Differences in the priming effect of various clades/subclades of inactivated H5N1 vaccine for booster injection with heterologous clades of vaccine strains.

The prime-boost response induced by different combinations of four H5N1 vaccines (NIBRG-14 (clade 1), Indo05/2005(H5N1)/PR8-IBCDC-RG2 (clade 2.1), A/Bar-Headed Goose/Qinhai Lake/1A/05 SJ163222 (clade 2.2), and Anhui01/2005(H5N1)-PR8-IBCDC-RG5 (clade 2.3.4)) was evaluated in mice. Clade 1-primed BALB/c mice showed a booster response to all of the other three H5N1 vaccines. Clade 2.2 vaccine was also a good priming vaccine. However, mice primed with clade 2.1 or clade 2.3.4 vaccine did not respond to booster injection with clade 1 vaccine, suggesting that priming might actually inhibit the booster response with some combinations of vaccines belonging to different clades. Analysis of the mechanism involved showed that lymphocytes from primed mice secreted comparable amounts of cytokines with any combination of priming and booster vaccines. Therefore, impairment of B cell immunity specific to certain booster strains may have been involved.

A prime-boost vaccination of mice with heterologous H5N1 strains.

We evaluated the priming effect of an H5N1 pandemic vaccine in a mouse model to investigate strategies for influenza pandemic vaccination. For priming, an alum-adjuvanted inactivated whole H5N1 vaccine (NIBRG-14, clade 1) was used. As booster vaccines, several formulations of Indo05/05/2005(H5N1)PR8-IBCDC-RG2 vaccines (clades 2-1)were evaluated, including split, whole, alum-adjuvanted split, and alum-adjuvanted whole vaccines. Any type of booster vaccination elicited a significant HI antibody response despite the difference in antigenicity between the priming and booster vaccines. The split vaccine elicited a much stronger booster response than the alum-adjuvanted whole vaccine. When the mice were primed with the H1N1 or H3N2 vaccines, this did not affect the booster response to the H5N1 vaccine. These results indicated that an alum-adjuvanted whole vaccine is able to confer immunological memory to haemagglutinin even if the primed and boosted vaccine strains are in different clades and, once vaccinated, a split vaccine is preferred to evoke recall responses.

Timely production of A/Fujian-like influenza vaccine matching the 2003-2004 epidemic strain may have been possible using Madin-Darby canine kidney cells.

Timely production and antigenic match with those of the epidemic strains are required for influenza vaccines. A/Fujian/411/2002-like (H3N2) virus was the main epidemic influenza virus during the 2003/2004 season in the northern hemisphere. But A/Fujian-like reassortant viruses were not available until more than one year later. We evaluated the A/Kumamoto/102/2002 strain, an A/Fujian/411/2002-like strain isolated in 2002, as a potential vaccine. We compared A/Kumamoto/102/2002 viruses isolated from the same clinical sample in Madin-Darby canine kidney (MDCK) cells and eggs. Kumamoto/102/2002 isolated from eggs grew poorly and showed amino acid mutations of haemagglutinin. In contrast, A/Kumamoto/102/2002 isolated from MDCK cells grew well in MDCK suspension culture. The amino acid sequence of MDCK-derived A/Kumamoto virus was identical to that of A/Fujian/411/2002. These results suggest that culture in MDCK cells could have produced an influenza vaccine with a better antigenetic match to the predicted epidemic strain for the 2003/2004 season than the vaccine actually produced.

Effects of several virucidal agents on inactivation of influenza, Newcastle disease, and avian infectious bronchitis viruses in the allantoic fluid of chicken eggs.

General theories on the inactivation of viruses in the presence of a concentrated protein, such as the allantoic fluid of chicken eggs, are not useful. That is, although sodium hypochlorite and sodium hydroxide are generally known as strong virucidal agents, they do not sufficiently inactivate viruses in allantoic fluid. We found that benzalkonium chloride (BC) is an effective virucidal agent against influenza, Newcastle disease, and avian infectious bronchitis viruses even in the presence of a concentrated protein. BC is easily biodegradable by activated sludge and is not very harmful to humans. We strongly recommend BC as a useful virucidal agent, especially in the manufacture of vaccines for these viruses.