Swine influenza 2009

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Swine influenza 2009 is now officially known as A(H1N1)pmd(09) (A(H1N1)pdm09) and was known as Influenza (pandemic (H1N1) 2009) as a general term and for individual isolates influenza A(H1N1)v [1]

Swine flu resulted from reassortment in various host animals producing a strain that resulted in a pandemic in 2009. The strain also produced an impact during the influenza seasons of 2010 in countries such as New Zealand and the UK with unvaccinated at risk younger patients continuing to get seriously ill[2]. Avian influenza is still available for reassortment. By August 2010 WHO reported that 18,449 deaths had been notified worldwide[3]. The pandemic phase officially finished on 10 August 2010[4].

Contents

Background

Swine Flu - a form of H1N1 influenza A normally only affecting pigs - was reported in Mexico and some states of the USA in spring 2009. This strain of flu made the transition to sustained human transmission which made a human pandemic likely. There was no human vaccine against this strain during the first wave; however it did respond to antivirals (oseltamivir (2.5% of tested 2009 pandemic influenza A(H1N1) viruses were resistant) and zanamivir (no resistance), but not amantadine/rimantadine). This was thought to offer the opportunity for more successful containment and treatment over that existing with previous potential pandemic influenza situations. School closure and isolation strategies were also used. Establishing a lag into a full pandemic was postulated to allow vaccine development before drug resistance developed. Oseltamivir ring prophylaxis did work in Singapore army camps . The Mexican first wave has now been described with its bell shaped curve suggesting a delaying strategy using measures more usually used as part of a containment strategy worked to some degree[5].

Haemagglutinin genetic drift from data submitted up to 26th May with Swine influenza outbreak 2009

Features

  • Transmissability and rates of viral shredding were similar to seasonal influenza A
  • Age specific recognised attack rate in Mexico constant at about 2.5 per 100 000 population till sudden fall age 60 to 0.6 per 100,000[6] The full epidemiology confirmed that those born while the 1918 pandemic virus was circulating were protected.
Age distribution in UK[7]
Age Infection attack rate 95% CI
<1 year 14.5% 6.6 to 31.5%
1-4 years 22.7% 9.9 to 62.3%
5-14 years 29.5% 16.9 to 64.1%
15-24 years 10.9% 6.3 to 27.1%
25-44 years 8.2% 3.7 to 24.7%
45-64 years 6.4% 2.3 to 22.9%
65+ years 0.8% 0.2 to 4.9%
  • Incubation 1-8 days
  • Fever (94%), cough(92%), sore throat(66%), diarrhoea(25%), vomiting(25%), also rhinorrhea, headache and myalgia[8].
  • Infective phase may be for 12 hours before clear symptom onset to end of symptoms.
  • Mexico mortality was 2% of confirmed cases with 29% of the deaths with underlying metabolic disease[5]. This was an overestimate of the potential mortality due to case ascertainment issues, with for example Japan having less than 1 death per 1000 cases[9]. Mortality rate was higher in those with a specific haemagglutinin mutation (HA1 D222G) in Norway[10]. This single nucleotide mutation was not associated with any mild cases and subsequently this finding was confirmed in other international studies.
  • The at risk population includes the immunocompromised, those with chronic disease and pregnant. Outside recognised risk groups for pandemic influenza more severe illness has been reported in very obese males.
    • Pregnant women accounted for 5% deaths, but are only 1% of population
    • Retrospectively it has been shown that both vaccination early in pregnancy and treatment on symptoms (not based on serology or vaccination status) reduces mortality[11]
  • Other associations possibly associated with more severe disease include raised creatine kinase and thromboembolic pulmonary embolism[12].
  • Basic reproductive rate (Ro) probably 1.4 to 1.6 with effective reproductive number sometimes above 2 and 30% clinical attack rate reasonable assumption[13]

Note, however, that there may be some systematic biases to the above reports. Few cases are tested unless they meet criteria, such as the UK's S5 algorithm:[14] and to qualify, the patient has to have a fever and flu like illness. It is possible that not everybody with swine flu has a fever, for example - and indeed, some reports suggest that this is likely[15]with several patients being asymptomatic after post exposure prophylaxis but the virus has been isolated from them[16]. Such patients would be easily missed, meaning that case-finding is biased towards identifying cases with a fever.

