13.But cases of the type two virus have not been seen in years . And the new study confirmed that the type two vaccine reduces the effectiveness of the other vaccines when given together.
14. To avoid that problem , the new combination contains vaccine only for the type one and type three polio viruses.
15. And that's the VOA Special English Health Report. For more health news, go to voaspecialenglish . com. You can also find
captioned videos of our reports on the VOA Learning English channel on YouTupe. I'm Steve Ember