Safe and Effective Vaccine Against Yellow Fever

Yellow fever is a vector-borne viral hemorrhagic fever, which is transmitted by mosquitoes. This fever is common in South America and in sub-Saharan Africa. People travelling to endemic areas need to get vaccinated about 10-14days before their travel by the use of a live attenuated vaccine (17D). But there is a slight risk of the  vaccine virus replicating despite it being attenuated. If this happens then it poses certain risks of causing neurotropic adverse events and anaphylaxis that may sometimes result  in death. A need for safer vaccine has been explored in the last few years.   The answer maybe by using  a cell-culture vaccine that reduces the risk of allergic reactions replication. The vaccine can be administered to the elderly, immunosuppressed patients, infants below 9-months and even to pregnant and nursing women.

A cell-culture vaccine XRX-001 for yellow fever was tested  by scientists in 60 healthy individuals between 18-49 years of age. They studied the safety, adverse event profile and immunogenecity of the vaccine. The  XRX-001 is a whole virus β-propiolactone-inactivated yellow fever vaccine produced in Vero cell culture and adsorbed to 0.2% alum (aluminum hydroxide) adjuvant. It is manufactured by Xcellerlex. Subjects who qualified for the study were previously not vaccinated against  yellow fever, Japanese encephalitis or tick-borne encephalitis and nor did they have a history of overseas  travel to the tropics. Two shots of this vaccine which contained 0.48µg or 4.8µg antigen were administered intramuscularly 21days apart. Scientists then measured levels of neutralizing antibodies at baseline on days 0, 21, 31 and 42.

It was found that individuals who received 4.8µg of this inactivated vaccine induced development of neutralizing antibodies in 100% subjects and in 88% subjects who were administered 0.48µg of antigen.  Following the administration of the second dose the level of antibodies increased by day 10. This antibody level was significantly higher among individuals who received 4.8µg of the vaccine. No serious side-effects were reported except  for  pain, tenderness and itching at the injection site in some cases. Only 1 case of skin reaction (urticaria) was reported on day 3 after administration of 4.8µg of vaccine. The safety of the vaccine was assessed on the basis of local and systemic reactions.

Thus scientists concluded that this two-dose regime of the vaccine has the potential to be a safer alternative to the existing live attenuated vaccine (17D). This was the first clinical trial of the vaccine. A second clinical has to be initiated which would evaluate the durability of antibody response which has been reported in this trial.

Reference

Thomas P. Monath, M.D., Elizabeth Fowler, Ph.D., Casey T. Johnson, D.O., John Balser, Ph.D., Merribeth J. Morin, Ph.D., Maggie Sisti, B.S., and Dennis W. Trent, Ph.D.

New England Journal of Medicine 2011; 364:1326-1333April 7, 2011

Source-Medindia