Diagnosis

RT-PCR of upper airway swap specimens has the highest specificity and sensitivity (98%), closely followed by viral culture. Influenza antigen and direct fluorescent antibody testing for influenza A are known to have lower sensitivity (60%)[17].

Early time course

First wave epidemics became established during April to June 2009 in Mexico, and the USA, and in May to July 2009 in Canada, Australia, NZ, Chile, Argentina and UK as well as probably the rest of the Americas and much of South East Asia. Some countries such Spain and South Africa escaped true epidemic first waves at this time, with South Africa's first wave developing in August. Viral influenza isolate patterns in the Southern hemisphere were over 90% of this virus subtype during their usual seasonal flu season while Northern hemisphere isolates ran more like 60%. Japan which could be expected to have had very high accurate case ascertainment had over 5000 confirmed cases without a death by the end of July 2009 but had several deaths in August (10) with evidence that its seasonal flu peak was likely to occur early, by late September. Germany appears to have had even higher ascertainment likelihood with 16835 confirmed cases and no deaths to end of August 2009. The UK had had 13192 confirmed cases with 70 deaths by September 2009 but had long given up routine confirmation testing, actually about the time of its first wave peak at the end of July. Deaths in Mexico had reached 199 by September 2009. A pattern of very high pressure on intensive care facilities during peak activity had been established in the first world, with suspected much higher mortality rates and pressures on the full health care system in the third world countries as activity peaked there.

