Emergencies preparedness, response

WHO recommendations for the post-pandemic period

Pandemic (H1N1) 2009 briefing note 23

The world is now in the post-pandemic period. Based on knowledge about past pandemics, the H1N1 (2009) virus is expected to continue to circulate as a seasonal virus for some years to come. While the level of concern is now greatly diminished, vigilance on the part of national health authorities remains important. Such vigilance is especially critical in the immediate post-pandemic period, when the behaviour of the H1N1 (2009) virus as a seasonal virus cannot be reliably predicted.

For example, it is likely that the virus will continue to disproportionately affect a younger age group, at least in the immediate post-pandemic period. Groups identified during the pandemic as at higher risk of severe or fatal illness will probably remain at heightened risk, though the number of such cases could diminish. In addition, a small proportion of people infected during the pandemic developed a severe form of primary viral pneumonia that is not commonly seen during seasonal epidemics and is especially difficult to treat. It is not known whether this pattern will continue during the post-pandemic period, further emphasizing the need for vigilance.

WHO is today issuing guidance on recommended activities during the post-pandemic period, including advice on epidemiological and virological monitoring, vaccination, and the clinical management of cases.

National health authorities are reminded that cases and local outbreaks of H1N1 (2009) infection will continue to occur, and in some locations, such outbreaks could have a substantial impact on communities.

WHO recommendations to health authorities during the post-pandemic period

Monitoring of respiratory disease activity

WHO recommends that surveillance during the post-pandemic period include:

  • monitoring for unusual events, such as clusters of severe respiratory illness or death;
  • investigating severe or unusual cases, clusters or outbreaks to facilitate rapid identification of important changes in the epidemiology or severity of influenza;
  • maintaining routine surveillance, including for influenza-like illness and cases of severe acute respiratory infections;
  • continuing to use routine channels of data transmission, such as FluID, FluNet, and EUROFlu, to transmit data from the routine surveillance of respiratory disease;
  • notifying WHO (including, where appropriate, notifications under the International Health Regulations) immediately if any of the following changes are detected:
    • sustained transmission of antiviral-resistant H1N1 2009 influenza
    • human cases of infection with any influenza virus not currently circulating in human populations
    • any notable changes in the severity or other epidemiological or clinical characteristics of the H1N1 2009 virus, including changes in the age distribution, the clinical appearance, proportion of cases requiring intensive management, or unexpected increases in numbers of cases.
  • monitoring the H1N1 2009 virus for important genetic, antigenic or functional changes, such as antiviral drug sensitivity.

Vaccination remains important as a means of reducing the morbidity and mortality caused by influenza viruses. WHO strongly recommends vaccination of high-risk individuals in countries where influenza vaccines are available.

The H1N1 influenza virus, which caused the 2009 pandemic, continues to circulate in some parts of the world, causing variable levels of disease and outbreaks. In some countries, seasonal[1] trivalent vaccines are available that cover the H1N1 (2009) virus. In other countries, however, seasonal influenza vaccines are not available. WHO advises that there is still public health value in using monovalent H1N1 vaccine (where available) to immunize persons at risk of severe disease from H1N1 influenza infection, especially where trivalent seasonal influenza vaccine is not available.

Such monovalent H1N1 influenza vaccines should be used according to guidelines of National Regulatory Authorities. WHO will continue to seek advice from the Strategic Advisory Group of Experts (SAGE) as the situation evolves.

Clinical management

Persons suspected of illness from influenza should receive appropriate clinical care. WHO’s guidelines for clinical management, which refer to both seasonal and pandemic influenza, offer guidance. The H1N1 (2009) virus is expected to continue to circulate as a seasonal virus for some years to come. Cases of severe illness in higher-risk individuals, as well as in otherwise healthy individuals, are likely to occur. Early recognition and appropriate treatment of such cases remains important. WHO’s guidelines for use of antiviral medicines, which refer to both seasonal and pandemic influenza, should continue to be followed.

Groups at increased risk of severe illness from the pandemic H1N1 virus included young children, pregnant women, and people with underlying respiratory or other chronic conditions, including asthma and diabetes. Patients who have severe or deteriorating influenza should be treated as soon as possible with oseltamivir. Patients who are at higher risk of severe or complicated influenza should be treated with oseltamivir or zanamivir as soon as possible.

Related links

[1]WHO has recommended that the H1N1 (2009) influenza strain be included in both 2010 southern hemisphere and 2010-11 northern hemisphere trivalent seasonal influenza vaccines.