Malaysia Airlines flight MH17 was flying over eastern Ukraine's Donetsk region on Thursday when it was blasted by a surface-to-air missile. The exploded aircraft crashed and brought down with it all 298 people on board and a significant share of humanity's ability to fight and end the HIV and AIDS epidemic.  

On board the plane and among those who perished were researchers and activists bound for an international conference in Melbourne, Australia, where they would have gathered to learn ways to combat HIV and AIDS, which remain prevalent and continue to claim about 1.5 million lives per year.

Although it isn't yet clear how many delegates to the 20th International AIDS Conference, which is scheduled to start on Sunday, died on the MH17 crash, President Barack Obama has described their death as a significant loss.

"These were men and women who had dedicated their own lives to saving the lives of others, and they were taken from us in a senseless act of violence," Obama said on Friday.

In his statement, Obama said that there were about 100 researchers and advocates on board MH17 but organizers of the conference said they have only confirmed seven so far.

"We have been working hard to try and confirm how many people were on the flight," said Chris Beyrer, incoming president of the International AIDS Society (IAS). "We've been speaking to a number of different authorities, and we think the actual number is much smaller."

Among those confirmed dead was Joep Lange, a clinical researcher specializing in HIV therapy. Lange, who was president of IAS from 2002 to 2004, had participated in works that paved way to the use of multiple drugs instead of just a single medication for suppressing HIV.  The therapy now used by millions of people worldwide to treat HIV infection involves taking a combination of drugs.

Lange also advocated to make HIV treatment more affordable and accessible to patients in developing nations. Michael Kessler, from the IAS, said that the AIDS movement has lost a giant with the passing of Lange.

Martine de Schutter, program manager of Bridging the Gaps, an international HIV program, also died in the crash along with Pim de Kuijer, from the Stop AIDS Now group and HIV/AIDS prevention advocate Lucie van Mens.

Lange's partner, Jacqueline van Tongeren, Amsterdam Institute for Global Health and Development's director of communications, who had also been involved in AIDS-related work for nearly two decades, also died in the plane crash.