One billion people lives in developing countries and over 2B with less than $2 per day. Lack of skills in healthcare leads to shortage on this, even for basic cases. The Millennium Development Goals was created by United Nations to start from the basics. Strenghten national capacity and infrastructures, facilitate access to treatments, make tratments and medicines available to people, set additional fundings and check that these are well delivered, keep searching in research and development to innovate critical treatments (e.g. HIV) and expand its spread. Technology can help starting with access to doctor and diagnosys even if this could be the first barrier as sometimes communication is not easy too.

Infectious diseases if one of the major issue that most public health department is facing in developing countries. Thus, low cost screening method such as cheap microscope (for example the fold able 1 dollar microscope) does helps to save a lot of lives (to screen for malaria in blood sample and cholera in stool sample)!

Accessibility Of The Digital Future Of Health Innovations Will Drive Development. As We Connect Cheap Wearables To Our Phones, along With The IoT Devices Themselves... Info Sharing and The Incentives That Reward Patients For Sharing Their Health Related Data/Information Will Be The Catalyst...IMO ;)

I think low-cost innovation is the first need of underdevelopment countries. However, low quality of life and pollution are a major factor in health issues. Innovation towards things like senetation, hygiene, water purification, and cleanings can save a lot of lives. 

Accessibility to health care is another issue in most developing countries. Even though there is a lack in expertise and medication but the accessibility to health care services is even lower. Imagine if someone need to travel more than 24hr just to reach the nearest clinic to receive basic health care,this will sure to act as a hindrance for one to seek healthcare services!

Gastroenterisits is a common issue in most developing countries that causes millions of life, poor quality of life and financial loss. Accessible to clean water is not as easy as other developed countries. Some time even accessible to water itself is an issue. Pathogen that could cause gastroenteritis are usually water born especially Cholera. This issue could be solve by providing cheap and user friendly filters to those area in need and oral dehydration salt to those area!

HIV in USA?

Not even close domestically.
Cause of death rankings: 

1- Swine flu
2- Drugs
3- Hand-guns