Confirmed data on 2009 H1N1 outbreak initiated in Mexico

  • Base line situation: Phase 3 for both Avian and Swine flu strains, with more serious avian cases worldwide.
  • 10 March Symptom onset of earliest (retrospective) proven human case [18].
  • 18 March Surge of influenza like illness in Mexico, starting around La Gloria, most in retrospect another strain but 5 cases confirmed (later).
  • 1 April First specimen that turns out to be of new flu subtype taken as as part of a clinical trial in San Diego County[8]. First (spanish) media reports of outbreak.
  • 12 April First extra territorial notification by Mexico of a respiratory illness outbreak in Veracruz
  • 13 April First possible flu death in Oaxaca state
  • 15 April CDC identifies novel flu type: A/California/04/2009[8].
  • 17 April Second specimen of novel flu type received by CDC from Imperial County, California and same day notification to WHO[8].
  • 21 April CDC reports 2 isolated cases of novel swine flu in California
  • 23 April Mexico City has had 854 cases of pneumonia with 59 deaths
  • 24 April 12 of Mexico outbreak cases found to be identical
  • 25 April WHO declares public health emergency of international concern as result of 7 cases of Swine Influenza A/H1N1 in USA
  • 26 April 20 cases to date confirmed in USA, 18 cases to date Mexico. Many more cases suspected but there is a lag of several days for full confirmatory tests to be done and Mexican confirmations have to be done in Canada due to USA biosecurity rules.
  • 27 April WHO phase 4, new cases confirmed to date: Mexico (26 - 7 deaths), USA (40), Canada (6), Spain (1)
  • 28 April New cases confirmed to date: Mexico (26 - 7 deaths), USA (64), Spain (2), NZ (3), UK (2), Israel (2)
  • 29 April WHO phase 5, 148 cases, new confirmed to date: Mexico (26 - 7 deaths), USA (91 - 1 death), Canada (13), Spain (4), Germany (3), Austria (1).
  • 30 April 257 cases, new confirmed to date: Mexico (97 - 7 deaths), USA (109 - 1 death), Canada(19), Spain(13), UK (8), Switzerland (1), Netherlands (1)
  • 1 May 367 cases, new confirmed to date: Mexico (156 - 9 deaths), USA (141 - 1 death), Canada (34), NZ (4), Germany (4), China-Hong Kong (1), Denmark (1)
  • 2 May 658 cases, new confirmed to date: Mexico (397 - 16 deaths), USA (160 - 1 death), Canada (51), UK (15), Germany (6), Republic of Korea (1), Italy (1), France (2), Costa Rica (1). Also found in swine herd in Alberta as a result of human transmission from Mexico.
  • 3 May 898 cases, new confirmed to date: Mexico (506 - 19 deaths), USA (226 - 1 death), Canada (85), Spain (40), Germany (8)
  • 4 May 1085 cases, new confirmed to date: Mexico (590 - 25 deaths), USA (286 - 1 death), Canada (101), Spain (54), NZ (5), UK (18), Israel (4), France (4), Colombia (1), El Salvador (2)
  • 5 May 1490 cases, new confirmed to date: Mexico (822 - 29 deaths), USA (403 - 1 death), Canada (140), Spain (57), UK (27), Germany (9), Republic of Korea (2), Italy (5), Ireland (1), Portugal (1)
  • 6 May 1893 cases, new confirmed to date: Mexico (942 - 29 deaths), USA (642 - 2 deaths), Canada (165), Spain (73), UK (28), Denmark (1), France (5), Sweden (1), Guatemala (1)
  • 7 May 2371 cases, new confirmed to date: Mexico (1112 - 42 deaths), USA (896 - 2 deaths), Canada (201), Spain (81), UK (32), Israel (6), Germany (10), Republic of Korea (3), Poland (1).
  • 8 May 2500 cases with 46 deaths, new confirmed to date: Mexico (1204 - 44 deaths), USA (896 - 2 deaths), Canada (214), Spain (88), UK (34), Israel (7), Germany (11), Netherlands (3), France (12), Brazil (4).
  • 9 May 3440 cases with 49 deaths, new reported to 06:00 with 48 deaths. Mexico (1364 - 45 deaths), USA (1639 - 2 deaths), Canada (242 - 1 death), NZ (7), Italy (6), Brazil (6), Panama (2), Japan (3)
  • 10 May 4379 cases, new reported to 07:30: Mexico (1626 - 45 deaths), USA (2254 - 2 deaths), Canada (280 - 1 death), Spain(93), UK (39), Israel (7), Italy (9), Costa Rica (8 - 1 death), Panama (3), Japan (4), Australia (1), Argentina (1).
  • 11 May 4694 cases with 53 deaths, new reported to 06:00: Mexico (1626 - 48 deaths), USA (2532 - 3 deaths), Canada (284 - 1 death), Spain (95), UK (47), China (2), Italy (9), France (13), Colombia (3), El Salvador (4), Sweden (2), Brazil (8), Panama (15), Norway(2).
  • 12 May 5251 cases with 61 deaths, new reported to 06:00. Mexico (2059 - 56 deaths), USA (2600 - 3 deaths), Canada (330 - 1 death), UK (55), Germany (12), Panama (16)
  • 13 May 5728 cases with 61 deaths, new reported to 06:00: USA (3009 - 3 deaths), Canada (358 - 1 death), Spain (98), UK (68), China (3), Colombia (6), Panama (29), Finland (2), Thailand (2), Cuba (1).
