DTaP Vaccination Effectiveness Wanes With Time

The vaccine research group at Kaiser Permanente Northern California (KPNC) contributed another important article outlining the challenges of controlling pertussis in a highly vaccinated population, said Kathryn M. Edwards, MD, with the Vanderbilt University School of Medicine, in the June issue of Pediatrics. 

This new KPNC study found under-vaccinated and especially un-vaccinated children, were at greater risk of contracting pertussis. 

Of the 469,982 children in this study, 738 polymerase chain reaction–confirmed pertussis cases were diagnosed. 

Most of the pertussis cases occurred among children age-appropriately vaccinated but who had the most time away from their last diphtheria-tetanus-acellular pertussis (DTaP) vaccine dose. 

These researchers found the pertussis risk was 13 times higher among unvaccinated compared with fully vaccinated children and 1.9 times higher among under-vaccinated children. 

Among vaccinated children, the pertussis risk was 5 times higher 3 years or more after the last DTaP vaccination.

Among children ages 84 to 132 months, the risk of contracting pertussis was 2 times higher when the last dose was over 6 years vs 3 years after vaccination. 

This data suggests that suboptimal vaccine effectiveness played a major role in recent pertussis epidemics. 

‘Those individuals who began their medical career after 1997, when DTaP totally replaced conventional diphtheria, tetanus toxoids, and whole-cell pertussis (DTwP) vaccines, may question why DTaP replaced DTwP in the first place,’ said Dr. Edwards in a related commentary. 

‘The waning efficacy is likely because DTaP is an acellular vaccine, which replaced a whole-cell vaccine, DTwP, in 1997.’ 

Dr. Edwards explained that whole-cell vaccines generate more protective T-cell responses. 

Though more efficacious, the DTwP vaccine, which is not available in the USA, caused more negative reactions than the DTaP vaccine. 

According to the Centers for Disease Control and Prevention (CDC) vaccine schedule, the DTaP vaccine is given in 5 doses, between the ages of 2 months and 6 years. 

The CDC recently concluded the following assumptions:

• DTaP vaccine studies among Vaccine Adverse Event Reporting System (VAERS) reports found no health concerns related to the vaccine.
• Several studies of DTaP vaccine safety have looked for neurologic problems or seizures after children were vaccinated, and found that there is no increased risk for these concerns.
• DTaP may frequently cause mild injection site reactions.  However, severe reactions are rare, and may be less frequent when the vaccine is injected into the leg than into the arm.  Reactions happen about as often when DTaP is combined with other vaccines.
• The most common side effects are usually mild and go away on their own.
• Vaccines, like any medicine, can have side effects.

The CDC’s current estimate is that in the first year after getting vaccinated with Tdap, it protects about 70 percent of people who receive it.

And, there is a decrease in effectiveness in each following year. About 4 out of 10 people are fully protected 4 years after getting a Tdap vaccination.

Recent pertussis news:

• Montana's Pertussis Outbreak Reaches 14 Cases
• Which Vaccines Are Safe For Breastfeeding Women?
• Whooping Cough Vaccine Protection ‘Wanes’

As with any medicine, there is a very remote chance of a vaccine causing a severe allergic reaction, other serious injuries, or death. Serious reactions should be reported to the VAERS, says the CDC.

Your doctor will usually file this report, or you can do it yourself at the VAERS website.