As announced on 10 August, the world is now in the post-pandemic period. Based on knowledge about past pandemics, the H1N1 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 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 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 the following activities:
- Monitoring for unusual events, such as clusters of severe respiratory illness or death.
- Investigation of severe or unusual cases, clusters or outbreaks to facilitate the rapid identification of important changes in the epidemiology or severity of influenza.
- Maintain routine surveillance, including for influenza-like illness and cases of severe acute respiratory infections.
Continue to use routine channels of data transmission, such as FluID, FluNet, and EUROFlu, to transmit data from the routine surveillance of respiratory disease.
- Notify 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.
- Monitor 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.
Protection against the H1N1 2009 virus can be conferred through either the monovalent (single virus) pandemic H1N1 2009 vaccines or the current trivalent seasonal influenza vaccines. The trivalent seasonal vaccines now contain the H1N1 2009 virus, which replaces the pre-pandemic H1 strain that is no longer circulating, as well as H3 and B circulating seasonal influenza strains.
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 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.