Effectiveness and need for diphtheria, pertussis and tetanus vaccines

The most recent summary on the D/P/T vaccine was published by CDC in the MMWR of April 2018:

https://www.cdc.gov/mmwr/volumes/67/rr/pdfs/rr6702a1-H.pdf

There are graphs in the MMWR article showing how cases of all three diseases covered by the vaccine have changed over time.

These graphs show that there are almost no tetanus or diphtheria cases in the US now.  There were 2 diphtheria cases reported in the entire US between 2004 and 2016.*   While diphtheria can theoretically spread between people, it does not seem to do so in the US, presumably due to adequate herd immunity.

Tetanus is caused by bacteria that infect a wound or incision, form an abscess and produce a toxin that is a nerve poison.  Tetanus is a potentially life-threatening illness, but can usually be prevented by proper care of wounds.  There are about 30 cases and 1-6 deaths/year in the US from tetanus.* It does not spread from person to person.

Pertussis is a disease that looked like it, too was going to be nearly wiped out during the 1980s.  But the pertussis component of the (whole cell) DPT vaccine being used in those days was very toxic, causing many serious reactions and some deaths in infants and children.  So a newer, less toxic vaccine was introduced, DTaP.  This reduced the number of serious reactions, but the new vaccine was later discovered to be less effective at preventing pertussis than the old one. Per CDC:

"...reported rates of pertussis have been observed to be significantly lower among children who had started their vaccination series with DTP than among those who had started with DTaP (151,152)."

 In the approximately 23 years since its US introduction, pertussis cases have risen dramatically.  CDC says,

A growing body of evidence strongly suggests that the change in vaccines in the late 1990s from whole-cell pertussis vaccines to acellular pertussis vaccines in the childhood vaccine series has caused the age-specific increases in pertussis incidence among children aged 7–10 years observed in the mid-2000s because of waning immunity (Figure 2) (28–30).

The CDC decided to add another dose (the 6th dose) of a different DTaP vaccine (Tdap) at age 12, and uptake of this additional dose is at desired levels:

Since the introduction of Tdap in 2005, coverage with Tdap in adolescents aged 13–17 years has increased substantially, from 10.8% in 2006 to 86.4% in 2015 (33,34). Tdap coverage among adolescents has met the Healthy People 2020 target of 80% (35).

But Tdap vaccine did not provide the immunity boost CDC desired.  For the first year after a Tdap vaccination, effectiveness against pertussis is estimated about 67%, but by 4 years later effectiveness was only 9%.  The WHO says,

The disease, caused by the bacterium Bordetella pertussis, is endemic in all countries. Epidemic cycles have been occurring every 2 to 5 years (typically 3 to 4 years), even after the introduction of effective vaccination programmes and the achievement of high vaccination coverage.

In fact, it is possible that Tdap, or DTaP, actually increases susceptibility to pertussis.  According to pertussis expert Dr. James Cherry in 2019, because current acellular pertussis vaccines contain only a few antigens, "all children who were primed by DTaP vaccines will be more susceptible to pertussis throughout their lifetimes, and there is no easy way to decrease this increased lifetime susceptibility."   And according to pertussis studies performed by the FDA in baboons, those vaccinated with the current vaccine could still be infected with pertussis, and spread it for longer than baboons vaccinated with the older vaccine, and longer than unvaccinated baboons.

Most children who develop pertussis (80% in a Kaiser study) are fully vaccinated.  Herd immunity cannot be achieved due to poor effectiveness of current vaccines, even if 100% of the population is fully vaccinated.

Conclusion: 

Overall, children who lack DTap and Tdap vaccines pose no appreciable additional risk of infection to other children.  This is because there is virtually no risk of contracting diphtheria in the US, there is no person-to-person spread of tetanus, and current pertussis vaccines provide limited immunity but also the likelihood of enhanced spread.  These two effects likely balance out the transitory benefit of pertussis vaccination.


Meryl Nass, MD

  

*Centers for Disease Control and Prevention, Epidemiology and Prevention of Vaccine-Preventable Diseases, 13th Edition. Appendix E.

Babies get much higher doses of 

Diphtheria, Tetanus and Pertussis 

toxins in vaccines than adults!

	Tdap		DTaP
	Adults, Pregnant Women, 12 year olds		2, 4, 6 months 18 months 5 years
	Boostrix	Adacel	Infanrix	Daptacel
Tetanus Toxoid	5 Lf *	5 Lf	10 Lf	5 Lf
Diptheria Toxoid	2.5 Lf	2 Lf	25 Lf	15 Lf
Pertussis Toxin	8 mcg	2.5 mcg	25 mcg	10 mcg
FHA	8 mcg	5 mcg	25 mcg	5 mcg
Pertactin	2.5 mcg	3 mcg	8 mcg	3 mcg
Fimbriae protein    (types 2 & 3)	0	5 mcg	0	5 mcg
Aluminum Phosphate	-	+	-	+
Formaldehyde	+	+	+	+
Polysorbate 80	+	-	+	-
Aluminum Hydroxide	+	-	+	-
Glutaraldehyde	-	+	-	+
Phenoxyethanol	-	+	-	+
Pregnancy Category †	C	C	-	-

* Flocculating units

     ^† Risk not ruled out: "Animal reproduction studies have shown an adverse effect on the fetus and there are no adequate and well-controlled studies in humans, but potential benefits may warrant use of the drug in pregnant women despite potential risks."

    All information provided in the table comes directly from the label for each vaccine.  The label is a legal document specifying the use of the product, ingredients, and other information, which has been agreed through collaboration between the manufacturer and FDA/ 

   Table created by Meryl Nass, MD

FIGURE 2. Annual incidence* of pertussis, by age group — United States, 1990–2016

Sources: National Notifiable Diseases Surveillance System and Supplemental Pertussis Surveillance System.

* Per 100,000 population.