There actually used to be a shot for Typhoid but it made you sick as a dog for several days. The oral vaccine came later, with fewer side effects. Sorry I don;t know the details, just wanted to point out typhoid vax has not always been in pill form. I think the pill form is more desireable for most people (who doesn’t hate shots?)
The oral typoid vaccine is made from a live virus. The oral polio vaccine was also a live version as is the flu vaccine when it’s given in a nasal mist form.
Vaccines that use live viruses produce better immunity than those which use dead viruses. Of course the virus is weakened, but in small number of cases the vaccines which use live viruses can actually cause the diease instead of just giving you immunity.
This is why the oral polio vaccine was discontinued.
If you look at the CDC site you will see fever, redness, headache and swelling occur in about 5-7% of the typhoid shot type vaccine
If you look at the oral vaccine the side effects are listed as fever 3% - 5% and very rare abdominal discomfort.
So it does seem the oral vaccine in additon to being more convenient, has fewer side effects.
Obviously anyone with HIV or any other immune problems should not get a vaccine with a live virus, whether it’s typhoid or the nasal mist flu type vaccine.
Your gut is contains patches of lymphoid tissue, which are a part of your immune system. Both typhoid and polio infect the intestinal tract (polio then goes on to spread from the intestinal tract to the central nervous system, where it causes paralysis). The lymphoid tissues of the intestinal tract react to the infection by producing antibodies (IgA); this happens BEFORE the rest of the immune system elsewhere in the body kicks into antibody production (IgG antibodies).
A killed-organism vaccine, which is given by injection, triggers the general-body IgG immune response, but not the IgA gut immunity. An oral vaccine is made from a live but weakened strain of the virus or bacterium, and causes a low-level (and hopefully non-symptomatic) infection, just as the naturally-occurring disease organism does, and thus triggers both the gut-mediated IgA early immune response and the later generalized whole-body IgG immune response. This results in a much stronger immune response later, when the body encounters the real thing; the gut immunity can kick in almost immediately, and stops the nascent infection in its tracks before it can even begin to take hold. The risk, though is that a weakened live-organism vaccine does have a small chance of actually causing a significant infection (which is the very thing immunization is supposed to avoid). So oral live-organism vaccines aren’t generally given to people who have known immune system problems, and when a disease becomes very rare in a population (as polio is in the US now), it makes sense to switch over to the killed-organism vaccine once the risk of developing the disease due to the vaccine itself becomes higher than the risk of contracting it “in the wild”.