A contraceptive that blocks male fertility has come closer with a study showing that it is possible to inoculate monkeys against their own sperm.

A contraceptive that blocks male fertility has come closer with a study showing that it is possible to inoculate monkeys against their own sperm.

According to the journal Science , scientists have developed a prototype vaccine that causes the immune system of monkeys to launch an attack on a key protein in the testes, eppin, which is involved in the activation of sperm cells.

Tests on a group of male macaque monkeys shows that the vaccine induced temporary infertility for up to a year when booster injections were given once every three weeks.

However, two of the nine monkeys did not respond to the vaccine and two more did not regain their fertility during the lifetime of the experiment, said Michael O'Rand of Duke University in Durham, North Carolina.

"It seems to be really possible to make a contraceptive male vaccine in non-human primates," Dr O'Rand said.