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There seems to be recurrent events of infections of the plage (Yersinia pestis), from the well known Justinian plague to the Black Death and to recent years. In fact, two cases were reported in China in November 2019. However, it seems there is not an effective vaccine yet. At least until 2013 there was no vaccine approved by the US FDA. There seems to be on-going research about vaccines for the plage.

Is then no effective vaccine against the plague? If yes, does it mean humanity is still at risk of yet another pandemic of the plague?

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There is little motivation right now for vaccination against plague because:

  1. Human infections with plague are fairly rare. A vaccine administered to the general populace would have to be very cheap and extremely safe to make it cost-effective and have a net benefit given the risks of plague are so low, and because

  2. Antibiotics are effective against plague - this makes the likelihood of a widespread outbreak fairly low. Antibiotic resistance could be a concern, but plague would not be one of the most concerning pathogens from that perspective - there isn't much exposure to antibiotics in the reservoir species that the bacterium lives in, so there is less selective pressure towards resistance compared to other bacterial pathogens.

Additionally, plague lives in reservoir species, so extensive human vaccination is not a plausible way to eradicate the bacteria entirely, unlike pathogens that have humans as a primary host.

That said, vaccines are available and can be used for certain individuals at high risk. However, they take a long time to show immune protection (>1 month) making them not that useful during outbreaks. From the same WHO report linked above:

Worldwide, live attenuated and formalin-killed Y. pestis vaccines are variously available for human use. The vaccines are variably immunogenic and moderately to highly reactogenic. They do not protect against primary pneumonic plague. In general, vaccinating communities against epizootic and enzootic exposures is not feasible; further, vaccination is of little use during human plague outbreaks, since a month or more is required to develop a protective immune response. The vaccine is indicated for persons whose work routinely brings them into close contact with Y. pestis, such as laboratory technicians in plague reference and research laboratories and persons studying infected rodent colonies (23).

WHO plague manual:

https://www.who.int/csr/resources/publications/plague/WHO_CDS_CSR_EDC_99_2_EN/en/

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    $\begingroup$ So basically, a cheap, widespread and effective antibiotic based treatment exist? I guess that is the benefit of the plague being a bacterial and not a viral disease like Covid-19. $\endgroup$
    – luchonacho
    Apr 29, 2020 at 18:31
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    $\begingroup$ @luchonacho Yes, exactly. Plague is still dangerous because the antibiotics need to be given quickly, but antibiotic resistance is relatively rare for plague. $\endgroup$
    – Bryan Krause ♦
    Apr 29, 2020 at 18:32
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    $\begingroup$ It might be worth pointing out that the main reason why antibiotic resistance is of limited concern with Y. pestis is that the natural reservoir from which it sometimes jumps to humans consists of wild rodents, which (unlike humans and domesticated livestock) aren't normally treated with antibiotics. Thus, there's little to no selection pressure for Y. pestis to evolve antibiotic resistance in its natural hosts. $\endgroup$
    – Ilmari Karonen
    May 2, 2020 at 13:53
  • $\begingroup$ @IlmariKaronen Indeed, I thought I implied that but I guess I never did! I'll edit. $\endgroup$
    – Bryan Krause ♦
    May 2, 2020 at 14:58
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There is already plague vaccine in use, which is only administered to lab workers working on Y. Pestis or people residing in areas affected with plague. (Via: https://www.cdc.gov/mmwr/preview/mmwrhtml/00041848.htm)

Plague can also be treated with antibiotics if detected at earlier stage (such as streptomycin, ciprofloxacin, gentamicin or doxycycline). Very few antibiotic resistant strains of Yersinia pestis have been reported till now. So, this may not become the reason for pandemic.

As it is known, Y. pestis exhibits intrinsic genetic plasticity to transform into antibiotic resistant strain, which makes it potent agent of bioweapon. So, Centers for Disease Control has listed Y. pestis under the category A select agent. And researchers are working for development of next generation vaccine which is more reliable by exhibiting strong cellular immune response. (Via: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5155008/)

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