Pandemic (H1N1) 2009 briefing note 10

    11 SEPTEMBER 2009 | GENEVA -- WHO is today issuing advice on measures that can be undertaken in schools to reduce the impact of the H1N1 influenza pandemic. Recommendations draw on recent experiences in several countries as well as studies of the health, economic, and social consequences of school closures. These studies were undertaken by members of a WHO informal network for mathematical modelling of the pandemic.

     Experience to date has demonstrated the role of schools in amplifying transmission of the pandemic virus, both within schools and into the wider community. While outbreaks in schools are clearly an important dimension of the current pandemic, no single measure can stop or limit transmission in schools, which provide multiple opportunities for spread of the virus.

     WHO recommends the use of a range of measures that can be adapted to the local epidemiological situation, available resources, and the social role played by many schools. National and local authorities are in the best position to make decisions about these measures and how they should be adapted and implemented.

     WHO continues to recommend that students, teachers, and other staff who feel unwell should stay home. Plans should be in place, and space made available, to isolate students and staff who become ill while at school.
Schools should promote hand hygiene and respiratory etiquette and be stocked with appropriate supplies. Proper cleaning and ventilation and measures to reduce crowding are also advised.

School closures and class suspensions

    Decisions about if and when schools should be closed during the pandemic are complex and highly context-specific. WHO cannot provide specific recommendations for or against school closure that are applicable to all settings. However, some general guidance comes from recent experience in several countries in both the northern and southern hemispheres, mathematical modelling, and experience during seasonal epidemics of influenza.

    School closure can operate as a proactive measure, aimed at reducing transmission in the school and spread into the wider community. School closure can also be a reactive measure, when schools close or classes are suspended because high levels of absenteeism among students and staff make it impractical to continue classes.

     The main health benefit of proactive school closure comes from slowing down the spread of an outbreak within a given area and thus flattening the peak of infections. This benefit becomes especially important when the number of people requiring medical care at the peak of the pandemic threatens to saturate or overwhelm health care capacity. By slowing the speed of spread, school closure can also buy some time as countries intensify preparedness measures or build up supplies of vaccines, antiviral drugs, and other interventions.

    The timing of school closure is critically important. Modelling studies suggest that school closure has its greatest benefits when schools are closed very early in an outbreak, ideally before 1% of the population falls ill. Under ideal conditions, school closure can reduce the demand for health care by an estimated 30–50% at the peak of the pandemic. However, if schools close too late in the course of a community-wide outbreak, the resulting reduction in transmission is likely to be very limited.

    Policies for school closure need to include measures that limit contact among students when not in school. If students congregate in a setting other than a school, they will continue to spread the virus, and the benefits of school closure will be greatly reduced, if not negated.

Economic and social costs

    When making decisions, health officials and school authorities need to be aware of economic and social costs that can be disproportionately high when viewed against these potential benefits.

    The main economic cost arises from absenteeism of working parents or guardians who have to stay home to take care of their children. Studies estimate that school closures can lead to the absence of 16% of the workforce, in addition to normal levels of absenteeism and absenteeism due to illness. Such estimates will, however, vary considerably across countries depending on several factors, including the structure of the workforce.

    Paradoxically, while school closure can reduce the peak demand on health care systems, it can also disrupt the provision of essential health care, as many doctors and nurses are parents of school-age children.

    Decisions also need to consider social welfare issues. Children’s health and well-being can be compromised if highly beneficial school-based social programmes, such as the provision of meals, are interrupted or if young children are left at home without supervision.

Weekly update

In the temperate region of the southern hemisphere (represented by countries such as Chile, Argentina, Australia, New Zealand, and South Africa), influenza activity continues to decrease or return to baseline.

Active transmission persists in tropical regions of the Americas and Asia. Many countries in Central America and the Caribbean continue to report declining activity for the second week in a row. However, countries in the tropical region of South America (represented by countries such as Bolivia, Ecuador, and Venezuela) are reporting increasing levels of respiratory disease. In the tropical regions of Asia, respiratory disease activity remains geographically regional or widespread but the trend is generally increasing as noted in India, Bangladesh, and Cambodia.

In the temperate regions of the Northern Hemisphere activity is variable. In the United States, regional increases in influenza activity are being reported, most notably in the south eastern states. Most of Europe is reporting low or moderate respiratory diseases activity, but parts of Eastern Europe are beginning to report increases in activity.

