Yes. Plastic condoms are as effective as latex condoms when it comes to protection against STDs and HIV infections. These condoms are meant for those men and women who are allergic to latex condoms.
Thou FDA (US) approved plastic condoms, the effectiveness of them is not fully ascertained as of now, as the user base is very limited as of now. Condoms made of animal skin such as lambskin (called natural skin condoms) have proven to be ineffective in preventing STDs including HIV.