the [RNA world](https://en.wikipedia.org/wiki/RNA_world). And although virus realms are evolutionarily independent from each other, the replicative proteins encoded by viruses in the four major realms (_Duplodnaviria_, _Monodnaviria_, _Riboviria_, and _Varidnaviria_) are built on the core [RNA recognition motif](https://en.wikipedia.org/wiki/RNA_recognition_motif), one of the most common nucleic acid-binding [domains](https://en.wikipedia.org/wiki/Protein_domain) in nature. Therefore, the replication-expression cycles most likely diversified before the separation of large dsDNA replicators, which became the ancestors of cellular life, from other types of replicators, which became [selfish genetic elements](https://en.wikipedia.org/wiki/Selfish_genetic_element) and gave rise to viruses.[[3]](https://en.wikipedia.org/wiki/Baltimore_classification#cite_note-koonin2021-3) ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [October 25, 2025, 3:22pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/16 "2025-10-25T15:22:14Z")
> [@Stranger\_On\_A\_Train](#): > > We tend to lump different families of viruses into one big overarching group but the realms of viruses are so different that if they were considered independent domains of life. I seem to have failed to complete expressing that thought; that should read: > … but the realms of viruses are so different that if they were considered independent domains of life _the would be un different kingdoms_. “Virus” is more of an extremely broad functional description rather that a distinct classification, and as a world-class virologist explained to me (over a game of [_Pandemic_](https://boardgamegeek.com/boardgame/30549/pandemic) a few years before COVID-10), we really have no idea how many types of viruses exist in the world because research are almost exclusively focused an viruses that are pathogenic or present a cross-species ‘spillover’ threat to humans, livestock, and agriculture, and there are vastly more individual virions than living organisms on the planet even compared with bacteria and archea. I also asked her if she thought that extraterrestrial life would have some analogue to viruses (because we share an interest in astrobiology), and she responded that if the use proteins and encode heritable data in some analogue of a genome, then they almost certainly have their own counterpart to viruses even if they aren’t specifically DNA and RNA. Stranger ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [November 9, 2025, 12:31pm UTC](https://boards.straightdope.com/t/why-do-we-develop-immunity-to-viruses-but-not-bacteria/1023672/17 "2025-11-09T12:31:18Z")
> [@Stranger\_On\_A\_Train](#): > > “Virus” is more of an extremely broad functional description rather that a distinct classification, and as a world-class virologist explained to me (over a game of [_Pandemic_](https://boardgamegeek.com/boardgame/30549/pandemic) a few years before COVID-10), we really have no idea how many types of viruses exist in the world because research are almost exclusively focused an viruses that are pathogenic or present a cross-species ‘spillover’ threat to humans, livestock, and agriculture, and there are vastly more individual virions than living organisms on the planet even compared with bacteria and archea. A very good point. We don’t study “viruses” - we study “viruses that come to our attention because they either kill us or kill our foodstuff” > [@Stranger\_On\_A\_Train](#): > > I also asked her if she thought that extraterrestrial life would have some analogue to viruses (because we share an interest in astrobiology), and she responded that if the use proteins and encode heritable data in some analogue of a genome, then they almost certainly have their own counterpart to viruses even if they aren’t specifically DNA and RNA. If I recall correctly, when computer scientists invented an “artificial life” environment where programs competed to replicate, parasitic virus-like computer programs soon evolved, even though they were not deliberately created.