WHO Collaborating Centres and other laboratories continue to report sporadic isolates of oseltamivir resistant influenza virus. 21 such virus isolates have now been described from around the world, all of which carry the same H275Y mutation that confers resistance to the antiviral oseltamivir but not to the antiviral zanamivir. Of these, 12 have been associated with post-exposure prophylaxis, four with long term oseltamivir treatment in patients with immunosuppression. Worldwide, over 10,000 isolates of the pandemic (H1N1) 2009 virus have been tested and found to be sensitive to oseltamivir. WHO will continue to monitor the situation closely in collaboration with its partners, but is not changing its guidelines for use of antiviral drugs at this time.

Pandemic (H1N1) influenza virus continues to be the predominant circulating virus of influenza, both in the northern and southern hemisphere. All pandemic H1N1 2009 influenza viruses analysed to date have been antigenically and genetically similar to A/California/7/2009-like pandemic H1N1 2009 virus. See below for detailed laboratory surveillance update.

Of note, the U.S. Centers for Disease Control and Prevention this week reported on an analysis of 36 fatal pandemic influenza cases in children under the age of 18 years. Sixty-eight percent of the children had one or more high-risk medical conditions, most commonly neurodevelopmental disorders. In addition, ten of 23 children for whom data were available were found to have strong evidence of secondary bacterial co-infections.
Weekly update (Virological surveillance data)

Qualitative indicators (Week 29 to Week 35: 13 July - 30 August 2009)

The qualitative indicators monitor: the global geographic spread of influenza, trends in acute respiratory diseases, the intensity of respiratory disease activity, and the impact of the pandemic on health-care services.
Human infection with pandemic (H1N1) 2009 virus: updated interim WHO guidance on global surveillance
A description of WHO pandemic monitoring and surveillance objectives and methods can be found in the updated interim WHO guidance for the surveillance of human infection with pandemic (H1N1) virus.
The maps below display information on the qualitative indicators reported during weeks 29 to 34. Information is available for approximately 60 countries each week. Implementation of this monitoring system is ongoing and completeness of reporting is expected to increase over time.
List of definitions of qualitative indicators

Geographic spread of influenza activity

Map timeline

Trend of respiratory diseases activity compared to the previous week

Map timeline

Intensity of acute respiratory diseases in the population

Map timeline

Impact on health care services

Map timeline

Laboratory-confirmed cases of pandemic (H1N1) 2009 as officially reported to WHO by States Parties to the IHR (2005) as of 6 September 2009

Map of affected countries and deaths as of 6 September 2009

*Given that countries are no longer required to test and report individual cases, the number of cases reported actually understates the real number of cases.

    Relevé épidémiologique hebdomadaire 4 septembre 2009, 84e année

Updated 11 June 2009
What is phase 6?
Phase 6 is a pandemic, according to the WHO definition.
WHO pandemic phase descriptions [pdf 456kb]

Pandemic influenza preparedness and response
What about severity?
At this time, WHO considers the overall severity of the influenza pandemic to be moderate. This assessment is based on scientific evidence available to WHO, as well as input from its Member States on the pandemic's impact on their health systems, and their social and economic functioning.
The moderate assessment reflects that:

• Most people recover from infection without the need for hospitalization or medical care.
• Overall, national levels of severe illness from influenza A(H1N1) appear similar to levels seen during local seasonal influenza periods, although high levels of disease have occurred in some local areas and institutions.
• Overall, hospitals and health care systems in most countries have been able to cope with the numbers of people seeking care, although some facilities and systems have been stressed in some localities.

WHO is concerned about current patterns of serious cases and deaths that are occurring primarily among young persons, including the previously healthy and those with pre-existing medical conditions or pregnancy.
Large outbreaks of disease have not yet been reported in many countries, and the full clinical spectrum of disease is not yet known.
Assessing the severity of an influenza pandemic

Considerations for assessing the severity [pdf 318kb]
Does WHO expect the severity of the pandemic to change over time?
The severity of pandemics can change over time and differ by location or population.
Close monitoring of the disease and timely and regular sharing of information between WHO and its Member States during the pandemic period is essential to determine future severity assessments, if needed.
Future severity assessments would reflect one or a combination of the following factors:

• changes in the virus,
• underlying vulnerabilities, or
• limitations in health system capacities.

The pandemic is early in its evolution and many countries have not yet been substantially affected.

   25 May 2009 -- As of 06:00 GMT, 25 May 2009, 46 countries have officially reported 12 515 cases of influenza A(H1N1) infection, including 91 deaths.
The breakdown of the number of laboratory-confirmed cases by country is given in the following table and map.

