A vaccine in development against the H5N1 influenza virus can produce a safe immune response in healthy people at low doses, according to an Online/Article published today (Thursday September 7, 2006) 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 micrograms 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 microgram vaccine that needs to be given in two doses may only provide enough vaccine for 225 million people under current manufacturing capabilities (See accompanying Comment).
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 side-effects.
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 microgram 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 microgram group after two doses. The 10 microgram 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 place
Contact: Joe Santangelo