The Vaccine-Preventable Diseases

Critica Continues the Series About What We Are Vaccinating Against

Part Two: DTaP

With so much news and comment about the hoped-for vaccine against the virus that causes Covid-19, we continue to believe that some general information about vaccines might be helpful. Last month we described the MMR vaccine and the diseases it prevents (measles, mumps, and rubella). This month we tackle another trivalent vaccine—a vaccine that works against three different diseases—the DTaP vaccine. That stands for diphtheria, tetanus, and acellular pertussis (the version for people older than seven years is called TDaP and is sometimes referred to as the booster version).

         The DTaP vaccine (which some may remember as the DPT vaccine) is one of the most important standard vaccinations given to children, adolescents and adults. It has saved the lives of countless people around the world because each of the three illnesses the DTaP vaccine prevents is fully capable of causing death.

         The CDC recommends that the DTaP vaccine be given to babies in four doses between two and 15-18 months. A fifth dose is recommended between four and six years and a dose for adolescents at 11-12 years.  For children who did not receive the vaccine as infants, there is a schedule of recommended catch-up vaccination times in childhood and adolescents. CDC further recommends TDaP as follows:

Pregnant women should get a dose of Tdap during every pregnancy, to protect the newborn from pertussis. Infants are most at risk for severe, life-threatening complications from pertussis.

Adults who have never received Tdap should get a dose of Tdap.

Also, adults should receive a booster dose every 10 years, or earlier in the case of a severe and dirty wound or burn.  Booster doses can be either Tdap or Td (a different vaccine that protects against tetanus and diphtheria but not pertussis). However, see later for some other ideas about this.

Like all vaccines, DTAP, TDaP, and Td can cause pain and soreness at the injection site. More serious reactions range from 1 in 10,000 children to the pertussis portion of the vaccine to one in a million children to the tetanus portion. Death associated with DTaP is extremely rare and generally believed by experts to be coincidental rather than caused by the vaccine.

We will now review each of the three illnesses this vaccination prevents.


         Tetanus is sometimes referred to as “lockjaw” because it usually involves the tightening of the jaw and month due to severe, involuntary muscle contraction. Muscle spasms then spread through the body, which can cause fractures and tendon injuries. People with tetanus can get pneumonia, blood clots in the lungs, nerve injuries, and several other complications and can lapse into a coma. Although most people survive tetanus, recovery can take several months and the mortality rate from severe tetanus is about 50%.

This man has the typical muscle contractions that come with tetanus, which is why it is sometimes referred to as “lockjaw” (source: CDC).

Tetanus usually begins with a wound, often an innocuous one like a simple cut or puncture wound. Most times, the individual does not even feel the need to seek medical treatment. But the bacteria that causes tetanus, clostridium tetani, lurks everywhere and can enter the wound, take hold, and release two powerful toxins that cause the disease. These bacteria are an example of what are called anerobic bacteria, meaning that they live without oxygen and therefore can survive underneath the skin or deep in tissues.

         In the U.S. today, most cases of tetanus and most deaths from tetanus occur in people who have never been vaccinated. The vaccine has dramatically decreased the incidence of tetanus in the developed world, but it still kills many people worldwide in places where vaccination rates are low.

         Because the bacteria that cause tetanus do their damage via the toxins they secrete, the tetanus vaccine is designed to stimulate immunity against the toxin itself. This involves taking the toxin and chemically inactivating it to a form that cannot cause illness. An inactivated toxin is called a “toxoid.” When the tetanus toxoid is injected, the immune system recognizes it as a foreign invader and develops immune memory so that if the vaccinated person is later actually infected with the tetanus bacteria, antibodies will immediately be produced to destroy the toxin and prevent disease.

         This might be a good opportunity to reiterate that despite the fact that children now receive many vaccines according to the recommended CDC schedule, they do not “overwhelm” the immune system and render it unable to fight other diseases. The immune system operates by developing cells and antibodies that are highly specific to each individual disease-causing agent. The antibodies against tetanus toxins involve a miniscule portion of the human immune response capacity and have no implications for the ability to fight other diseases.


         Diphtheria is one of those diseases that is so rare today because of vaccination that some people may think it doesn’t exist any longer. Unfortunately, the bacteria that causes diphtheria, Corynebacterium diphtheriae, does still exist and without vaccination, diphtheria cases will return. Jack remembers an unvaccinated child with diphtheria in the pediatric intensive care unit when he was a pediatric intern in the 1970s. The child developed a dread heart complication and died.

