Vaccines and virulence

Yesterday it was announced that Dr Michael Day, a GP from Bedfordshire, died from H1N1 influenza. A 6 year old girl has also died. Neither are believed to have had any serious underlying health problems

The news of a GP’s death will surely send a shudder down the spine of many healthcare workers. Should this be a wake up call for doctors to start taking this virus more seriously? Should doctors and others be taking more precautions than they are at present?

Coincidentally, the World Health Organisation announced yesterday that healthcare workers be prioritised above other at-risk groups to get the swine flu vaccine. This follows the most recent meeting of SAGE (the Scientific Advisory Group of Experts) on July 7th. The reasoning for prioritising healthcare workers is that they 1) put themselves at more risk of catching it; 2) they need to be in good health care for people with flu and 3) they need to care for people with other illnesses during the pandemic.

Another interesting issue to be discussed at the press conference was about the vaccine’s safety. Dr Marie-Paule Kieny, Director of the Initiative for Vaccine Research at WHO, was confident about the safety of the vaccines that have been developed but was keen to stress that any side effects must be carefully monitored. Could there be a risk of Guillain-Barre syndrome, as occurred following a similar vaccination program in 1976?

The vaccines which are produced now are much better purified than the way they were in 1976, so we really do not think that it is likely that we will have these side effects again, but to be absolutely honest, of course it is only when you have a large scale distribution of vaccines that you know with certainty the safety profile of the vaccine.

Reassuring? In addition, data seems to be thin on the ground in certain high risk groups who may be vaccinated as a priority:

“…safety data, at least in terms of numbers are lacking in certain population groups… certainly there are no data in children more than 6 months old and less than 3 years, there are no data in pregnant women, there are no data in asthmatics, so there are quite a number of populations for which there are no data. SAGE has also made the point that as quickly as possible data should be obtained on these populations groups if they are to be vaccinated with this new vaccines.”

Call of Nature

New research in Nature suggests that the new strain of H1N1 that’s causing swine flu (referred to in the paper as the CA04 isolate) is more virulent than seasonal influenza.

In mice and ferrets, CA04 and other S-OIV isolates tested replicate more efficiently than a currently circulating human H1N1 virus. In addition, CA04 replicates efficiently in non-human primates, causes more severe pathological lesions in the lungs of infected mice, ferrets and non-human primates than a currently circulating human H1N1 virus, and transmits among ferrets.

Data from the study suggests that it affects the lungs of mice, ferrets and non-human primates more severely than seasonal influenza.

In fact, the ability of CA04 to replicate in the lungs of mice, ferrets and non-human primates, and to cause appreciable pathology in this organ, is reminiscent of infections with highly pathogenic H5N1 influenza viruses… We therefore speculate that the high replicative ability of S-OIVs might contribute to a viral pneumonia characterized by diffuse alveolar damage that contributes to hospitalizations and fatal cases where no other underlying health issues exist.

They also provide evidence to explain why people in older age groups seem not to be as badly affected by swine flu.

The assessment of human sera from different age groups suggests that infection with human H1N1 viruses antigenically closely related to viruses circulating in 1918 confers neutralizing antibody activity to CA04.

Exposure to the flu in 1918 might explain a lower incidence in the over 90s, but why is swine flu so uncommon in the rest of the over-65 age group?
Tom Nolan is the clinical community editor of doc2doc, the BMJ’s professional networking community.