Requirements for vaccines: Historically, in most countries, vaccines specifically designed to
contain or prevent HPAI were banned or discouraged by government agencies because they may
interfere with stamping-out control policies. The first use of vaccination in an avian influenza
eradication programme was against H5/H7 LPAI. The programmes used inactivated oil-emulsion
vaccines with the same haemagglutinin and neuraminidase subtypes as the circulating field virus,
and infected flocks were identified by detection of virus or antibodies against the virus in nonvaccinated
sentinel birds. During the 1990s the prophylactic use of inactivated oil-emulsion
vaccines was employed in Mexico and Pakistan to control widespread outbreaks of HPAI and
H5/H7 LPAI, and a recombinant fowl poxvirus vaccine expressing the homologous HA gene was
also used in Mexico, El Salvador and Guatemala. During the 1999–2001 outbreak of H7 LPAI in
Italy, an inactivated vaccine was used with the same (i.e. homologous) haemagglutinin subtype to
the field virus, but with a different (i.e. heterologous) neuraminidase. This allowed the serological
differentiation of non-infected vaccinated birds from vaccinated birds infected with the field virus
and ultimately resulted in eradication of the field virus. Prophylactic use of H5 and H7 vaccines has
been practised in parts of Italy, aimed at preventing H5/H7 LPAI infections, and several countries in
Asia, Africa and the Middle East as an aid in controlling H5N1 HPAI virus infections. HPAI viruses
should not be used as the seed virus for production of vaccine.