Thursday November 3 2011
The study did not find a new form of flu
A new strain of killer flu “could spread to Britain within 24 hours”, the Daily Express has today claimed. The Daily Mail also covered the story, reporting that research had found that people were infected with both seasonal flu and swine flu, sparking fears that the viruses could combine to form a “super-flu”.
The alarming reports in the Daily Mail and the Daily Express are rather misleading, for several reasons. The research the news was based on was actually a small, but important study that had examined a Cambodian patient who became unwell during the swine flu pandemic of 2009. Examining the man and four of his contacts, scientists determined that two of the five subjects were infected with both swine flu and a seasonal flu virus that was circulating in the environment at that time. None of the five infected individuals required hospitalisation and all made a full recovery.
This is valuable research in the light of the very real public health threat faced by flu pandemics; particularly as co-infection also offers the possibility for different viruses to combine their genetic material and produce new strains. However, such a ‘super-flu’ or ‘killer-flu’ has not been found, and is merely a possibility.
In the UK we are now entering the flu season. People who are most vulnerable to the effects of flu will be offered a jab against seasonal forms of flu. The composition of this jab is based on predictions of which predominant strains will circulate, and it will be designed to protect against multiple strains - even swine flu if it is likely to circulate.
Where did the story come from?
This research was carried out by scientists from the Naval Health Research Center, California; US Naval Medical Research and the National Institute of Public Health, Kingdom of Cambodia; and the J. Craig Venter Institute, Maryland. The study was funded by the US Department of Defense Armed Forces Health Surveillance Center division of the Global Emerging Infections Surveillance and
Response System; the US Defense Advanced Research Projects Agency; and the National Institute
of Allergy and Infectious Diseases, National Institute of Health, Department of Health and Human Services.
The study was published in the peer-reviewed American Journal of Tropical Medicine and Hygiene.
Although news coverage has reflected the findings of this study accurately and quoted flu experts, the overall emphasis of reports has been misleading and alarmist. Their headlines suggest that a “deadly super flu” has been found and is ready to spread to the UK. This is not the; these are laboratory findings from five people infected in 2009 with swine flu and/or seasonal flu. None had severe illness or required hospitalisation, and none died from a ‘deadly new super-flu’.
What kind of research was this?
This paper is a case series which reports on a man from Cambodia infected with a particular form of ‘swine flu’ virus during the early months of the 2009 pandemic. It reports on an influenza-like illness that developed in four of his contacts. Scientists analysed samples taken from these subjects to look at the viruses that they were infected with. They used genetic analysis to see how these viruses were related to those circulating in the environment at the time.
A study of this type provides scientific and medical information on the clinical characteristics of infected individuals. It also gives valuable insights into viral strains circulating in the environment. However, it should be noted that this study examined a very small sample of individuals and therefore from this limited analysis we do not know how many other individuals during the 2009 outbreak would have been dually infected with two flu viruses; or whether this co-infection may have caused serious illness in others.
What did the research involve?
The A/H1N1 influenza virus (pH1N1), commonly known as swine flu, emerged in Mexico in 2009 and quickly spread globally. This study reports on a 23-year-old man living in central Cambodia in October 2009 who presented himself to doctors with a temperature of 39ºC, and symptoms of headache, sore throat and cough and generally feeling unwell. Genetic analysis of samples taken revealed that he was infected with the swine flu virus. A similar influenza-like illness subsequently developed in three children who lived in his home and the children’s school teacher. Specimens were also taken from these four individuals for genetic analysis.
What were the basic results?
Of the four contacts, one of the children and the teacher were infected with both a seasonal form of flu (A/H3N2) and the swine flu (pH1N1) viruses. Further analysis of genes from these viruses showed that the two viruses were closely related to the pH1N1 and A/H3N2 viruses currently circulating in the region. The two remaining children were infected with only the seasonal influenza A/H3N2.
In the samples from the two dually-infected individuals, there was no evidence that the two viruses had combined their genetic material. These dually-infected individuals did not seem to be more seriously ill than those individuals infected by a single virus.
None of the five infected individuals required hospitalisation for their illness. Four were treated with antibiotics (one received no treatment), and all five made a full recovery.
How did the researchers interpret the results?
The researchers conclude that their findings confirm that “dual influenza virus infections” have occurred. This highlights the risk that people could become simultaneously infected with seasonal influenza viruses and zoonotic influenza viruses (i.e. those that cross between animal species, such as ‘swine’ flu and ‘bird’ flu). It is possible that the two viruses could combine their genetic material to produce a new strain of flu, but this was not observed in the people in this study.
These findings present a cluster of five people who developed influenza-like illness in central Cambodia in 2009. The first case was affected with swine flu; two with seasonal flu; and two with both seasonal and swine flu. The researchers say that finding of co-infections has rarely been reported, and that prior study of more than 2,000 clinical samples had found no dual infection. However, they say that other isolated cases of co-infection with swine flu (pH1N1) and seasonal flu A/H3N2 have been reported in individuals from Singapore, China and New Zealand.
This new evidence that co-infections are possible is a valuable discovery There is the possibility that when two viruses infect an individual, they might have the ability to combine their genetic material and produce a new more virulent strain. Importantly, this has not been demonstrated to have happened as yet. However, when looking solely at the information from the current study of only five individuals, it is not possible to know what proportion of those infected during the 2009 swine flu pandemic, or since, may have been dually infected. It also does not tell us whether dual infection could affect the severity of the illness in some individuals. In this case, all five infected individuals made a complete recovery, and none needed to be hospitalised.
Also, none of the five patients in this outbreak had been vaccinated against either seasonal or pH1N1 influenza infections, as seasonal vaccination in this rural region is rare. It is possible that where seasonal vaccination is offered to vulnerable individuals, as it is in the UK, the risk of dual infection might be reduced.
The ‘24 hour’ implication reported in the news follows a statement by Dr Peter Hotez, president of the American Society of Tropical Medicine and Hygiene, which published this study. Dr Hotez praised the discovery and said that “highly infectious strains of the virus against which humans have little defence can spread from one continent to another within 24 hours”. He highlighted the need for extra vigilance following the discovery of the potential for ‘double-flu’ infection. This view is endorsed by the researchers who note “the importance of national and international co-operation to survey for the emergence of novel and/or reassorted influenza viruses”. As yet, no combined strain has been identified.
In the UK we are now entering the flu season and the predominant strains that will affect people this winter remain to be seen. Seasonal flu jabs will have been produced based on predictions of what strains are likely to be circulating.