A new study from an Australian vaccine manufacturer suggests that just one shot of vaccine may produce a robust enough response in the immune system to protect people from being infected by the 2009 pandemic A/H1N1 swine flu virus. The news is expected to be welcomed by health authorities because it means more people can be protected more quickly as vaccine becomes available.

The study is the work of researchers at CSL Ltd, a global vaccine and plasma protein company with headquarters in Australia. In order to make the data available as quickly as possible, a preliminary version of the study is published in today’s issue of the New England Journal of Medicine, which also has reports of other swine flu vaccine studies.

The researchers report the early results of an ongoing trial that is evaluating a two-dose vaccine in healthy adults between the ages of 18 and 64 at a single site in Australia.

The findings suggest that one dose was enough to produce an immunogenic response, with “mild to moderate” side effects.

This is based on measures taken 21 days after the first of the two scheduled vaccine shots was given.

In a separate press statement CSL announced that:

“Over 95 per cent of participants receiving the single 15 mcg dose of the vaccine achieved antibody levels that correlate with the prevention of influenza infection.”

They also reported that the vaccine appears to have side effects similar to seasonal flu vaccines.

For the observer blind study, 240 healthy adults aged from 18 to 64 were treated at a single centre in Australia. They were randomly assigned into two different groups, each group being treated with a different dose of the vaccine.

Both groups received a first shot of vaccine followed by a second three weeks later. The first group had the standard 15 mcg dose and the second group had a 30 mcg dose. 15 mcg is the standard for a single strain in the seasonal flu vaccine, which usually contains vaccine against three flu strains.

All participants gave blood samples three weeks after each shot.

Preliminary results from the first shot show that:

  • By day 21 after vaccination, antibody titres of 1:40 or more were achieved in 96.7 per cent of participants (116 of the 120) who had the 15 mcg dose and 93.3 per cent of those (112 of 120) who had the 30 mcg dose.
  • This immune reponse was not age-dependent.
  • There were no deaths, or serious side effects, or side effects of “special interest” wrote the researchers.
  • The most commonly reported side effects were tenderness or pain at the injection site (46.3 per cent of subjects) and systemic symptoms like headache (45 per cent), and “nearly all events were mild to moderate in intensity”.

The authors concluded that:

“A single 15-mcg dose of 2009 H1N1 vaccine was immunogenic in adults, with mild-to-moderate vaccine-associated reactions.”

CSL Chief Scientific Officer Dr Andrew Cuthbertson told the media earlier today that:

“The preliminary data obtained from this initial study show a promising result which gives us confidence that a vaccination program can be successfully carried out in adults using a single standard dose of the H1N1 vaccine.”

Cuthbertson said the company was also conducting other studies examining how children and older adults respond to the vaccine.

“We look forward to sharing these data when they become available,” he added.

Cuthbertson said these results “provide critical information”, given that vaccine yields have not been as high as expected, and now, with these results showing that one shot is enough, the available vaccine will go much further.

Commenting on safety, Cuthbertson said that people should be assured that CSL found no safety signals so far in any of the current studies on the vaccine:

“We will, of course, continue to monitor safety through the clinical study process and with post-marketing surveillance,” he added.

Anthony S. Fauci of the National Institutes of Health, which is leading the American effort to develop an H1N1 swine flu vaccine told the Washington Post how he welcomed the good news:

“This is very good news. If you needed two doses, that would be a major strain on vaccine supplies nationally and globally.”

While not revealing any details, Fauci said the NIH was coming to similar conclusions in their own studies, which they hope to announce early results of later today.

Fauci said he expected that vaccines produced by the five companies making supplies for the US would be similar to the Australian one, implying that they also may produce a sufficiently robust response with only one shot.

There may still be groups, such as very young children, who will need two shots. Young children usually need two shots of seasonal flu because they have not been exposed to flu viruses before.

“Response after One Dose of a Monovalent Influenza A (H1N1) 2009 Vaccine — Preliminary Report.”
Greenberg, Michael E., Lai, Michael H., Hartel, Gunter F., Wichems, Christine H., Gittleson, Charmaine, Bennet, Jillian, Dawson, Gail, Hu, Wilson, Leggio, Connie, Washington, Diane, Basser, Russell L.
NEJM, Published online September 10, 2009.
DOI: 10.1056/NEJMoa0907413

Source: CSL Ltd, Washington Post.

Written by: Catharine Paddock, PhD