  • 14 May 6497 cases with 65 deaths, new reported to 06:00: USA ( 3352 - 3 deaths), Canada (389 - 1 death), Spain (100), UK (71), China (4), France (14), Colombia (7).
  • 15 May 7520 cases with 65 deaths, new reported to 06:00: Mexico (2446 - 60 deaths), USA ( 4298 - 3 deaths), Canada (449 - 1 death), France (14), Colombia (10), Panama (40), Cuba (3), Belgium (1).
  • 16 May 8451 cases with 72 deaths, new reported to 07:00: Mexico (2895 - 66 deaths), USA ( 4714 - 4 deaths), Canada (496 - 1 death), NZ (9), UK (78), Germany (14), Colombia (11), Costa Rica (9 - 1 death), Guatemala (3), Panama (43), Ecuador (1), Peru (1).
  • 17 May 8480 cases with 72 deaths, new reported to 06:00: Spain (103), UK (82), China (5), Sweden (3), Panama (54), Japan (7), Belgium (4), India (1), Malaysia (2), Turkey (1).
  • 18 May 8829 cases with 74 deaths, new reported to 06:00: Mexico (3103 - 68 deaths), UK (101), China (6), Japan (125), Belgium (5), Turkey (2), Chile (1).
  • 19 May 9830 cases with 79 deaths, new reported to 06:00: Mexico (3648 - 72 deaths), USA (5123 - 5 deaths), UK (102), China (7), El Salvador (6), Panama (59), Japan (159), Peru (2), Chile (4).
  • 20 May 10243 cases with 80 deaths, new reported to 06:00: USA (5469 - 6 deaths), Spain (107), France (15), Colombia (12), Poland (2), Panama (65), Japan (210), Peru (3), Chile (5), Greece (1).
  • 21 May 11034 cases with 85 deaths, new reported to 06:00: Mexico (3892 - 75 deaths), USA (5710 - 8 deaths), Canada (719 - 1 death), Spain (111), UK (109), China (8), Italy (10), France (16), Costa Rica (20 - 1 death), Guatemala (4), Panama (69), Japan (259), Australia (3), Norway (3), Cuba (4).
  • 22 May 11168 cases with 86 deaths, new reported to 06:00: USA (5764 - 9 deaths), Spain (113), UK (112), China (11), Panama (73), Japan (294), Australia (7), Ecuador (8), Peru (5), Chile (24).
  • 23 May 12022 cases with 86 deaths, new reported to 06:00: USA (6552 - 9 deaths), Spain (126), UK (117), Germany (17), Switzerland (2), Italy (14), Panama (76), Japan (321), Australia (12), Norway (4), Belgium (7), Taiwan (1), Russia (1).
  • 24 May No WHO update
  • 25 May 12515 cases with 91 deaths, new reported to 06:00 (no report 24 May): Mexico (4174 - 90 deaths), Canada (805 - 1 death), Spain (133), UK (122), Israel (8), Switzerland (3), China (15), Italy (19), Colombia (13), Costa Rica (28 - 1 death), Poland (3), Brazil (9), Japan (345), Australia (16), Argentina (2), Ecuador (10), Peru (25), Chile (44), Honduras (1), Iceland (1), Kuwait (18).
  • 26 May 12954 cases with 92 deaths, new reported to 06:00: USA (6764 - 10 deaths), Canada (921 - 1 death), Spain (136), UK (137), China (20), Republic of Korea (21), Colombia (16), Costa Rica (33 - 1 death), Japan (350), Australia (19), Argentina (5), Ecuador (24), Peru (27), Chile (74), Philippines (2), Russia (2)
  • 27 May 13398 cases with 95 deaths, new reported to 06:00: Mexico (4541 - 83 deaths), Spain (138), Israel (9), China (22), Italy (23), El Salvador (11), Guatemala (5), Japan (360), Australia (39), Argentina (19), Ecuador (28), Chile (86), Taiwan (4), Bahrain (1), Singapore (1).
  • 28 May No WHO update
  • 29 May 15510 cases with 99 deaths, new reported to 06:00: Mexico (4910 - 85 deaths), USA (7927 - 11 deaths), Canada (1118 - 2 deaths), Spain (143), UK (203), Israel (11), Germany (19), Switzerland (4), China (30), Republic of Korea (33), Italy (26), France (21), Colombia (17), Ireland (3), Sweden (4), Poland (4), Brazil (10), Panama (107), Japan (364 ), Australia (147), Argentina (37), Finland (3), Belgium (8), Ecuador (32), Peru (31), Chile (165), Greece (3), Philippines (6), Taiwan (9), Singapore (4), Romania (3), Czech Republic (1), Dominican Republic (2), Uruguay (2), Slovakia (1).
  • 30 May No report from WHO although ECDC reports 17232 cases with 115 deaths and fair number new cases in Australia and Europe
  • 31 May No report from WHO although ECDC reports 17395 cases with 115 deaths
  • 1 June 17410 cases with 115 deaths, new reported to 06:00: Mexico (5029 - 97 deaths), USA (8975 - 15 deaths), Canada (1336 - 2 deaths), Spain (178), UK (229), Israel (19), Germany (28), Switzerland (8), China (52), Italy (29), France (24), Colombia (20), Costa Rica (37 - 1 death), El Salvador (27), Ireland (4), Guatemala (12), Brazil (18), Japan (370 ), Australia (297), Argentina (100), Belgium (12), Ecuador (39), Peru (36), Turkey (4), Chile (250), Greece (4), Philippines (16), Taiwan (12), Russia (3), Honduras (2), Singapore (5), Uruguay (11), Slovakia (2), Bahamas (1), Hungary (1), Cyprus (1), Bolivia (3), Estonia (1), Jamaica (2), Paraguay (5), Venezuela (2), Viet Nam (1).