         Diphtheria starts with what seems like a fairly ordinary upper respiratory infection but can quickly progress to difficulty swallowing and obstruction that causes difficulty breathing. As with tetanus, these complications are caused by a toxin released by the bacteria (actually by a virus that infects the bacteria). If that bacteria enters the blood circulation, it can cause a type of heart muscle damage called myocarditis and also nerve damage. About 5-10% of people with diphtheria die, a figure that rises to 20% among children under five and adults over 40.

This child is very ill with diphtheria, with typical sore throat and swollen glands that can progress to difficulty swallowing and breathing and heart muscle and nerve damage. Vaccination has almost entirely eliminated diphtheria in the U.S. (source: CDC).

         Please remember those statistics. One in five children under five will die if they get diphtheria; the vaccine extremely rarely if ever causes death and the serious complications that can occur in about 1 in 10,000 children who get the whole DTaP vaccination are mostly temporary.

         Again like tetanus, the vaccine against diphtheria is aimed against the toxin that causes the illness. A chemically inactivated version of the toxin, called the diphtheria toxoid, is injected and this stimulates memory in the immune system, making it prepared to fight an actual infection if that ever happens. Complications from diphtheria toxoid itself are mild, such as pain at the injection site and occasionally low-grade fever.

Pertussis (Whooping Cough)

         Although once again the incidence of pertussis, or whooping cough, has dramatically decreased since vaccine introduction, it is still a cause of infant death around the world and cases have been increasing steadily in the U.S. since the 1980’s. Half of babies who develop pertussis require care in the hospital and 1-3% under three months die. It is spread in much the same way as the virus that causes COVID-19—by droplets from coughing and sneezing. But unlike COVID-19, a person exposed to pertussis bacteria is virtually guaranteed  (80-90%) to get the illness. Also, unlike COVID-19, pertussis is caused by bacteria, called Bordetella pertussis, and not a virus.

         There are three stages of pertussis infection, each lasting up to six weeks. The first signs that an infant, child, or adult has contracted pertussis is usually a seemingly ordinary upper respiratory infection with stuffy, runny nose and sneezing. This is the catarrhal phase. Next comes the much more serious paroxysmal phase in which a severe cough lasting several minutes develops. The cough is often followed in babies over 6 months by a loud whooping sound. During these episodes of coughing, a baby can be unable to breath and become exhausted. Broken ribs and burst blood vessels in the eyes have occurred because of the paroxysmal coughing. Pneumonia can develop. This is the phase in which deaths can occur. It is clearly not an ordinary cold or even the flu, but a life-threatening event that is painful to watch.

This child with pertussis (whooping cough) has broken blood vessels in his eyes and bruising on his face due to the severe coughing that is part of the illness. In babies, this coughing can lead to periods of lack of oxygen, putting the child’s life at risk (source: CDC).

         For survivors of the paroxysmal stage there is the convalescent stage, with cough lasting for weeks.

         Once again, the culprit in pertussis is not the bacteria themselves but five toxins they produce. The vaccine, therefore, is aimed at producing immunity against the toxins. The newest version of the pertussis vaccine was introduced in 1996 and is called the acellular vaccine. The older version contained killed whole virus and caused a significant number of adverse side effects, including seizures with high fever in one in 1,750 doses. The newer version does not contain whole killed virus but rather only some inactivated bacterial proteins and has a much lower rate of complications (about 1 in 10,000 serious complications, including high fever, seizures, inconsolable crying, and a syndrome in which the child becomes listless and lethargic with poor muscle tone for several hours). But immunity from the acellular vaccine may wane over time. Just as it is currently recommended that adults get tetanus and diphtheria boosters (called Td vaccine) every 10 years, some experts now recommend that pertussis vaccine be added to those boosters in the form of the TDaP vaccine.

         Our hope in bringing you this series to you is that it will remind all of us that vaccine-preventable diseases are rarely seen today only because the vaccines against them are so effective. They are by no means eradicated and unless most members of a community are vaccinated, epidemics of them will certainly return. You will hear people tell stories about horrid complications from vaccines and make claims that they harm the immune system and can even be lethal. We do not deny the fact that in extremely rare cases vaccines may cause serious complications and we have been careful to outline them here.

For every story you hear about a child who has allegedly been harmed by a vaccination (and we say allegedly because many of them turn out to be coincidences), we could tell you a million stories of children who have no serious complications and because of vaccines can live lives free of some of the most horrible disease known.

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