oseltamivir (tamiflu) and zanamivir (relenza), the two anti-virals known to be effective, must be taken within 48 hours of onset of symptoms or earlier to be effective; the positive effects are greatest if treatment is started within six hours. the hpa reported in its 24 june 2009 weekly epidemiological report that all 17 samples of the virus laboratory tested for resistance that week were found to be sensitive to oseltamivir and zanamivir, but resistant to amantadine. the first case of resistance of the virus to oseltamivir, in denmark, was reported on 29 june 2009. on 5 may 2009 plans were announced for pupils unable to sit examinations at schools affected by flu to be assessed in other ways to ensure that children are not disadvantaged. the department of health has listed all the pandemic flu guidance that it had published as of 8 june 2008. genetic analysis samples from suspected cases have been analysed by the national institute for medical research in london, which is also examining samples of the u.s. strain of the disease. by 8 may 2009 the us centers for disease control and prevention had made genetic information on the swine flu virus available, and the virus from european samples had been isolated and its full genetic fingerprint determined by uk researchers. the genetics and effects of the virus in general are discussed in the article on the 2009 swine flu pandemic. diagnosis the fastest way for laboratory confirmation of swine flu is by the pcr method, described as a real-time method. according to the world health organization there are four laboratories in the uk able to perform pcr to diagnose influenza a (h1n1) virus infection in humans: regional virus laboratory, royal victoria hospital, belfast, ni; regional virus laboratory, gartnavel general hospital, glasgow, scotland; health protection agency, centre for infections, enteric, respiratory, & neurological virus laboratory, london; who collaborating centre for reference and research on influenza, national institute for medical research, london. another laboratory confirmation is a fourfold increase in virus-specific antibodies 10 to 14 days later. from 2 july 2009 when a treatment, rather than containment, approach was adopted, the official clinical diagnostic criteria became: "fever (pyrexia ≥38 °c) or a history of fever, and also influenza-like illness (two or more of the following symptoms: cough; sore throat; rhinorrhoea; limb or joint pain; headache; vomiting or diarrhoea) or severe and/or life-threatening illness suggestive of an infectious process". "laboratory confirmed" cases professor neil ferguson, an epidemiologist at imperial college london, who advises the government and the world health organization, said on 8 june 2009 that hpa statistics were at best accounting for half of cases. in the usa mathematical modelling based on surveys estimated that there were about 1 million cases of h1n1 flu on 25 june 2009, compared to 28,000 reported officially. such a study has not been carried out in the uk. as of 2 july 2009 gps will diagnose based on clinical observation and routine swabbing will stop, and the hpa will "no longer be providing a daily update of the numbers of cases confirmed through laboratory tests" hygiene recommendations according to the health protection agency's "swine flu: frequently asked questions" web page, transmission of this new virus is thought to occur in the same way as seasonal flu: large droplets from coughing and/or sneezing by an infected person within a short distance (usually 1 metre or less) of someone; touching or shaking the hand of an infected person, and then touching your eyes, nose or mouth without first washing your hands; touching surfaces or objects (e.g. door handles) that have become contaminated with the flu virus, and then touching your eyes, nose or mouth without first washing your hands. when the issue of touching your eyes, nose or mouth is combined with other infection control practices and good hygiene measures as recommended by the health protection agency's website, the following recommendations emerge as important ways to help reduce the spread of swine flu and other viruses: don't touch your eyes, nose or mouth without first washing your hands. cover your nose and mouth when coughing or sneezing, and use a tissue when possible. dispose of dirty tissues promptly and carefully. maintain good basic hygiene, for example washing hands frequently with soap and water to reduce the spread of the virus from your hands to your face, or to other people. clean hard surfaces, such as door handles, frequently using a normal cleaning product. make sure children follow this advice. anyone with swine flu or being investigated as a possible case will be given anti-virals and asked to stay at home and limit their contact with other people. where anti-virals are prescribed the course of treatment must be followed and completed, although it may sometimes cause nausea. for people belonging to a high-risk group it is particularly important that they start taking anti-virals as soon as possible after infection. high-risk groups include people with long-term conditions, those over 65, children under five and pregnant women. immunity a study at the u.s. centers for disease control and prevention published in may 2009 found that children had no pre-existing immunity to the new strain but that adults, particularly those over 60, had some degree of immunity. children showed no cross-reactive antibody reaction to the new strain, adults aged 18 to 64 had 6–9%, and older adults 33%. the large proportion of cases in the uk affecting children and young adults is consistent with this pattern of resistance. vaccine main article: 2009 flu pandemic vaccine the usual seasonal flu vaccines gave little or no immunity against the new strain of flu. there was an international program to produce a vaccine which would be effective against the new h1n1 strain. the chief medical officer sir liam donaldson said on 25 june that it seemed likely that the uk would receive the first batches of vaccines slightly earlier than expected, possibly from august rather than the autumn as first expected, although some industry sources do not expect supplies to be available so soon. the government had contracts for 132 million doses. there were risks involved in shifting resources to the new vaccine: it would not be possible to produce the seasonal flu vaccine, and it was possible that the virus will mutate to make a vaccine developed before the mutation ineffective. possible use of face-masks alan johnson, health secretary at the time of the outbreak the then health secretary alan johnson told mps on 27 april that "although we are aware that face-masks are being given out to the public in mexico, the available scientific evidence does not support the general wearing of face-masks by those who are not ill, whilst going about their normal activities." professor steve field, chairman of the royal college of general practitioners, said people in the uk were "perfectly safe at the moment", and did not need to start wearing face-masks or stop eating pork. the head of pandemic planning at the royal college of general practitioners, dr maureen baker, stated on 27 april that "masks become ineffective when they become damp or after a few hours. there has been a lot of debate on the use of face-masks and some authorities say that, in the community, the most effective use is to give to patients who may have symptoms when they present in the surgery – that should help reduce the infectivity of that patient to surgery staff and other patients. i expect the department of health will issue guidance on use of face-masks if we move into a pandemic phase." masks may not protect the wearer from inhalation of the virus, but might protect other people from picking up the virus from the wearer. professor john oxford, a virologist at leading london hospital, the barts and the london, said: "really, there is very little evidence that masks actually offer much protection against flu." it was reported that the uk government was urgently seeking to acquire more face-masks. the advice given by authorities in several countries on the use of face masks has been summarised in an article, with many references, published on 4 june 2009. aside from their obligations under health and safety legislation, employers can help to minimise the spread of the virus and support good infection control practice by positively encouraging any employee who reports feeling unwell with influenza-like symptoms to stay at home until their symptoms resolve, by sending people home who develop influenza-like illness at work (avoiding public transport and wearing a face mask if possible) and by ensuring that stocks of surgical face-masks are available in the workplace for symptomatic staff to wear until they get home.— doh pandemic flu plan, november 2007