  • 2 June 19159 cases with 117 deaths reported to ECDC
  • 3 June 19273 cases with 117 deaths new reported to 06:00: USA (10053 - 17 deaths), Canada (1530 - 2 deaths), Spain (180), NZ (10), UK (339), Israel (33), Switzerland (10), Netherlands (4), China (69), Republic of Korea (41), Italy (30), France (26), Costa Rica (50 - 1 death), El Salvador (41), Portugal (2), Guatemala (14), Sweden (7), Brazil (20), Panama (155), Japan (385), Australia (501), Argentina (131), Finland (4), Belgium (13), Peru (40), Chile (313), Greece (5), Taiwan (14), Singapore (9), Romania (5), Dominican Republic (11), Uruguay (15), Venezuela (3), Viet Nam (3), Bulgaria (1), Egypt (1), Lebanon (3), Nicaragua (1).
  • 4 June 21823 cases with 125 deaths reported to ECDC
  • 5 June 21940 cases with 125 deaths reported to 06:00: Mexico (5563 - 103 deaths), USA (11054 - 17 deaths), Canada (1795 - 3 deaths), Spain (218), NZ (11), UK (428), Israel (39), Germany (43), Austria (2), Switzerland (10), Netherlands (4), China (89), Denmark (4), Republic of Korea (41), Italy (38), France (47), Colombia (24), Costa Rica (68 - 1 death), El Salvador (49), Ireland (8), Portugal (2), Guatemala (23), Sweden (13), Poland (4), Brazil (28), Panama (173), Japan (410), Australia (876), Argentina (147), Norway (9), Finland (4), Thailand (8), Cuba (4), Belgium (13), Ecuador (43), Peru (47), India (4), Malaysia (2), Turkey (8), Chile (369 - 1 death), Greece (5), Philippines (29), Taiwan (16), Russia (3), Honduras (34), Iceland (1), Kuwait (18), Bahrain (1), Singapore (12), Romania (8), Czech Republic (2), Dominican Republic (33), Uruguay (15), Slovakia (3), Bahamas (1), Hungary (3), Cyprus (1), Bolivia (3), Estonia (3), Jamaica (2), Paraguay (5), Venezuela (3), Viet Nam (3), Bulgaria (1), Egypt (1), Lebanon (3), Nicaragua (5), Barbados (1), Luxembourg (1), Saudi Arabia (1).
  • 6 June 25026 cases with 139 deaths reported to ECDC
  • 7 June 25643 cases with 139 deaths reported to ECDC
  • 8 June 26035 cases with 139 deaths reported to ECDC
  • 9 June 26744 cases with 140 deaths reported to ECDC
  • 10 June 27737 cases with 141 deaths reported to 06:00 to WHO
  • 11 June WHO phase 6 (Pandemic). 29254 cases with 144 deaths reported to ECDC
  • 12 June 29837 cases with 145 deaths reported to ECDC
  • 13 June 36389 cases with 164 deaths reported to ECDC
  • 14 June 36864 cases with 165 deaths (1st UK death) reported to ECDC
  • 15 June 37479 cases with 165 deaths reported to ECDC
  • 16 June 39260 cases with 168 deaths reported to ECDC
  • 17 June 41586 cases with 176 deaths reported to ECDC
  • 18 June 42224 cases with 175 deaths reported to ECDC (one US notification withdrawn)
  • 19 June 44287 cases with 180 deaths reported to WHO or 44605 cases with 181 deaths reported to ECDC
  • 20 June 50914 cases with 228 deaths reported to ECDC
  • 21 June 51702 cases with 230 deaths reported to ECDC
  • 22 June 52160 cases with 231 deaths reported to WHO or 52962 cases with 232 deaths reported to ECDC
  • 23 June 54934 cases with 239 deaths reported to ECDC
  • 24 June 55867 cases with 238 deaths reported to WHO or 56129 cases with 249 deaths reported to ECDC
  • 25 June 59179 cases with 258 deaths reported to ECDC
  • 26 June 59814 cases with 263 deaths reported to WHO or 68096 cases with 306 deaths reported to ECDC
  • 27 June 69839 cases with 312 deaths reported to ECDC
  • 28 June 71578 cases with 320 deaths reported to ECDC
  • 29 June 70893 cases with 311 deaths reported to WHO or 73153 cases with 324 deaths reported to ECDC
  • 30 June 76229 cases with 330 deaths reported to ECDC
  • 1 July 77201 cases with 332 deaths reported to WHO
  • 2 July 81700 cases with 339 deaths reported to ECDC. UK moves to mitigation & treatment phase
  • 3 July 89921 cases with 382 deaths reported to WHO or 90852 cases with 384 deaths reported to ECDC
  • 16 July WHO reports "In past pandemics, influenza viruses have needed more than six months to spread as widely as the new H1N1 virus has spread in less than six weeks". 128,273 cases with 679 deaths reported to ECDC. However in one reporting country with good community surveillance, the UK, 55,000 new cases estimated in last week when only 10,649 confirmed including 29 deaths in that week (and only 17 of those deaths in the report to ECDC figure)
  • 6 August 2010 WHO reports 18,449 deaths had been notified worldwide with 491,382 cases notified as serology positive[3] The pandemic phase ended officially on 10th August 2010[4].

