mmr shots

anonymous asked:

Scientifically speaking, why can't viruses be cured?

This depends on your definition of cure.

Many viruses can be prevented. Rotavirus, Polio, HPV, Varicella, Measles, Mumps, Rubella, Influenza, Hepatitis A & B can all be prevented with immunizations. However, many vaccinations are not 100% effective in preventing infection for two reasons: your personal immune system’s response to the vaccine, and mutation of viruses.

Your immune system, once exposed to a virus through infection or immunization, will create antibodies against a part of that virus (usually the envelope or shell of the virus). Over time, your antibodies may wane and you may be more susceptible to infection again. This is why we give booster vaccines, so that your immune system can “see” the invader again and bolster its defenses against it. For example, vaccination with one MMR shot offers 93% protection against measles, whereas protection goes to 97% with 2 shots.

Viruses also mutate (much like bacteria do when they become resistant to antibiotics) so that the body does not recognize them and attack with antibodies. They may also come in several common mutations or “strains,” so while you have immunity to one, you may be vulnerable to another. Some viruses mutate rapidly, like the flu, so we need repeat immunization against new strains and new mutations to keep up. 

We tend to only vaccinate against the most common strains of a virus too, which is why you can get the Gardasil shot for HPV (which covers types 6,11,16, and 18) and still contract a less virulent strain of the virus. These multiple strains and mutations are also why it’s very hard to make a medication for viral illnesses (and why Tamiflu’s efficacy is modest at best for treating the flu). By the time a drug is made, the virus has mutated and it doesn’t work anymore.

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Interesting

Med student meeting this morning before grand rounds with peds infectious disease doc.

He was telling us when he was in med school and residency in the 80s all the talk was about H. influenza, which now we rarely see because of the Hib vaccine.

And he brought up why there are multiple Hib and MMR shots on the schedule, asked us why. Although boosting titers is one reason, the main one is apparently that not everyone responds to the first vaccination with immune titer high enough to ward off infection. Everyone has a slightly different immunologic response and no vaccine is perfect.

In the case of measles, only 95% of people get high enough titers from the first shot, but measles needs 97% or higher for herd immunity to protect the immunocompromised. So, it is easier on children and the health system to give everyone two (or more in the case of other vaccines) childhood shots to ensure the levels of immunity in the population are high enough to keep measles outbreaks at bay.

This is actually something I have always wondered and no one ever had been able to answer, so I wanted to share!!