The reliability of Soviet space vehicles stood at 50 percent, with three of six test flights ending in a flop in the early 1960s. On May 15, 1960, a reentry module failed to land on Earth in a mishap that was followed by a launch pad explosion of a spacecraft with dogs Damka and Krasavka on board on September 23, 1960.

A father of two, Yuri Gagarin was tipped to be finally replaced with childless German Titov, however, this never saw the light of day. Chief Designer Sergei Korolev played the key role in this decision , insisting that it is Gagarin who should be the first man in outer space. For their part, medics refused to sign a document confirming assurances of safety for Gagarin before, during and after the flight.

The Soviet Mission Control Center, which did not have space TV, recorded at least 40 kilometers of tape when communicating with Yuri Gagarin on April 12, 1961. The “top-secret” tape is currently under lock and key.

During the first twenty seconds of launch, Gagarin’s life was at especially high risk given that no rescue steps were stipulated for this period. In case of a blast, he was instructed to eject himself from the spaceship, a decision that was to be made by the Mission Control Center.

Upon being catapulted, Gagarin was to be salvaged by four beefy guards with the help of a nylon lifesaving net.

http://www.astronautix.com/flights/vostok1.htm#more

My point is that Nasa would not have taken this kind of risk. The whole operation of Yuri's first space flight was riddled with extreme risk including ejecting from the capsule after rentry to avoid a crash landing.

That being said, Russia IMO has the best safety record for human spaceflight with the Soyuz spacecraft which is testament to simplicity, but has it limits in payload and versatility.