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Medical Health: Low dose human bird flu vaccines tests show it both safe and effective
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
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 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.
In an accompanying Comment Iain Stephenson (Leicester Royal
Infirmary, UK) states: "These findings identify a potential
dose-sparing approach that could be crucial for a global supply of
pandemic vaccine."
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