Sunday is World AIDS Day, and there is much to celebrate but also much to frighten.

Sunday is World AIDS Day, and there is much to celebrate but also much to frighten.

The World Health Organization has stated the theme of this year’s observance, in fact the theme of every World AIDS Day from 2011 through 2015, is "Getting to zero: Zero new HIV infections. Zero discrimination. Zero AIDS-related deaths."

That goal would have seemed unimaginable just a few years ago. But prevention, detection and treatment have brought those goals within sight. The special focus of this year’s WHO campaign is improving access to prevention, treatment and care services for adolescents.

That’s the scary part: Adolescents from 10 to 19 years continue to be especially vulnerable to HIV and AIDS.

Don’t think that’s a problem just in other parts of the world. In the United States one in four new HIV infections occurs in youths 13 to 24, according to the Centers for Disease Control and Prevention. Statistics from 2010 showed 1,000 new cases of HIV in youths each month. About 7 percent of those with HIV are youths, and about 60 percent of those young people with HIV don’t know it, are not being treated for it, and can unknowingly pass the virus onto others.

Primarily these young people are infected when they start having sex or when they start injecting drugs. Males account for 80 percent of new infections, and African-American boys and young men account for 60 percent of new infections.

Risk for getting HIV is higher in communities where it is already prevalent, according to the CDC. African-Americans have a greater burden of HIV infection than any other racial or ethnic group, so the risk of young people in the group contracting the virus is higher. Likewise gay and bisexual men are 40 times more likely to get HIV than other men, and fewer than half of gay and bisexual males in high school used condoms the last time they had sex, according to the CDC.

Still we know we can halt HIV. Globally the number of new HIV infections continues to fall. 2012 saw the lowest number of new infections — 2.3 million — since the mid-to-late 1990s. In 26 countries the number of infections declined by more than 50 percent from 2001 to 2012, and another 17 countries saw infections fall by 25 percent to 49 percent, according to UN AIDS.

A large part of that is effective and affordable antiretroviral therapy. Drugs that cost $10,000 per person, per year in the mid-’90s costs just $140 in some low- to middle-income countries. The number of people with access to treatment has increased exponentially in recent years.

A remarkable change has been the understanding that pregnant women with HIV who have access to antiretroviral medicines can reduce the chances of passing the infection on to their babies to 5 percent or less. In some countries hard hit by AIDS, like Rwanda and Sierra Leone, as many as 80 percent of HIV-positive women have access to those drugs.

But everywhere gender-based violence and HIV are connected in tragic ways. Fifty young women an hour are newly infected with HIV, often at the hands of violent intimate partners, according to UN AIDS. Globally, female drug users, female sex workers and transgender women are especially likely to experience violence, but any women in a conflict-affected situation from Sudan to Syria to Egypt are vulnerable to rape and HIV infection.

So as World AIDS Day dawns, we find ourselves in a world where our ability to halt HIV and AIDS is increasing everyday, but many challenges remain. Science is doing its job; now we must do ours.

In our own country, we need to make sure young people are getting the word about AIDS, what causes it and how it can be prevented. We parents, teachers, doctors, coaches, counselors must have frank talk with the young people in our lives even if it makes us uncomfortable. The cost is just too high not to.

We need also to support global efforts to get good information to those at risk of HIV and good therapies to those already infected. We need to work to bring peace or at least order to the corners of our world where peace and order seem least possible. We need to eliminate violence against children and women. After all, as recently as 10 years ago it was hard to imagine a world where the threat of AIDS was decreasing, and now we live in that world. That’s proof that we can do unimaginable things.