#5614
Although relatively mild by pandemic standards, the novel H1N1 virus of 2009 will undoubtedly turn out to be the most studied influenza outbreak in history. Two years after the outbreak began, we continue to see new and sometimes surprising research being published.
Today, we’ve a seroprevalence study appearing in PLoS One that looks at the incidence of infection by the 2009 H1N1 pandemic virus in eastern Scotland during the pandemic.
It finds that transmission rates, and number of people infected, was far higher than previously believed; more than 40% of adults tested showed specific antibodies to the pandemic flu.
A snippet from the open access study follows, after which I’ll return with more.
Sero-Prevalence and Incidence of A/H1N1 2009 Influenza Infection in Scotland in Winter 2009–2010
Nigel J. McLeish, Peter Simmonds, Chris Robertson, Ian Handel, Mark McGilchrist, Brajendra K. Singh, Shona Kerr, Margo E. Chase-Topping, Katy Sinka, Mark Bronsvoort, David J. Porteous, William Carman, James McMenamin, Andrew Leigh-Brown, Mark E. J. Woolhouse
(EXCERPTS)
Methods and Findings
We obtained serum samples from a representative sample of 1563 adults resident in Scotland between late October 2009 and April 2010.
Based on a microneutralisation assay, we estimate that 44% (95% confidence intervals (CIs): 40–47%) of the adult population of Scotland were sero-positive for A/H1N1 2009 influenza by 1 March 2010.
Correcting for background cross-reactivity and for recorded vaccination rates by time and age group, we estimated that 34% (27–42%) were naturally infected with A/H1N1 2009 by 1 March 2010.
The central estimate increases to >40% if we allow for imperfect test sensitivity.
<SNIP>
Conclusions
We estimate that almost half the adult population of Scotland were sero-positive for A/H1N1 2009 influenza by early 2010 and that the majority of these individuals (except in the oldest age classes) sero-converted as a result of natural infection with A/H1N1 2009. Public health planning should consider the possibility of higher rates of infection with A/H1N1 2009 influenza in more deprived areas.
There is also a press release from the University of Edinburgh, which led this study.
Swine flu spread was much wider than first thought, scientists say
The swine flu outbreak of winter 2009-2010 was much more widespread than was previously realized, research suggests
The swine flu outbreak of winter 2009-2010 was much more widespread than was previously realised, research suggests.
Blood samples taken from Scottish adults in March last year at the end of the H1N1 flu season showed that almost half were carrying antibodies to the virus.
Most of the 44 per cent who tested positive had contracted swine flu, although some had acquired immunity from a previous bout of flu, or had been vaccinated.
The research, led by the University of Edinburgh, shows that many cases of swine flu went unreported. Only 100,000 people consulted their GP regarding flu, out of about two million who are believed to have contracted the virus.
People living in the most deprived areas were twice as likely to have contracted the virus. Scientists add that it is possible that many people who were vaccinated against the virus were already immune.
What makes this research particularly interesting is that the attack rate of the H1N1 virus in this study appears to be higher than earlier studies would have suggested.
Last summer, in New Zealand Seroprevalence Study On H1N1, researchers came up with a much lower attack rate (approx. 20%, half asymptomatic).
And in late 2009, in UK: H1N1 Serology Tests Reveal Significant Asymptomatic Rate a small study revealed that about 1/3rd of children tested – who were believed more susceptible to the virus than adults – showed antibodies to the virus, while only about 1 in 10 reported flu symptoms.
While we were lucky that this virus produced mild (or even asymptomatic) illness in most cases, the next novel virus to erupt may not be nearly so accommodating.
So research such as this is of more than just academic interest.
It helps to increase our understanding of the attack rates and the patterns of community spread of a novel influenza virus, which should help planners better prepare for the next pandemic.
