Effects of original antigenic sin on the immune response to inactivated influenza A virus subtype H5N1 vaccine
Objective 
To investigate the effects of original antigenic sin caused by previous exposure to influenza A virus subtype H1N1 on the immune response to inactivated H5N1 vaccine. 
 
 
Methods 
In this study, the BALB/c mice were first infected with A/PR8 (H1N1) virus or immunized with inactivated vaccine to induce immune responses against the A/PR8 virus. Then they were injected once with inactivated H5N1 vaccine at dosages of 0.01 μg, 0.1 μg and 1 μg, respectively. The levels of IgG and neutralizing antibodies in serum samples were detected after immunization. Four weeks after immunization, the mice were challenged with a lethal dose of H5N1 virus. Some indicators including the survival rate, body weight loss and residue virus titer in lung were recorded for further evaluation. 
 
 
Results 
The pre-existing anti-A/PR8 antibodies in mice didn′t alleviate the immune responses to inactivated H5N1 vaccine. 
 
 
Conclusion 
This study indicates that the original antigenic sin associated with the previous exposure to A/PR8 virus has no significant effect on the immune efficacy of H5N1 vaccine. 
 
 
Key words: 
Influenza vaccine; Original antigenic sin; Influenza A virus subtype H5N1