WHO recommendations for influenza virus vaccine 2002/03

The new subtype of the influenza A virus, A(H1N2), is a combination of components present in the strains of the two influenza A subtypes (H1N1 and H3N2) currently contained in the vaccine, and so people who have received the vaccine should have a good level of immunity to the new subtype. People in the general population who have not been vaccinated should also have some immunity due to the circulation of the H1N1 and H3N2 subtypes over the last two decades.