A boy reacts as he receives polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa November 10, 2015. (Photo by Khaled Abdullah/Reuters)





A girl receives polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa November 10, 2015. (Photo by Khaled Abdullah/Reuters)





A girl receives polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa November 10, 2015. (Photo by Khaled Abdullah/Reuters)





A woman holds her daughter as she waits for health workers giving polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa, November 10, 2015. (Photo by Khaled Abdullah/Reuters)





A girl reacts as she receives polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa, November 10, 2015. (Photo by Khaled Abdullah/Reuters)





A girl reacts as she receives polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa, November 10, 2015. (Photo by Khaled Abdullah/Reuters)





A boy is being held by relatives as he waits to receive polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa, November 10, 2015. (Photo by Khaled Abdullah/Reuters)





A girl reacts as she receives polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa, November 10, 2015. (Photo by Khaled Abdullah/Reuters)





A man carries his daughter to health workers giving polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa, November 10, 2015. (Photo by Khaled Abdullah/Reuters)





A girl receives polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa, November 10, 2015. (Photo by Khaled Abdullah/Reuters)





A girl looks after she received polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa, November 10, 2015. (Photo by Khaled Abdullah/Reuters)





A boy is being held by his sister as he waits to receive polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa, November 10, 2015. (Photo by Khaled Abdullah/Reuters)





A girl holds her father's hand after she received polio vaccine drops during a house-to-house vaccination campaign in Yemen's capital Sanaa, November 10, 2015. (Photo by Khaled Abdullah/Reuters)