The Difference between a Live and Dead Immunizations:
One Needs Boosters, the Other May Not
A lot of colleges are now requiring entering students to have 2 chickenpox vaccines, and this has led to many questions about why some vaccines require regular repeat dosages (boosters), why some don't. This essay is a bit technical, but explains why this is so.
It turns out that not all immunizations are the same sort of immunization.
One aspect that all immunizations share is that they present the body with the illusion that it is being infected with a germ, the body responds by creating its defenses, and as along as those defenses remain in place, the real germ is kept from creating a real infection. For example, the polio immunization tricks the body into thinking a real polio infection is happening. The body's response leaves the body fully defended from real polio germs, and if they come by, cannot cause polio.
So, all immunizations use this approach and strategy, but some are living, and some are not, and that can impact on how many doses you need to create and maintain the protection.
Non-Living Immunizations
Nearly all immunizations routinely used for American children are not live, but made out of non-living materials derived from a once alive germ. These include the very familiar immunizations for diphtheria, tetanus and pertussis (the DTaP for young kids and TDaP for older people), all the meningitis shots, the HPV vaccines, the polio vaccine, and hepatitis A and B.
The key property of non-living, or dead immunizations, is that the body does not totally believe that a real infection has taken place. Most of the defenses that allow us to survive and triumph over an infection take place after immunization with inert material, but not all. So after getting an immunization with non-living material, you are protected, but the protection wanes, and after some period of time, disappears. So, if after you are born you get one tetanus shot, you will have protection against tetanus for 2 months, but that's it.
The other property of non-living immunizations, is that if you repeat the dose, the time the protection lasts gets longer. Taking the tetanus example, if you get one shot every two months for a total of 3 tetanus shots, you will be protected for one year, and after a fourth dose at the end of that year long interval, you will be protected for 7 years!
So almost all non-living immunizations require an initial series of immunizations, to keep protection in place, and to lengthen how long you are protected between repeat doses. But even once you achieve protection for 10 or more years, one typically sees protection weaken. That is why all of these types of immunizations typically require boosters, or repeat dosages over long periods of time.
Three exceptions to this rule are the Hepatitis A and B, and HPV immunizations, which do not require boosters over time.
Living Immunizations
There are not many living immunizations, and they all are for diseases whose germs are viruses.
There are very, very few live immunizations containing live bacteria.
The reason for both these facts has to do with the central challenge of a live immunization. How do you put a live germ in someone and avoid causing the infection?
No one has figured out how to weaken a bacteria to the point it won't make you ill, but still keep it live enough to provide immunity.
But that has been figured out for a variety of viruses. It turns out you can grow viruses in a way that renders them very, very weak, but still capable of reproducing a few times in your body before dying off. This allows for some immunizations to deliver a very, very weak form of the germ, so weak you don't get ill, but still alive enough to really convince the body it is experiencing a real infection.
If the body thinks a very real infection has occurred, then it goes all the way in defending against it and creates mechanisms to produce protection for the rest of the person's life. This is called life-long immunity, and is typically the result of live immunizations.
The first live immunization was for smallpox, and was achieved by a very clever, and very simple trick. It was noted that milkmaids who got cowpox never got smallpox, so by giving cowpox to everyone, smallpox was eradicated. The Latin word for cowpox is vaccinia, and to give someone cowpox was to vaccinate them, the source of the word vaccine and vaccination. Technically to vaccinate someone only refers to preventing smallpox, which is why I use the word immunization.
The permanent protection against smallpox via vaccination was so effective that smallpox has been eliminated as a disease from the entire planet for over 40 years.
The next live immunization created was for polio. We are nearing the extinction of polio. Across the entire world in 2015, so far, only 26 cases of polio have occurred- 24 in Pakistan and 2 in Afghanistan. The virus is thought to still be alive in Nigeria as well. But that's it. India is now polio free for 3 years. The eradication of polio is close enough the US switched to the non-live form of polio immunization many years ago, so it is not a live vaccine in the US.
The three live viral immunizations we use routinely in Advanced Pediatrics are: the MMR, the varicella, and the influenza immunizations.
MMR
The MMR is the only form of immunization available in the US to prevent the infection measles. MMR stands for measles, mumps, and rubella. The MMR contains a very weakened version of all three of these viruses. Once placed in the body, each of these viruses replicate for a few cycles, die and are completely eliminated from the body. But, if the immunization works, if the body creates a response to these viruses, that leaves the body permanently protected.
