A/H1N1 influenza: questions and answers

BMJ 2009; 338 doi: http://dx.doi.org/10.1136/bmj.b1849 (Published 07 May 2009) Cite this as: BMJ 2009;338:b1849
  1. Rebecca Coombes, associate editor, BMJ
  1. rcoombes{at}bmj.com

    The pandemic alert level has been raised to phase 5—just one level short of a full pandemic—by the World Health Organization. As influenza A/H1N1 spreads quickly from its origins in Mexico, Rebecca Coombes assesses the threat and our levels of protection

    What is pandemic flu?

    The term pandemic relates to the virus’s geographical spread rather than its severity. A flu pandemic is an ongoing worldwide epidemic caused by a novel influenza virus that infects a large proportion of people lacking immunity to that virus. It is at this point that the World Health Organization raises its alert level to 6. The three flu pandemics of the 20th century were in 1918, 1957, and 1968. The current phase 5 is characterised by “human to human spread of the virus into at least two countries in one WHO region”—a strong signal that we are on the brink of an epidemic and that the time to finalise plans is short.

    Is it too late to stop a pandemic?

    Richard Coker, professor of public health at the London School of Hygiene and Tropical Medicine, said in a BMJ editorial on 30 April that containment is probably not feasible, given the widespread presence of the virus across many countries (BMJ 2009;338;b1791, doi:10.1136/bmj.b1791). So far, cases are occurring in countries with robust surveillance systems. He pessimistically wonders if this is because cases are not coming to light in countries with poorer surveillance systems. Are we seeing only a part of the global picture? It is harder for developing countries to detect and mitigate the effects of a new flu virus, because they have low or nonexistent stocks of antivirals and limited access to an effective vaccine once it is produced.

    How severe is this flu? How does it compare with seasonal flu?

    The situation is unpredictable, and it is dangerous to second guess what might happen next. So far the case fatality rate is unknown. Each year seasonal flu kills around 250 000 to 500 000 people around the world. However, A/H1N1 is a novel combination of viral strains never seen before; and because humans don’t have natural immunity to it (unlike with seasonal flu) the disease has spread quickly. In the event of an epidemic in the United Kingdom, authorities are expecting to see an attack rate of 70% in children under the age of 12 months and between 35% and 50% in adults.

    It’s too early to say whether some age groups are more at risk. In Europe, confirmed cases are mainly among adults aged less than 50 years old, possibly reflecting the age profile of people travelling to Mexico. Until the virus starts to spread widely in countries outside Mexico it would be premature to characterise the epidemic in terms of attack rate and age distribution. Despite the several deaths in Mexico and one in the United States, symptoms in most people have been relatively mild so far.

    What is different about A/H1N1 flu?

    Swine flu is a highly contagious acute respiratory disease of pigs, caused by one of several influenza A viruses. So far three type A flu virus subtypes have been found in pigs: H1N1, H1H2, and H3N2. The Mexican virus is of the H1N1 family, named after its two surface proteins. Mortality in pigs tends to be low (1-4%). Human infection with swine flu has been detected occasionally since the late 1950s, usually among people working with pigs, but secondary cases after human to human transmission have been very rare. The A/H1N1 virus has been found to contain a unique combination of genes from pig, bird, and human flu viruses. Infections from human to human have been occurring for the past three weeks, at least.

    What do you do if a patient phones up the surgery with suspected swine flu?

    The algorithm from the Health Protection Agency (which was last updated on 30 April at time the BMJ went to press) guides clinicians on which patients should be treated with antivirals (www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1240732819361). You should take precautions if faced with a patient with a febrile respiratory illness who had travelled to an area of the world affected by influenza A/H1N1 in the seven days before the onset of symptoms. Doctors should assess patients at home, if possible, or at least away from communal areas. The patient should wear a facemask, and staff should wear facemasks, plastic aprons, and gloves. The local health protection unit (see www.hpa.org.uk) should be informed immediately, and nose and throat swabs should be sent for testing. Treatment with an antiviral should be started as soon as possible. Unless ill enough to require admission to hospital, patients should be advised to stay at home until test results are available. This entire procedure changes if the situation shifts up to a pandemic (WHO alert level 6).

    What are the arrangements for administering antivirals in the event of a pandemic?

    The National Flu Line—flagged as the main route for the public to get advice and access to antivirals during a pandemic—won’t be available until the autumn. The contract is in place; but meanwhile GPs and NHS Direct are being told to muddle through. “We were 98% ready, but unfortunately this flu has come just too early,” said an insider. So if a pandemic is announced, the only route for patients to access antiviral drugs will be through NHS Direct, which will use an algorithm to determine whether a caller has influenza A/H1N1. These patients will then get an authorisation number from NHS Direct for the drugs and must send a “flu friend”—an uninfected person—to an approved pick-up point to collect them. The aims are to promote self care and to keep infected people at home if possible, away from general practices and hospitals.

    Is it worth wearing a facemask?

