This article is more than 5 years old. Information may no longer be current.

Fractional dose of yellow fever vaccine confers long-term immunity

Administration of a one-fifth dose of yellow fever vaccine resulted in long-term protection against the virus, according to data published in Annals of Internal Medicine.

“Outbreaks of yellow fever and a frequently depleted vaccine stock increase demand for a dose-sparing strategy,” Anna H.E. Roukens, MD, PhD, from the Leiden University Medical Center, the Netherlands, and colleagues wrote. “A fractional dose of 17D yellow fever virus (17D-YFV) vaccine has been shown to be noninferior to the standard dose in inducing seroprotection.”

Roukens and colleagues performed a 10-year follow-up analysis of a randomized, controlled, noninferiority trial to determine if a fractional-dose vaccine provides long-term immunity of yellow fever.

The researchers evaluated a subgroup of patients from the trial who provided a blood sample and received primary vaccination with 17D-YFV vaccine 10 years prior (n = 75). Among these participants, 40 received a 0.1 mL fractional dose intradermally and 35 received the standard 0.5 mL dose subcutaneously. The researchers used a plaque reduction neutralization test to measure virus-neutralizing antibody responses.

Data showed that a majority of participants who received a fractional dose of 17D-YFV vaccine (98%; 95% CI, 89-100) demonstrated seroprotection from yellow fever–neutralizing antibodies more than 10 years after receiving the vaccine. This protection was similar to that of participants who received the standard dose of the vaccine — 97% (95% CI, 87-100) of whom indicated protective levels against the virus.

Most virus neutralization (80%) occurred at a reciprocal geometric mean titer of 54 (95% CI, 40-68) in participants receiving the fractional dose and 55 (95% CI, 40-70) in those receiving the standard dose.

“This study and the one by de Menezes Martins and colleagues are, to our knowledge, the first ones to document long-term protection after fractional-dose yellow fever vaccination,” Roukens and colleagues concluded. “These findings reinforce the policy of using fractional doses in preventive mass vaccination campaigns before an impending outbreak and show that a booster dose of 17D-YFV vaccine is not necessary after receipt of a fractional dose.” – by Alaina Tedesco

Disclosures: The authors report no relevant financial disclosures.