Though some consider the precautionary measures taken during the H1N1 swine flu epidemic to have been excessive, ‘better safe than sorry’ was an understandable position for health officials to take.
That stance is justified to some degree by the results of a study published today in PLoS Medicine. The analysis of the first few months of the epidemic in Vietnam suggests that actions taken in Ho Chi Minh City probably bought healthcare services valuable time to build up their response.
The researchers, from the Wellcome Trust Major Overseas Programme and Oxford University Clinical Research Unit at the Hospital for Tropical Diseases in Vietnam, analysed records from the 2009 strain of influenza virus A (H1N1) cases from the Ministry of Health, the Hospital of Tropical Diseases and the healthcare services of Ho Chi Minh City.
This produced a dataset of 321 people who tested positive for H1N1 and 298 people who tested negative between May and July 2009. The researchers say this represents 76 per cent of the known cases in southern Vietnam at the time.
Their analysis confirmed that the effects of H1N1 at the time were largely mild. Encouragingly, most cases responded well to treatment with the flu drug oseltamivir – the average time from starting treatment to completely clearing the virus was between 2.6 and 2.8 days (for those who began treatment 1-4 days after they became ill).
However, the study indicated that containing the epidemic in Ho Chi Minh City was never an achievable goal. Vietnam reported its first case of infection on 31 May 2009 and despite containment measures it had spread throughout Ho Chi Minh City by the second half of July. As of February 2010 there had been over 11,000 confirmed cases in Vietnam, including 58 confirmed deaths.
Yet the measures taken weren’t totally in vain. When the World Health Organisation declared a Phase 4 risk of a pandemic on 27 April 2009, the Vietnamese Ministry of Health mandated body temperature scans and questionnaires about symptoms for international travellers arriving at Ho Chi Minh City airport. Any suspected cases were quickly isolated in hospital.
Between 27 April and 24 July 2009 around 760,000 passengers who entered the airport on international flights were screened (0.15 per cent of incoming passengers). In the two months between 26 May and 24 July, this identified 200 positive cases among passengers.
According to the study, the intervention strategies shortened the amount of time infected individuals spent in the community, helping reduce the chances of transmission. The researchers also estimate that one in six passengers on incoming flights would have heard announcements suggesting self-quarantine, mask wearing, and guidelines for monitoring personal health. This increased the likelihood of people taking up hygienic behaviour and reporting if they had influenza-like symptoms.
“The containment measures seemed to delay the onset of large-scale transmission by at least three weeks,” said Dr Maciej Boni, one of the researchers from the University of Oxford.
“This may not sound like a lot, but in a country like Vietnam this bought valuable time for the local health services, laboratories and travel authorities to understand what was happening and start logistical preparations for the pandemic response.”
The researchers warn against reading too much into the results in terms of predicting the success of similar measures against future pandemics.
“The problem is that you don’t know what kind of virus you’re dealing with at the moment that measures need to be installed,” said Dr Rogier van Doorn of the Oxford Unit, who led the study.
“For a different type of virus, it will depend what we turn out to be dealing with. Human H5N1 bird flu cases are usually very severe, but not very transmissible, so they are easy to find and contain, and our strategies of drug treatment, contact tracing, isolation, poultry vaccination seem to have made such outbreaks manageable so far.”
The researchers are hesitant to put too much weight behind their findings. They point out that the study is largely based on observational data that is also incomplete. In addition, the patients studied were not randomised and some of the data from different sources are not directly comparable as they use different definitions. It’s also hard to assess the impact of intervention measures quantitatively without knowing how much of the virus was circulating among asymptomatic patients or how much the containment measures cost.
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