For measles, the MMR works at least 95% of the time. That means if 100 people get 1 dose of the MMR, then 95 will not be able to get measles for the rest of their lives. For any individual that is pretty good level of protection, but in large groups, such as colleges, that still leaves about 1 in 20 able to sustain an epidemic. Hence the recommendation that everyone get two MMR's. The second dose may provoke permanent protection in some of the 5% who did not respond to the first dose.
So the second dose of the MMR is not a booster, it is simply a second chance to have a response.
We support the two dose strategy, it has worked well. Populations that have two doses of MMR do not have measles. Those that do not, do have measles.
I will also mention that the allegation that MMR can cause autism has been definitively disproven, and the intensity of belief in this idea has weakened dramatically in the last year or so.
Varicella or Chickenpox Immunization
Varicella is the Latin word for chickenpox, and zoster is the Greek word for shingles.
Varicella in Latin means little pox, since chickenpox is a lesser pox than smallpox. Zoster in Greek means belt, since the rash of shingles is often in a belt-like pattern.
The same virus causes chickenpox and shingles:
Herpes varicella-zoster. This is no surprise since shingles is simply the recurrence of chickenpox. The way it works is that if you get a case of chickenpox, the virus goes dormant in cells along your spinal cord the rest of your life. You won't get chickenpox again, but your own dormant chickenpox virus can re-activate and erupt down a nerve fiber from the spinal cord, appearing in a patch on the surface of the skin at the end of that nerve, hence the patch (shingle) or belt-like (zoster) of the rash.
The varicella or chickenpox (same thing) immunization is a live virus, and contains a very, very weak version of the living
Herpes varicella-zoster virus. One dose of this immunization renders nearly everyone permanently immune to severe chickenpox. If you've had only one dose and get exposed to a case of chickenpox, you have a 10% chance of developing chickenpox, but essentially all such cases are incredibly mild, with 1-10 red dots, and perhaps not even contagious. So, one dose nearly eliminates all chance of serious chickenpox disease permanently.
Since that protection is permanent like other live immunizations, there is no need for a booster.
But, a second dose is desirable to further reduce the chance of developing any chickenpox illness, even very mild, and thereby stopping the spread.
We support the recommendation that all children have two varicella or chickenpox immunizations prior to Kindergarten. For older youth and young adults who got their varicella or chickenpox immunization when it once was a one shot routine, the rationale for getting a second makes sense but is not urgent. Staying with one is a reasonable choice, and exposes the person to only the 10% risk of very mild cases of chickenpox.
The flu mist, or nasal influenza immunization
The third routine live immunization we recommend is the influenza immunization. It is the only nasal immunization we routinely offer. It works because the influenza virus naturally lives in the nose and so can do its work by nasal administration quite well.
If you have followed the difference between live and non-live immunizations, you might wonder, why is a live immunization like the nasal flu immunization given every year if live vaccines last all one's life and do not require boosters?
That would be a great question, and if you asked it you would be right, if you get a nasal flu immunization, your protected against those subtypes of influenza virus for life.
The problem is that the subtypes change every year, so last year's lifelong protection does nothing to protect against this year's viruses.
Not routinely used live vaccines
There are three other live immunizations that we do not use routinely that should be mentioned:
1. Polio- as noted above, live polio immunization is not used in the US, only the non-live version.
2. Typhoid- the oral typhoid immunization is used for those traveling outside of the US/Canada/Western Europe/Israel/New Zealand/Japan areas. This is the only live bacterial immunization we use in the office. It works because the typhoid germ naturally infects the gut, so it can be weakened to avoid causing illness and still administered orally and offer protection.
3. Rotavirus- this live oral immunization is also for a germ that infects the gut. We do not recommend its use for three reasons. First, the illness it prevents is harmless in the overwhelming majority of children in the US. Second, the immunization is associated with a small but measurable increase in the risk of causing intestinal obstruction. Third, the widespread use of this immunization has caused the number of rotavirus infections to go down, but another cause of viral stomach flu has taken its place, the noravirus, so this immunization program has had little impact on the chance of a child getting the stomach flu.
Bottom Lines
- Immunizations all work by getting the body to think a harmless version of a germ has caused a real infection, to lead to real protection from the real thing.
- Immunizations always contain the germ, in some the germ is not alive, in others it is.
- Non-living immunizations tend to offer protection that weakens over time, and so boosters are necessary to remain protected.
- Living immunizations tend to offer life-long protection, so boosters are not necessary, but more than one dose could be useful to improve the chance the immunization works, or to respond to a virus that changes type yearly.
- Details on living immunizations that we recommend are noted above.
To your health,
Dr. Arthur Lavin
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