A vaccine in development against the H5N1 influenza virus can produce a safe immune response in healthy people at low doses, according to an article published by The Lancet.

Vaccines that are effective at low doses are needed because they would allow more people to be immunised in the event of a pandemic.

Vaccines against pandemic influenza are being developed and clinically assessed by several drug companies throughout the world. In a previous trial published by The Lancet, scientists found that 30 (microgram) µg of a vaccine containing part of the H5N1 virus given in two doses with an adjuvant (an additive that can increase effectiveness) produced a good immune response in humans. However, a 30 µg vaccine that needs to be given in two doses may only provide enough vaccine for 225 million people under current manufacturing capabilities.

In the latest trial, Chinese researchers tested the effectiveness of a vaccine that contains a modified version of the whole H5N1 virus plus adjuvant. Vaccines made of whole viruses are known to trigger greater immune responses than those made out of virus particles, so lower doses may be effective. However, whole-virus vaccines are also known to have more sideeffects.

The investigators randomly assigned 120 volunteers aged 18-60 years to receive two doses of a placebo or the whole-virus vaccine at 1?25, 2?5, 5, or 10 µg doses plus the adjuvant aluminium hydroxide. After 56 days they found that all the formulations produced antibodies against the virus but the best response was seen in the 10 µg group after two doses. The 10 µg vaccine met all the European regulatory requirements for the licensing of an influenza vaccine. Pain, swelling, and fever were the most commonly reported side-effects in the trial. However, there was no difference in the frequency of reported side-effects between the vaccine and placebo group. The frequency of side-effects reported with the whole-virus vaccine was also similar to that seen with vaccines made out of virus particles.

Study author Weidong Yin (Sinovac Biotech co. Ltd, Beijing, China) states: “During a pandemic, the demand for influenza vaccines will far outstrip the manufacturing capacity of such vaccines, a situation that has led to WHO encouraging investigation into dose-sparing strategies, including the use of adjuvants and whole-virion vaccine. Our trial suggests that an H5N1 vaccine manufactured and formulated with both of these approaches is well tolerated and immunogenic.”

The authors say trials testing whole-virus H5N1 vaccine with adjuvant in larger numbers of individuals, including elderly and children, are needed.

http://www.thelancet.com/