The plot above starts on 15th April 2009 and from July shows increasingly incomplete data as reporting changed. UK suspected data was not published from 15/6/09 and from 17/6/09 clinically presumed cases presumably diagnosed in retrospect by resolved symptoms were reported. From 25/6/09 Scotland stopped reporting clinically presumed cases. UK data was no longer issued on a daily basis on from 2/7/09 but case ascertainment was probably fair up until the second week of June at least and is likely to be as good data as any other nation could offer at close to real time. Issues such as case ascertainment policies, resources to do this and use of virus detection verus antibody detection mean that this data simply gives a feel for what was really happening. For example UK and Australia by the beginning of July were reporting very similar numbers of confirmed cases but the Australian number of deaths were 3 times higher from effectively identical start times. The most likely explanation is better initial case ascertainment in the UK due mainly to seasonal factors forcing Australia to move to the mitigation and treatment phase much sooner than the UK. The death rate is probably lower than 1 per 1000 infected with fully functioning health care systems in the first epidemic wave but is more than 0.5 per 1000. While unexceptional death rates for a epidemic it as atypical as it is much more biased towards younger adults than seasonal influenza and is certainly the fastest spreading pandemic in history by an order of magnitude. The excess mortality of the 1918 (second wave) pandemic might only be three times greater assuming only half the population were infected then[19]. There is nothing particularly reassuring in the data to hand compared to say the 1957/58 pandemic as already by July southern hemisphere countries are noting heavier demands on their health systems than normal in recent years for seasonal influenza[20]. In the graph above UK data is additively displayed, but in graph below UK data is shown non-additively to illustrate the problems with suspected cases and publicity bias. WHO stopped consistent daily updates on 30/5/09 and ECDC figures were increasingly used after this date. The ECDC has analysed the early European data by date of onset and there are two distinct phases, the first associated with travelers returning from Mexico peaking about 27th April and almost disappearing in second week of May. The second was associated with travel to the USA which really started in 3rd week of May, and these imported cases peaked in the first few days of June and then internal secondary transmission cases became more dominant.

