Final answer:
RNA viruses, such as HIV, enter cells via fusion proteins. For prophylaxis in high-risk infants, preventive measures are important as there are currently no specific antiviral therapies or vaccines available for viral pneumonia caused by RNA viruses like RSV.
Step-by-step explanation:
Viruses with complex life cycles, such as HIV, enter cells via fusion proteins. For example, HIV attaches to a cell surface receptor and fuses with the cell membrane, allowing viral contents to be released into the cell. This process helps the virus hide within the host cell's genome and contributes to the rapid development of antiviral drug resistance.
In terms of prophylaxis for high-risk infants, there are currently no specific antiviral therapies or vaccines available for viral pneumonia caused by RNA viruses like RSV. However, preventive measures such as reducing exposure to respiratory droplets and maintaining good hygiene practices can help reduce the risk of infection in high-risk infants.