New Yellow Fever Vaccine Shows Comparable Efficacy to Standard Vaccine

The phase 2 randomized controlled trial, published in *The New England Journal of Medicine*, evaluated the immunogenicity and safety of vYF compared to YF-VAX. The study enrolled 568 healthy adults aged 18 to 60 years across 11 centers in the United States. Participants were randomized in a 2:1 ratio to receive either vYF or YF-VAX.

The primary endpoint was seroconversion at day 29 among participants with no prior yellow fever infection or vaccination. The results showed that seroconversion occurred in 99.7% of participants in the vYF group and 99.4% in the YF-VAX group, demonstrating noninferiority.

Neutralizing antibody geometric mean titers rose substantially by day 29 in both groups and remained above the protective threshold in more than 97% of both groups at 1 year. Solicited adverse events were similar between the two groups, with headache and injection-site pain being the most common.

This new vaccine, vYF, uses a live-attenuated approach, similar to the existing vaccine, but is grown in Vero cells, a cell line that allows for more efficient production and higher yields. This is particularly important in addressing vaccine supply shortages experienced during previous outbreaks, such as the one in Angola and the Democratic Republic of the Congo between 2015 and 2016.

The vYF vaccine has demonstrated comparable efficacy and safety to the YF-VAX vaccine in clinical trials.

The vYF vaccine can be produced more efficiently and in higher yields, which can help address vaccine supply shortages during outbreaks.

The vaccine is intended for individuals living in high-risk areas and travelers heading to these areas, as recommended by the World Health Organization.

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