Sexually transmitted infections (STIs), including HIV and Aids, are to be included in the new GCSE curriculum as a result of pressure from sex education organisations.

The new science curriculum for key stage 4 (KS4) has been revised to include lessons on sexual health and information about HIV and Aids. But experts say that these will only be effective if they build on lessons taught well before the final years of secondary school.

In a newly published amendment to the GCSE curriculum, the Department for Education states that the changes “support the Government’s ambition to build knowledge and resilience about sexual health among young people…It is important that young people are taught all aspects of sex education.”

Previously, sexual health and STIs were included only in the KS3 science curriculum. However, the original draft of the new national curriculum made no mention of sexually transmitted diseases, either at KS3 or KS4.

The Sex Education Forum, which is part of the National Children’s Bureau charity, voiced concern about this absence. “The proposals will lead to some young people missing out on vital sexual health information,” it said.

As a result, the government has amended the proposed GCSE curriculum, which will come into effect from September 2016. In addition to learning about HIV, Aids and other sexually transmitted diseases, students will be taught about different forms of contraception. This will build on earlier discussion about human reproduction, at KS3.

But the Sex Education Forum expressed fears that, by failing to mention sexual health until students are 15, schools will prevent teenagers from building up a proper understanding of safe sex.

A spokeswoman said: “Learning about STIs must not be left to the final years of secondary school, and will only be effective if it builds on earlier learning about how our bodies work and, crucially, about relationships.”

She insisted that the biological aspects of disease transmission, prevention and treatment must be coupled with ongoing education about sex and relationships.

Jane Lees, chair of the Sex Education Forum, said: “We will continue to campaign for action to make the broader subjects of sex and relationships education statutory in all schools.”