The vaccination coverage required to establish herd immunity against influenza viruses.

OBJECTIVE

1. To determine the influenza vaccination coverage required to establish herd immunity, and 2) to assess whether the percentages of vaccination coverage proposed and those registered in the United States and Europe are sufficient to establish herd immunity.

METHODS

The vaccination coverage required to establish herd immunity was determined by taking into account the number of secondary cases per infected case (R(o)) and the vaccine effectiveness.

RESULTS

The required percentage that would have been required to establish herd immunity against previous influenza viruses ranged from 13% to 100% for the 1918-19, 1957-58, 1968-69 and 2009-10 pandemic viruses, and from 30% to 40% for the 2008-09 epidemic virus. The objectives of vaccination coverage proposed in the United States - 80% in healthy persons and 90% in high-risk persons - are sufficient to establish herd immunity, while those proposed in Europe - only 75% in elderly and high-risk persons - are not sufficient. The percentages of vaccination coverage registered in the United States and Europe are not sufficient to establish herd immunity.

CONCLUSION

The influenza vaccination coverage must be increased in the United States and Europe in order to establish herd immunity. It is necessary to develop new influenza prevention messages based on herd immunity.