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How effective is Diphtheria vaccine?

According to the CDC, adults who receive three properly spaced diphtheria vaccines and infants who receive four, will develop antibodies considered protective against diphtheria approximately 95 percent of the time. The CDC also reports that the diphtheria vaccine has a 97 percent efficacy rate against clinical cases of diphtheria;  however they also state that “no randomized controlled clinical trial of the efficacy of diphtheria toxoid in preventing disease has ever been conducted”. 

Vaccinated individuals are still able to spread the bacteria because vaccination does not eliminate carriage of Corynebacterium diphtheriae in the back of the throat or on the skin.  

Between 2015 and 2018, an outbreak of diphtheria occurred in seven schools in Vietnam. Forty-six persons were diagnosed, and eight died. Vaccination status was not known for 85 percent of those affected; however, three of the eight who died had received at least two vaccine doses. Study authors expressed concerns that “Our finding of vaccinated people dying is particularly alarming because it might indicate a waning of vaccine-derived immunity.” 

A 2019 published review of diphtheria cases between 2000 and 2017 reported that 22 percent of cases occurred in fully vaccinated individuals and 13 percent among partially vaccinated individuals. This paper recommended that more emphasis was needed to ensure that children received the primary three doses of diphtheria and that adolescents and adults receive booster doses. 

Booster doses of diphtheria vaccine are recommended in the U.S. every 10 years;  however, a 2020 published study concluded that “Review of >11 billion person-years of incidence data revealed no benefit associated with performing adult booster vaccinations against tetanus or diphtheria.” 

IMPORTANT NOTE: NVIC encourages you to become fully informed about Diphtheria and the Diphtheria vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.

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