By Eduardo Gonzales, MD
Q—In the light of the Dengvaxia issue, I now wonder whether vaccines are safe or if they really work? What’s your take on this?
A—I don’t blame you for suddenly becoming skeptical about vaccines but offhand I can tell you that they work and that they are safe.
To understand how vaccines protect us, it is helpful to first look at how our body fights infections. When germs (disease-causing microorganisms) such as bacteria or viruses infect or enter our body, our body calls on an army of cells called lymphocytes to fight off the invasion. The lymphocytes produce weapons called antibodies, which are proteins that in so many ways are able to neutralize and kill the invaders. Unfortunately, the first time a specific agent, a mumps virus for example, enters our body, it takes some time (several days to a couple of weeks) for our lymphocytes to recognize it as a dangerous intruder and produce enough antibodies to eliminate it. Hence, we get sick, sometimes—if the microbe is really nasty like the measles virus or whooping cough bacteria—very seriously. If our lymphocytes are able to mount a counter-attack in time, we recover from our illness and as a bonus we get immune from subsequent infection by the same organism because in the aftermath of the initial infection, our lymphocytes, aside from producing antibodies also produced memory cells. These cells can immediately recognize the same microorganism should it infect us again and mount a massive and immediate counter attack (i.e., produce numerous antibodies) that will eliminate the invaders without us getting sick or even noticing we got infected.
HOW VACCINES WORK
A vaccine is a biological preparation that contains material that resembles a disease-causing microorganism such as a weakened or dead microbe, its toxins, or one of its surface proteins. The vaccine will not make us sick because it does not contain the disease-causing microorganism, but it tricks our lymphocytes into thinking it is a new invader and they react by producing antibodies to destroy it. They will likewise produce memory cells which will protect us against any future attack from the actual disease-causing organism that possesses the material that is in the vaccine.
HOW EFFECTIVE ARE VACCINES?
Vaccines definitely work in preventing many potentially fatal diseases, but not one is 100 percent effective. The efficacy of a vaccine depends on a number of factors: the microorganism itself (some vaccines perform better than others); our immune system, which sometimes does not respond adequately or not at all; and a host of other factors such as ethnicity, age, or genetic predisposition.
If a vaccinated individual, however, does develop the disease he/she was vaccinated against, the disease is likely to be less virulent than in unvaccinated patients. Vaccines mitigate an infection, resulting in a lower mortality rate, lower morbidity, and faster recovery.
The fact is vaccines are the most effective means to fight and eradicate infectious diseases. Widespread immunity due to vaccination (i.e., vaccine administration) has been primarily responsible for the worldwide eradication of smallpox and the restriction of diseases such as polio, measles, and tetanus from much of the world.
ARE VACCINES SAFE?
Like any medicine, vaccines are not 100 percent risk free, but scientific studies—such as the one published in the July, 2014 issue of the medical journal Pediatrics which reviewed 20,000 scientific titles and 67 papers on vaccine safety—consistently show that side effects of vaccines outside of soreness and redness at the injection site are extremely rare. Incidentally, the World Health Organization (WHO) reports that licensed vaccines are currently available for 25 different preventable infections.
There is no doubt that vaccines, especially those that have been widely-used for many years now are safe. Any licensed vaccine is rigorously tested for safety and efficacy across multiple phases of trials before it is approved for use, and once it is on the market, it is subjected to post-marketing surveillance, which aims to detect rare adverse effects as well as to assess long term efficacy. This meticulous post-marketing surveillance is the reason why Dengvaxia, a new vaccine, contrary to what its manufacturers claimed when it was released, was not effective in preventing dengue in all children, but only on those who have been previously infected with the dengue virus. Worse, Dengvaxia might even cause a more severe disease in those who have been immunized with the vaccine but where not previously naturally infected by the Dengue virus.
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