The World Health Organization (WHO) recommends the strains to be included in each season’s influenza vaccine. The WHO yesterday (2/18/10) recommended that the pandemic H1N1 strain that caused epidemics in the United States in April and October be included in the 2010/2011 influenza vaccine. The official name of the virus is A/California/7/2009 (H1N1). Influenza viruses are named by the type (A), the location where the strain was first officially identified (California, even though we suspect it originated in Mexico), and the year. This is the same strain that was in the H1N1 vaccine this year.
Because this strain will now be included in all the standard influenza vaccines next season, we will not need a second vaccine for this strain. One vaccine should be all we need, unless some new strain emerges again. It is a challenge to get people immunized each year with one vaccine, and having to give two vaccines to prevent influenza in 2009 was clearly a barrier to protecting the public. One dose will be much easier.
Although the 2009 H1N1 influenza epidemic was severe in certain populations and caused many deaths, the good news is that the vaccine made for it has been very safe and effective, and the virus remains susceptible to our antiviral drugs we use to treat it.