Alternate vaccine strain selection in the wake of emerging foot-and-mouth disease virus serotype A antigenic variants in India

‘National foot-and-mouth disease (FMD) control programme’ is being implemented in India and therefore predicting vaccine match is a key surveillance task. Recently, a considerable proportion of field viruses (75.6%) showed antigenic drift from the existing serotype A vaccine strain A IND 40/2000 necessitating search for an alternate strain. Here, antigenic relationship (‘r₁’ value) of 87 field viruses with each of the 8 candidate strains was estimated by virus neutralization test. A IND 27/2011 strain emerged to be the one with the widest spectrum of antigenic coverage showing ‘r₁’ value of more than 0.3 with 81.6% of field strains. It achieved a reasonably high titre of log₁₀ 7.5 TCID₅₀/ml in BHK-21 suspension cell which was accompanied by positive charge gaining substitutions (E₈₂–K and E₁₃₁–K in VP2) thought to have adaptive significance. However, potency trial remains to be conducted before A IND 27/2011 finds a place in the vaccine formulation.