What happens if you get vaccinated but have the disease?

Hello Everyone,

I’m betting the answer is nothing, but what happens if you get vaccinated for let’s say the measles or hpv or whatever, but you are already infected with the disease? Obviously the vaccine wouldn’t cure the disease, but could it make it worse?

It depends on the vaccine somewhat. For most of them, depending on where you are in the contagion cycle, either you might have fewer symptoms, you might have worse symptoms, or nothing difference at all.

Some vaccines are designed for exactly this case: the rabies vaccine in humans, for example, is typically given after exposure.

But for many people the important answer, I think is this one: they’ll believe that the vaccine gave them the illness (even–perhaps especially-when symptoms appear too soon after inoculation for the disease to have been contracted at vaccination time). For something like measles or polio, this is going to be so rare in modern industrialized countries that it doesn’t matter. But for something common like the flu, which affects millions of people a year and is often confused with even more common illnesses, that will result in a large enough number of people for whom this happens that their anecdotal data will cause even normally rational people to conclude false things like: the flu vaccine can give you the flu. And the Internet will spread that belief like its own virus.

I had this conversation this morning with the NP who gave me a flu shot. I was feeling a bit off yesterday. My throat slightly sore. I told her. She said not to worry about it.
But, nurse-y I do worry. Coz?, well…I am a fretter. She just gave me the ‘it’ll be okay smile and pat on the shoulder’. I got the shots anyway. I’ll let you know if it kills me.

I don’t really know or understand how the bodies goes about creating anti-bodies and fighting off diseases. Is there are chance that if you get a vaccine while you are sick with that illness that your body will waste its disease-fighting resources fighting off the dead/inactive viruses or bacteria that were injected into you instead of using them on the real viruses or bacteria, thus prolonging the sickness?

No, if anything it will potentiate the attack on the “real viruses or bacteria” by additionally stimulating the immune system.

I don’t know of contraindications to getting any vaccine if it’s thought that the recipient might already have the disease - except of course that it would be unnecessary, represent wasted money spent and pose the usual (small) risks associated with vaccination like an allergic reaction.

It may be beneficial for those already positive for HPV to get the HPV vaccine (Gardasil). The vaccine protects against multiple viral strains and it’s highly unlikely that the existing infection involves all of them. So in the common scenario of the existing infection clearing on its own*, the vaccinated individual would be protected against re-infection by all the high-risk viral strains included in the vaccine.

*this is thought to happen in over 90% of cases. The problem is that we’re unable to tell which infections will spontaneously clear and which will dangerously persist.

It would depend on the vaccine, and where the person was in the whole infectious-disease process.

Gamma globulin, the precursor to vaccines, is still occasionally given post-exposure for some diseases. It doesn’t always prevent them, but it can reduce the severity and does offer some temporary partial immunity.

The shingles vaccine was given to Mr.Wrekker at his last check-up. I reminded him he had the Shingles a few years earlier, when he got home. It didn’t seem to affect him in any way.

Maybe it’s beyond the scope of the OP, but Immune-Complex Disease could be worsened via vaccination. Basically, the antigen-antibody complex itself can cause problem like vasculitis or glomerulonephritis.


I don’t see anything in that excerpt about vaccines (and of course lupus is not something one is ‘‘infected’’ with; the OP was asking about vaccination if one is already infected).

Vaccination is a valuable tool in the treatment of lupus patients (who are commonly at increased risk of some infectious diseases, like invasive pneumococcal disease).

*"Take-Home Messages
Patients with SLE are at an increased risk of infection, especially if they are taking immunosuppressive medication.

Although the history of vaccination in SLE patients had been controversial, the risk benefit balance is in favor for vaccination to reduce the risk of infection as compared to the risk of flare.

Inactivated vaccines are safe to administer to SLE patients on immunosuppression whereas live vaccines are contraindicated in patients on immunosuppressive medication.

If possible, vaccination should be administered before starting immunosuppressive medication, as once it is started then live vaccines are contraindicated and responses to non-live vaccines may be suboptimal."*

Related questions.

What vaccines shouldn’t you get if you’re on immunosuppressants/immunocompromised?

What vaccines should you get if you’re on immunosuppressants/immunocompromised?

(I’m on Mycophenolate for my Myasthenia.)

CMC fnord!

I almost posted a very similar question as the OP about a month ago after reading that there’s some fairly compelling evidence that alzheimer’s might be caused by the virus that causes gingivitis going to the brain and that a gingivitis vaccine is in development.

“Fairly compelling” seems to be a bit of an overstatement, although the results were interesting. Correlation isn’t causality.

It’s a good idea to brush your teeth, of course.


I’ve mentioned this in the past:

Since my teens (and probably earlier) I had chronic Hepatitis B.

The Hepatitis B virus expresses two antigens - a surface antigen, and a core antigen. Most people develop an immunological response to both the surface and the core antigen, and get over Hepatitis B.

About 10% of the population, and a much higher proportion of newborn infants, only develop an immunological response to the surface antigen - they never clear the disease, but also don’t really get sick. Without antibodies to the core antigen, the virus just makes the sufferers liver a battleground, and eventually cirrhosis develops (and possibly hepatic cancer). Lifestyle factors (drinking, exposure to some food toxins such as nut-borne aflatoxins) make this outcome much more likely.

Modern antivirals (similar to and in some cases the same as HIV antivirals) can be used to control the Hep-B virus, and I was on antivirals for several years with basically zero viral load. But I was on the antivirals for life. This wasn’t a problem, as the antivirals are generally well tolerated, and I lived in places with a public health system that meant there was no cost to me for the drugs.

A few years back I took part in a trial - a vaccine-based approach that used a genetically modified yeast extract that expressed the Hep-B core antigen. The hope was that this would prompt the immune system into expressing core antibodies so the virus would clear. That trial had no major effect, but obviously did have an impact on the immune system, because they persisted with a new trial.

A year later, I was invited to join this new trial, where the same antigen extract was used combined with an immune system modulator (a PCD-1 modulator used for some cancer treatments) to extend the period of immune system activity. PCD-1 modulators (where PCD means Programmed Cell Death) prevent the automatic death of immune system cells, extending their period of activity and the number of active immune cells in the system.

I was given the trial drugs, and after two weeks was called by the co-ordinator to say my liver function markers were very high, and they were concerned that I might be having an autoimmune response to the PCD-1 modulator. I had to cancel a trip to the US at short notice, and had lots more monitoring until my liver function results were back to normal.

What was actually happening was the combination of the vaccine and the PCD-1 modulator had temporarily supercharged my immune system, and I had developed those Hep-B core antibodies I had been missing for 30+ years. Six months later I stopped taking antivirals, and stopped monitoring a few months after that.

Sadly, I was the only patient in the trial to respond in that way, but research is continuing.

So vaccine-based approaches can be used to actually treat the disease - particularly if the vaccine can be used to activate the immune system while a disease is in a low activity or latent phase (as with rabies).