Swine flu science update: 24 July 2009

People whose immune systems are suppressed by diseases such as HIV/AIDS are more likely to develop complications from influenza and should be vaccinated, a study has found.

The review of published research on the impact of influenza on people with underlying health problems was published in The Lancet Infectious Diseases this week.

The authors say that antiretroviral therapy decreases hospital admissions and deaths from influenza but acknowledge that only around ten per cent of people who need them receive antiretroviral drugs in the developing world.

They also say that while HIV patients may respond less effectively to an influenza vaccine, they can be safely vaccinated. This should inform vaccine policy, they say, though clinical trial data is sorely lacking.

The results of one such trial were presented at the 5th International AIDS Society Annual Meeting in Cape Town, South Africa, this week (22 July).

Around 500 HIV-positive patients in South Africa received either a seasonal influenza vaccine or a placebo before the onset of the flu season. Those receiving the vaccine experienced dramatically fewer influenza episodes than those on the placebo and the vaccine was 75 per cent efficient — similar to healthy patients. 

Whether people in developing countries get access to a vaccine could be down to whether the United States decides to use an adjuvant in vaccine formulations, according to Nature.

Adjuvants boost recipients' immune responses to a vaccine — thereby reducing the amount of virus protein required per dose and increasing the potential number of doses from 876 million to two billion annually — and the WHO has recommended their use. The Nature report describes the United States' decision as "imminent".

Statisticians trying to deduce how severe the swine flu pandemic will be say that usual methods of assessing severity may be inaccurate.

Fatality ratios for diseases are calculated by dividing the number of deaths by the number of cases — giving 0.5 per cent for influenza A(H1N1), similar to the upper range of that seen for seasonal influenza.

But this may not be appropriate for influenza A(H1N1), says a team from the UK-based Imperial College which published its research in the British Medical Journal last week (14 July).

The researchers say this is because many infections are not reported and some deaths are attributed to other causes. Also, ignoring the time lag between infection and death underestimates the severity in the initial stages and gives a false impression that the pandemic is getting more severe as time goes on. 

An article in the New England Journal of Medicine last week (16 July) tracks the genetic history of the virus back to the severe flu pandemic of 1918. The authors, from the University of Pittsburgh, describe a series of cross-transmissions between humans and pigs. They say emergence of "yet another" global health threat from animals highlights the critical need for a deeper understanding of animal viruses.

The British Medical Journal (BMJ) launched its pandemic flu site yesterday (23 July). It brings together the BMJ Group's free resources on influenza A(H1N1) including news, podcasts and clinical learning modules.