Both ELISA and EIA are synonyms and exactly the same. For
HIV, we do 4th generation Combo test, which detects HIV antibody by ELISA, and the p24 antigen. This increases the sensitivity and specificity of the test, and decreases the window period. The window period is 3 months for HIV.
Nowadays all labs are doing the HIV Combo test only.
Next Steps
You have to do
HIV ELISA/EIA test at these intervals following exposure - on day 0, 6 weeks, 3 months and 6 months.