ReactJs Checkbox - cannot uncheck

I am trying to set the checked prop of a checkbox using a state, updated code with handleChange function:

getInitialState: function() {
    return {
        selected:0,
        contactId: 0
    };
},

handleChange: function(e) {
    var id = this.state.contactId;

    console.log(e.target.checked);

    if (e.target.checked === true){

        console.log('selected');

        contactChannel.publish({
                    channel: "contact",
                    topic: "selectedContact",
                    data: {
                        id: [id]
                    }});

    } else{

        basketChannel.publish({
            channel: "basket",
            topic: "removePersonFromBasket",
            data: {
                id: [id]
            }
        });


        console.log('deselected flag');


    }
},
render: function() {

    var id = this.state.contactId;
    var isSelected = this.state.selected;

    console.log(isSelected);

    return (
        <div className="contact-selector">
            <input type="checkbox"
                   checked={isSelected}
                onChange={this.handleChange} />
        </div>
    );
}

However, once the checkbox is checked by default I cannot uncheck it, can anyone please tell me how to do this?

Many thanks