   Laboratory-confirmed cases of new influenza A(H1N1) as officially reported to WHO by States Parties to the International Health Regulations (2005)

Chinese Taipei has reported 1 confirmed case of influenza A (H1N1) with 0 deaths. Cases from Chinese Taipei are included in the cumulative totals provided in the table above.

Cumulative and new figures are subject to revision

   17 May 2009 -- As of 06:00 GMT, 17 May 2009, 39 countries have officially reported 8480 cases of influenza A(H1N1) infection.

   Mexico has reported 2895 laboratory confirmed human cases of infection, including 66 deaths. The United States has reported 4714 laboratory confirmed human cases, including four deaths. Canada has reported 496 laboratory confirmed human cases, including one death. Costa Rica has reported nine laboratory confirmed human cases, including one death.

   The following countries have reported laboratory confirmed cases with no deaths - Argentina (1), Australia (1), Austria (1), Belgium (4), Brazil (8), China (5), Colombia (11), Cuba (3), Denmark (1), Ecuador (1), El Salvador (4), Finland (2), France (14), Germany (14), Guatemala (3), India (1), Ireland (1), Israel (7), Italy (9), Japan (7), Malaysia (2), Netherlands (3), New Zealand (9), Norway (2), Panama (54), Peru (1), Poland (1), Portugal (1), Republic of Korea (3), Spain (103), Sweden (3), Switzerland (1), Thailand (2), Turkey (1), and the United Kingdom (82).

   WHO is not recommending travel restrictions related to the outbreak of the influenza A(H1N1) virus.

   Individuals who are ill should delay travel plans and returning travelers who fall ill should seek appropriate medical care. These recommendations are prudent measures which can limit the spread of many communicable diseases, including influenza.

   Further information on the situation will be available on the WHO web site on a regular basis

   15 May 2009 -- As of 06:00 GMT, 15 May 2009, 34 countries have officially reported 7520 cases of influenza A(H1N1) infection.

   Mexico has reported 2446 laboratory confirmed human cases of infection, including 60 deaths. The United States has reported 4298 laboratory confirmed human cases, including three deaths. Canada has reported 449 laboratory confirmed human cases, including one death. Costa Rica has reported eight laboratory confirmed human cases, including one death.

   The following countries have reported laboratory confirmed cases with no deaths - Argentina (1), Australia (1), Austria (1), Belgium (1), Brazil (8), China (4), Colombia (10), Cuba (3), Denmark (1), El Salvador (4), Finland (2), France (14), Germany (12), Guatemala (3), Ireland (1), Israel (7), Italy (9), Japan (4), Netherlands (3), New Zealand (7), Norway (2), Panama (40), Poland (1), Portugal (1), Republic of Korea (3), Spain (100), Sweden (2), Switzerland (1), Thailand (2), and the United Kingdom (71).

   WHO is not recommending travel restrictions related to the outbreak of the influenza A(H1N1) virus.

   Individuals who are ill should delay travel plans and returning travelers who fall ill should seek appropriate medical care. These recommendations are prudent measures which can limit the spread of many communicable diseases, including influenza.

   Further information on the situation will be available on the WHO web site on a regular basis.

Current phase of alert in the WHO global influenza preparedness plan

   In the 2009 revision of the phase descriptions, WHO has retained the use of a six-phased approach for easy incorporation of new recommendations and approaches into existing national preparedness and response plans. The grouping and description of pandemic phases have been revised to make them easier to understand, more precise, and based upon observable phenomena.
    Phases 1–3 correlate with preparedness, including capacity development and response planning activities, while Phases 4–6 clearly signal the need for response and mitigation efforts. Furthermore, periods after the first pandemic wave are elaborated to facilitate post pandemic recovery activities.
.
The current WHO phase of pandemic alert is 3.

   In nature, influenza viruses circulate continuously among animals, especially birds. Even though such viruses might theoretically develop into pandemic viruses, in Phase 1 no viruses circulating among animals have been reported to cause infections in humans.

   In Phase 2 an animal influenza virus circulating among domesticated or wild animals is known to have caused infection in humans, and is therefore considered a potential pandemic threat.