The plots below show time course from 1st March 2009 to 1st June 2009

The data below shows incident data from Mexico first wave. At the peak of the outbreak, about 27th April there were about 1300 new probable cases a day, never confirmed or excluded known to the authorities and an additional 385 confirmed cases as shown occurred that day (data up to 2nd June, will increase slightly as later tests come in). The data displayed in the last few days of May is definitely incomplete and likely to increase from 2 cases to over ten/day.

Later time course

The northern hemisphere influenza season began early by about ten weeks with by the first week of November activity in many countries above baseline with marked predominance of influenza A(H1N1)v from isolates in almost all countries (Kenya was an exception). Mexico had more cases during September than during its first wave. The second wave in the USA had by the end of October produced more cases of acute respiratory illnesses than any of the six previous influenza seasons. The most spectacular early winter epidemic outbreak was in the Ukraine where in the first week of November the deaths tripled and hospitalisation's for respiratory illness increased 20 fold from less than a thousand to over 20,000.

Prevention

Antivirals

Whether and in whom antivirals should be used has been - at least in part - a matter of some controversy.

The UK government was initially keen that everybody with swine flu should be identified and offered antivirals. Others are of the view that only those in high risk groups should be offered the vaccine. (Lots of refs now, including one from WHO, and these two.[21][22]) As time has passed, a more considered review commissioned by government (the Hine report) has largely supported the approach taken, calling it "highly satisfactory",[23] while at least one other paper has criticised the response taken, and the Hine report for failing to consult appropriately.[24]

Arguments in favour of widespread use of antivirals include:

  • Some of the patients who have been seriously ill or died were not in risk groups.
  • Voter backlash if people who are seriously ill or died had been "denied" antivirals.

Arguments against widespread use of antivirals include:

  • Systems have struggled to provide antivirals in time for them to be effective; and attempting to provide them to people outside risk groups may delay their provision to people in risk groups, who are more likely to benefit.
  • The likelihood that this will drive the selection of strains of virus which are resistant to antivirals.

Vaccination

See 2009 Swine flu vaccine. Vaccine supplies began to be available from about October.

Other information

Terminology

Officially renamed on 30 April 2009 influenza A(H1N1) by WHO[25] and later influenza A(H1N1)v[1] to make things fairer for Sus spp. who have plenty of flu that does not transmit between homo sapiens. The pandemic will forever be referred to as Swine flu but is officially termed influenza (pandemic (H1N1) 2009) (WHO) or influenza pandemic (H1N1) 2009 (ECDC)

Why Swine not pig or porcine? An interesting comment from the International Society for Infectious Diseases sheds some light on the inadequacies of terminology [26]. The first (index) isolate is called A/California/04/2009. It is a quadruple recombinant of two swine influenza, an avian influenza and a human influenza virus subtype. With genetic drift etc there are now several well characterised isolates world wide and more might be expected if a pandemic eventuates.

WHO Influenza Pandemic Phases

see Influenza phases

Transmission on aircraft

This is certainly possible although the risks are lower than with house hold contacts, as shown by analysis of a cluster of exposure from an infected group of high school students on a jumbo jet[27]. However analysis by seating plan suggests some cases might have been spread by surface contamination. It is known that good hand hygiene reduces rates of influenza transmission. The problems in achieving adequate public health follow up when the situation is only realised a few hours after the aircraft has landed were particularly severe in transit and non resident international air passengers.

Ganfyd pages

Early "quick and dirty" analysis

  • First formal hospitalization rate data from USA outbreak indicates 9% rate with 36% of these needing ITU[8]
  • The WHO Rapid Pandemic Assessment Collaboration published on 11th May 2009 an early on line analysis [28].

They estimated that by late April there were 23,000 cases in Mexico giving a case fatality ratio (CFR) of 0.4%. This appears less than 1918 Spanish Flu but more than 1957. Transmissability seems higher than seasonal flu. The Collaboration emphasises that these are very early and rough figures. Later data from Japan suggested the CFR might be as low as 0.1%.

