The Influenza A H1N1 pandemic (A H1N1) occurred between June 2009 and August 2010. Although the pandemic is now over, the virus has emerged as the predominant strain in the current seasonal influenza phase in the northern hemisphere. The A H1N1 influenza is a novel strain of the influenza A virus and is widely known as swine flu. The virus contains a mixture of genetic material from human, pig and bird flu virus. It is a new variety of flu which people have not had much immunity to. Much has been learnt from the Pandemic of 2009/2010 but the messages about vaccination and treatment seem to be taken slowly by the clinical profession. Most people affected by the virus, including pregnant women, suffer a mild viral illness, and make a full recovery. The median duration of illness is around seven days. This influenza typically affects the younger age group i.e. from the ages of 5–65 years. Current experience shows that the age group experiencing increased morbidity and mortality rates are in those under 65 years of age. Pregnant women, because of their altered immunity and physiological adaptations, are at higher risk of developing pulmonary complications, especially in the second and third trimesters. In the United Kingdom, twelve maternal deaths were reported to be associated with the H1N1 virus during the pandemic and clear avoidable factors were identified (Modder, Review of Maternal Deaths in the UK related to A H1N1 2009 influenza (CMACE). www.cmace.org.uk, 2010). The pregnancy outcomes were also poor for women who were affected by the virus with a fivefold increase in the perinatal mortality rate and threefold increase in the preterm delivery rate (Yates et al. Health Technol Assess 14(34):109–182, 2010). There continues to be a low uptake of the flu vaccine and commencement of antiviral treatment for pregnant women.
Keywords : A H1N1 influenza , Swine flu , Pregnancy , Antiviral drugs , Vaccines
Although the outbreak of influenza A H1N1 2009 appeared first in Mexico in April 2009, this was followed by a growing number of cases reported across the globe. The outbreak of the novel A H1N1 virus (swine flu) was declared a global pandemic by the World Health Organisation (WHO) from 11 June 2009 until 10 August 2010. These pandemics happen when a new influenza virus, to which the population has little or no immunity emerges and starts to spread. Unlike seasonal influenza, high rates of disease due to a pandemic virus may occur throughout the year. Swine flu is a novel strain of the influenza A virus affecting humans and contains segments of genes from pig, bird and human influenza viruses.
The WHO classifies the spread of infections such as influenza in terms of phases. Phase 6 or a global pandemic is declared when the infection is characterized by humanto-human spread of the virus with community level outbreaks in at least two WHO regions, meaning that there is widespread global transmission.
The influenza A virus has been responsible for three global pandemics in the last century: the Spanish Flu in 1918, Asian Flu in 1957 and the Hong Kong Flu in 1968. These pandemics were responsible for a large number of fatalities, the Spanish Flu being the most severe and caused severe pneumonias, particularly among pregnant women (Table 1). A recently published epidemiological study about cohorts born in and around the pandemic estimated that the individuals born had a[20% excess cardiovascular disease at 60–82 years of age, relative to those born without exposure to the influenza epidemic, thus suggesting that prenatal exposure to even uncomplicated maternal influenza may have lasting consequences later in life [3]
The 1918 pandemic was associated with a high maternal mortality rate of 27% and also associated with high rates of spontaneous miscarriage and preterm labour. In the 1957 pandemic, a 20% maternal mortality rate was reported and increased incidences of birth defects such as neural tube defects and cardiac abnormalities were reported.
Although we are now in the post pandemic phase, the A
H1N1 virus has now emerged as the predominant strain of
virus in the seasonal influenza season that is currently
affecting the northern hemisphere. Current experience in
the United Kingdom shows that the population below the
age of 65 years are worst affected by the complications of
the flu and that the deaths associated with the flu are predominantly associated with the H1N1 virus. From
October 2010 to early January 2011, 50 deaths were
reported by the Health Protection Agency. Forty-five of
these people died with the H1N1 (2009) strain and 5 with
Influenza B. The majority were under 65 years of age and
five were under the age of five [4].