    A systematic review last year (BMJ 2008;336:77-80, doi:10.1136/bmj.39393.510347.BE) showed that many simple and low cost interventions in healthcare settings, including facemasks, could help to reduce the spread of respiratory viruses. Masks can be simple and need not be of the N95 type (respirators with a 95% filtration capability). It’s worth remembering that ordinary surgical masks become sodden within about an hour and a half, so clinicians would have to change masks about six times a day if they wanted to wear a mask continuously. Although most surgeries and hospitals will have stocked up on gloves, masks, and gowns, supplies are limited, so it is best to use them only when around affected patients.

    There is no convincing scientific evidence that the widespread use of facemasks by members of the public can stop the disease spreading. They can give false reassurance and may encourage people to ignore basic hygiene measures that have proven effectiveness.

    What can we learn from the SARS epidemic?

    Six case control studies cited in the 2008 systematic review referred to above assessed the effect of public health measures to curb the spread of the epidemic of severe acute respiratory syndrome (SARS) in China, Singapore, and Vietnam in 2003. The data indicate that setting up barriers to transmission, isolation measures, and relatively cheap hygiene interventions—hand washing more than 10 times daily, wearing N95 masks, wearing gloves and gowns, or a combination—are effective in containing epidemics.

    How can people best protect themselves?

    There is good evidence on how patients can protect themselves (see previous answer). Frequent hand washing (more than 10 times a day) is the key to reducing risk. There is no evidence that medicated soaps are better than ordinary soap. People should cover their nose and mouth when coughing and sneezing, use tissues, and dispose of tissues promptly and carefully. The virus can live outside the body for up to four hours; the Department of Health advises cleaning hard surfaces with a normal cleaning product.

    How effective are the antiviral drugs?

    If taken within 48 hours, neuraminidase inhibitors such as zanamivir (Relenza) and oseltamivir (Tamiflu) halve the rate of excretion of the virus and reduce the duration of infection by just over a day (Cochrane Database of Systematic Reviews 2006;(3): CD001265, doi:10.1002/14651858.CD001265.pub2). This means that patients who take these drugs will be less likely to infect someone else, but they do not prevent infection in the first place. The authors of the Cochrane review also caution: “We are unsure of the generalisability of our conclusions from seasonal to pandemic or avian influenza.” Japan, which consumes 60% of the world’s oseltamivir, warned in 2007 that the drug should not be prescribed to teenagers because it could led to bizarre behaviour. In Europe doctors are advised that psychological disorders have been reported in Japan. Oseltamivir is currently available online in the UK for nearly 10 times its retail price of £16.36 for a pack of 10 capsules.

    Should staff be given oseltamivir?

    GPs are concerned about the health of their teams and have asked whether antivirals should be provided for staff to take. The BMJ understands that plans to offer prophylactic antivirals to frontline clinical staff are under urgent discussion. One practical difficulty is that staff would be required to take the drug for many weeks. Healthcare staff should not presume to be deemed the highest priority: water, sewerage, and power workers are likely to come first, followed by tanker drivers and food distribution workers.

    Does last year’s flu vaccine work against A/H1N1?

    There are similarities between the usual H1N1 human flu viruses, which the vaccine protects against, and swine flu, so there may be some level of cross protection, but this is likely to be partial. No information exists at present indicating that the seasonal flu vaccine offers any protection, and further investigations will take some time.

    What is the expected pattern of spread of this virus?

    Usually the pattern of spread of human flu viruses depends on where in the world they occur. The UK is now coming out of the winter flu season into a drier, less humid period, which suppresses the transmission of flu. In tropical regions outbreaks can occur throughout the year. It remains to be seen whether or not A/H1N1 will defy this seasonal trend. In the UK, if flu continues to spread, there will be a need to prepare very hard for a resurgence in September, October, and November.

    How soon will a vaccine be available?

    The procedure for creating a vaccine is straightforward, but it will take up to six months to get a product into industrial production and available for mass use. The factories that make regular human flu vaccine have the capability to rapidly manufacture vaccines for a pandemic, and the Department of Health has contracts with two manufacturers. The US Centers for Disease Control and Prevention hopes to produce a reference strain to send to manufacturers by the second week of May. Once the UK Health Protection Agency receives samples of the virus, the process can begin here.

    Should I recommend travel to the affected areas of Mexico and the US?

    Advise patients to check the continually updated advice on the Foreign and Commonwealth Office website (www.fco.gov.uk/en/travelling-and-living-overseas/swine-flu).

    Where should I go for updated information?

    Check the BMA website daily (www.bma.org.uk/health_promotion_ethics/influenza/index.jsp), and click through from here to the relevant sites, such as those of the Health Protection Agency, WHO, and the Department of Health. The Royal College of General Practitioners is issuing daily email newsletters.


    Cite this as: BMJ 2009;338:b1849


    • Sources: World Health Organization, BMA, Health Protection Agency, Royal College of General Practitioners, Department of Health, European Centre for Disease Prevention and Control.