Question in vaccines

[danmark]

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Hey guys,
here's a q that's been given to us by one of the docs on the ward, and i've got no idea how to answer it:
A mid-aged man was vaccinated when the first commercial measles vaccine came out in the USA, back in 1957.
He's a healthcare worker, and while traveling he was in Ethiopia and took care of kids with measles, without getting infected.
However, a few years later, while on the peds ward, he was again exposed to kids with measles,, and this time DID get infected and had an active measles disease.
He does not have an immune deficiency and he did not go any bone marrow transplant or other immune modifying diseases or therapies.

How can you explain that he did not get infected during the first time but did get the disease during the second time?

Thanks for your help!

 

[normtheniner]

Hey guys,
here's a q that's been given to us by one of the docs on the ward, and i've got no idea how to answer it:
A mid-aged man was vaccinated when the first commercial measles vaccine came out in the USA, back in 1957.
He's a healthcare worker, and while traveling he was in Ethiopia and took care of kids with measles, without getting infected.
However, a few years later, while on the peds ward, he was again exposed to kids with measles,, and this time DID get infected and had an active measles disease.
He does not have an immune deficiency and he did not go any bone marrow transplant or other immune modifying diseases or therapies.

How can you explain that he did not get infected during the first time but did get the disease during the second time?

Thanks for your help!

Maybe he didn't seroconvert after the first administration? And was never infected in Ethiopia?

Also, maybe the Ag targeted in the 1957 vaccine was somehow mutated in the strain that ultimately infected him? That would leave him without immunity to the virus...

I'm just throwing guesses out there.

 

[SpecterGT260]

57 was a long time ago.... many vaccines' efficacy is linked to the immune system seeing the antigen from time to time. memory cells don't last forever. Otherwise the answer above sounds good. I am not sure what the mutation rate of measles is or what the original Ag was that produced the vaccine.

 

[Go Ducks]

57 was a long time ago.... many vaccines' efficacy is linked to the immune system seeing the antigen from time to time. memory cells don't last forever.

This is almost certainly the correct answer. After getting vaccinated, he was exposed to measles from time to time in Ethiopia which kept his immunity going. Then he probably stopped going for a number of years, or maybe the area of Ethiopia he was in got measles under control, and he eventually lost his immunity. This is why you need boosters.

You can see the EXACT SAME THING happening in pockets of America, where there have been outbreaks of previously eliminated diseases among people in their 20's and 30's, whose vaccines have worn off.

 

[ijn]

The vaccine given in 1957 is not the same as the vaccine given in 2012. Adults immunized in the United States between 1957 and 1968 may not be fully protected from measles because the earlier vaccines were less effective.

 

[SpecterGT260]

The vaccine given in 1957 is not the same as the vaccine given in 2012. Adults immunized in the United States between 1957 and 1968 may not be fully protected from measles because the earlier vaccines were less effective.

efficacy alone doesn't explain the scenario. The guy worked in a measles clinic after receiving the less effective vaccine. Waning efficacy makes more sense to me.

 

[ijn]

efficacy alone doesn't explain the scenario. The guy worked in a measles clinic after receiving the less effective vaccine. Waning efficacy makes more sense to me.

Before 1968 they were giving a killed measles vaccine. It's waning efficacy in that sense. Most people get life long immunity from two shots of the live attenuated virus. You're not as likely to get life long immunity from a killed virus vaccine. It's likely he had sufficient immunity while in Ethiopia thanks to his childhood vaccination with the pre-1968 vaccine. Although I don't know how long it takes for the killed measles vaccine to lose its efficacy.

 

[SpecterGT260]

That's fine. I was just making it clear that we were talking about waning immunity and not just low efficacy. We have some vaccines which only cover a proportion of the population after administration. Such people could contract the illness regardless of time frame

Sent from my DROID RAZR using SDN Mobile

 

[ijn]

gotcha... yeah, i'm probably mangling the proper immunology terms lol

 

[Law2Doc]

... Most people get life long immunity from two shots of the live attenuated virus. You're not as likely to get life long immunity from a killed virus vaccine. It's likely he had sufficient immunity while in Ethiopia thanks to his childhood vaccination with the pre-1968 vaccine. Although I don't know how long it takes for the killed measles vaccine to lose its efficacy.

Actually many don't even have lifelong immunity from the attenuated virus. It's why you probably needed a booster shot again before starting med school/healthcare work.