  • Planning assumptions for the European first wave based mainly on UK data have been published[29]

Fitness to return to work after swine flu

It is thought that children can shed the virus for up to 7 days after the onset of symptoms, and adults for up to 5 days.

If a patient works with particularly vulnerable people and still has mild symptoms after 7 days, it may be wise to exclude them for a little longer - until symptoms cease, or until 10 days from the onset of symptoms, whichever is the shorter. (Of course, if they have more serious symptoms they are unlikely to be fit for work anyhow).

Flag of the United Kingdom.png

GPs are not required to provide "fitness to work" certificates for employers who are concerned that patients may be an infection risk, having had [possible] swine flu. This is the responsibility of the employer's occupational health service. If GPs are asked to provide this service they may charge a fee. Before providing such information GPs may require employers to agree to pay for the service, and to seek signed consent from the patient, possibly along the lines of the GANFYD general note.

Later more informed analysis

  • A pandemic did occur of mild to moderate significance.
  • Maximium first wave influenzae like illness consultation rates in the UK varied from about 250/100000 in Northern Ireland to no more than 50/100000 in Scotland.
  • There is still potential for a simple single mutation to transform this virus into one with high lethal potential in further waves[10].

Protection implications of being infected

There is some evidence that survivors can develop neutralizing antibodies broadly reactive against other H1N1 and H5N1 influenza strains [30]. However this was over-hyped in the media as a potential universal benefit which is not the case as some strains of influenza were not protected against such as H3N2 and the main implication is that antibodies directed to different parts of the haemagglutinin protein than at present may offer a better vaccination spectrum.

Key web sites

Further (more detailed and current) information is/will be available at the following web sites:

External links

References

  1. a b ProMED-Mail. Influenza A (H1N1) - worldwide (86): official nomenclature. 2009; Updated 6 July 2009; Accessed: 2009 (31 July)
  2. ECDC Seasonal influenza update 15 December 2010
  3. a b World Health Organization. Pandemic (H1N1) 2009—update 112. 2010
  4. a b Offical WHO statement of end of pandemic
  5. a b SALUD Situación actual de la epidemia 22 May 2009
  6. ECDC situation report 14 May 2009
  7. Presanis AM, Pebody RG, Paterson BJ, Tom BD, Birrell PJ, Charlett A, Lipsitch M, Angelis DD. Changes in severity of 2009 pandemic A/H1N1 influenza in England: a Bayesian evidence synthesis. BMJ (Clinical research ed.). 2011; 343:d5408.(Epub)
  8. a b c d e http://content.nejm.org/cgi/content/full/NEJMoa0903810 Emergence of a Novel Swine-Origin Influenza A (H1N1) Virus in Humans NEJM 10.1056/NEJMoa0903810 accessed 7 May 2009
  9. HPA Weekly update Week 38
  10. a b Kilander A, Rykkvin R, Dudman SG, Hungnes O. Observed association between the HA1 mutation D222G in the 2009 pandemic influenza A(H1N1) virus and severe clinical outcome, Norway 2009-2010 Euro Surveill. 2010;15(9):pii=19498
  11. Rasmussen SA, Jamieson DJ. 2009 H1N1 Influenza and Pregnancy - 5 Years Later. The New England journal of medicine. 2014 Oct 9; 371(15):1373-1375.(Link to article – subscription may be required.)
  12. Intensive-Care Patients With Severe Novel Influenza A (H1N1) Virus Infection - Michigan, June 2009 CDC MMWR 10 July 2009
  13. ECDC Interim Risk Assessment - Influenza A(H1N1) 2009 pandemic 20 July 2009
  14. WHO PANDEMIC ALERT PHASE 5: Algorithm for the management of returning travellers and visitors from countries affected by swine influenza A/H1N1 presenting with febrile respiratory illness: recognition, investigation and initial management. Udated on 12 May 2009. Last viewed pm 14 May 2009. Please check HPA web site for updates - this file has been updated every few days since 25 April, but apparently using the same URL.)
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