   In Phase 3, an animal or human-animal influenza reassortant virus has caused sporadic cases or small clusters of disease in people, but has not resulted in human-to-human transmission sufficient to sustain community-level outbreaks. Limited human-to-human transmission may occur under some circumstances, for example, when there is close contact between an infected person and an unprotected caregiver. However, limited transmission under such restricted circumstances does not indicate that the virus has gained the level of transmissibility among humans necessary to cause a pandemic.

   Phase 4 is characterized by verified human-to-human transmission of an animal or human-animal influenza reassortant virus able to cause “community-level outbreaks.” The ability to cause sustained disease outbreaks in a community marks a significant upwards shift in the risk for a pandemic. Any country that suspects or has verified such an event should urgently consult with WHO so that the situation can be jointly assessed and a decision made by the affected country if implementation of a rapid pandemic containment operation is warranted. Phase 4 indicates a significant increase in risk of a pandemic but does not necessarily mean that a pandemic is a forgone conclusion.

   Phase 5 is characterized by human-to-human spread of the virus into at least two countries in one WHO region (Figure 4). While most countries will not be affected at this stage, the declaration of Phase 5 is a strong signal that a pandemic is imminent and that the time to finalize the organization, communication, and implementation of the planned mitigation measures is short.

   Phase 6, the pandemic phase, is characterized by community level outbreaks in at least one other country in a different WHO region in addition to the criteria defined in Phase 5. Designation of this phase will indicate that a global pandemic is under way.
During the post-peak period, pandemic disease levels in most countries with adequate surveillance will have dropped below peak observed levels. The post-peak period signifies that pandemic activity appears to be decreasing; however, it is uncertain if additional waves will occur and countries will need to be prepared for a second wave.
Previous pandemics have been characterized by waves of activity spread over months. Once the level of disease activity drops, a critical communications task will be to balance this information with the possibility of another wave. Pandemic waves can be separated by months and an immediate “at-ease” signal may be premature.

   In the post-pandemic period, influenza disease activity will have returned to levels normally seen for seasonal influenza. It is expected that the pandemic virus will behave as a seasonal influenza A virus. At this stage, it is important to maintain surveillance and update pandemic preparedness and response plans accordingly. An intensive phase of recovery and evaluation may be required.

   26 April 2009 -- As of 26 April 2009, the United States Government has reported 20 laboratory confirmed human cases of swine influenza A/H1N1 (8 in New York, 7 in California, 2 in Texas, 2 in Kansas and 1 in Ohio). All 20 cases have had mild Influenza-Like Illness with only one requiring brief hospitalization. No deaths have been reported. All 20 viruses have the same genetic pattern based on preliminary testing. The virus is being described as a new subtype of A/H1N1 not previously detected in swine or humans.

   Also as of 26 April, the Government of Mexico has reported 18 laboratory confirmed cases of swine influenza A/H1N1. Investigation is continuing to clarify the spread and severity of the disease in Mexico. Suspect clinical cases have been reported in 19 of the country's 32 states.

   WHO and the Global Alert and Response Network (GOARN) are sending experts to Mexico to work with health authorities. WHO and its partners are actively investigating reports of suspect cases in other Member States as they occur, and are supporting field epidemiology activities, laboratory diagnosis and clinical management.

   On Saturday, 25 April, upon the advice of the Emergency Committee called under the rules of the International Health Regulations, the Director-General declared this event a Public Health Emergency of International Concern.

WHO is not recommending any travel or trade restrictions

RÉPARTITION MONDIALE DES ÉTABLISSEMENTS ET DES RÉSEAUX PARTENAIRES DE GOARN
   Aucune institution ni aucun pays n'a seul toutes les capacités pour répondre à une urgence de santé publique qu'elle soit due à une épidémie ou à une maladie émergente. Cette carte montre la répartition des différents établissements associés de GOARN et des réseaux partenaires dans le monde. Là où plus d'un partenaire du réseau est répertorié, le nombre est indiqué dans les boîtes à textes. Les appellations employées dans la présente publication et la présentation des données qui y figurent n’impliquent de la part de l’Organisation mondiale de la Santé aucune prise de position quant au statut juridique des pays, territoires, villes ou zones, ou de leurs autorités, ni quant au tracé de leurs frontières ou limites. Les lignes en pointillé sur les cartes représentent des frontières approximatives dont le tracé peut ne pas avoir fait l'objet d'un accord définitif.

Source des données: WHO/GOARN
Production cartographique: Groupe de cartographie de la santé publique & SIG
Maladies Transmissibles (CDS)
Organisation Mondiale de la Santé
©OMS 2005. Tous droits réservés