(CNN) From climate change to superbugs, the World Health Organization has laid out 10 big threats to our global health in 2019.

And unless these threats get addressed, millions of lives will be in jeopardy.

Here's a snapshot of 10 urgent health issues, according to the United Nations' public health agency:

Not vaccinating when you can

One of the most controversial recent health topics in the US is now an international concern.

"Vaccine hesitancy -- the reluctance or refusal to vaccinate despite the availability of vaccines -- threatens to reverse progress made in tackling vaccine-preventable diseases," WHO said.

"Vaccination is one of the most cost-effective ways of avoiding disease -- it currently prevents 2-3 million deaths a year, and a further 1.5 million could be avoided if global coverage of vaccinations improved."

The health agency cited the recent 30% global increase in cases of measles -- a disease that had been nearly wiped out in some countries.

"The reasons for this rise are complex, and not all of these cases are due to vaccine hesitancy," WHO said. "However, some countries that were close to eliminating the disease have seen a resurgence."

Drug-resistant superbugs

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There's a dark side to the incredible success of antibiotics, antivirals and antimalarials: Overuse of such treatments have led to drug-resistant superbugs.

"Now, time with these drugs is running out," WHO said.

"Antimicrobial resistance -- the ability of bacteria, parasites, viruses and fungi to resist these medicines -- threatens to send us back to a time when we were unable to easily treat infections such as pneumonia, tuberculosis, gonorrhea, and salmonellosis."

About 1.6 million people die each year from tuberculosis, and many patients suffer because antibiotics don't work.

"In 2017, around 600,000 cases of tuberculosis were resistant to rifampicin -- the most effective first-line drug -- and 82% of these people had multidrug-resistant tuberculosis," WHO said.

The agency said it's working on a plan to fight antimicrobial resistance by increasing awareness, reducing infection and encouraging cautious use of such drugs.

Air pollution and climate change

Polluted air kills 7 million people every year and about 90% of people now breathe it, WHO said.

"Microscopic pollutants in the air can penetrate respiratory and circulatory systems, damaging the lungs, heart and brain, killing 7 million people prematurely every year from diseases such as cancer, stroke, heart and lung disease," the agency said.

"The primary cause of air pollution (burning fossil fuels) is also a major contributor to climate change."

The UN agency said between 2030 and 2050, "climate change is expected to cause 250,000 additional deaths per year, from malnutrition, malaria, diarrhea and heat stress."

Climate change can also lead to extreme drought -- which is one reason why many Central Americans are fleeing to the United States

Another global flu pandemic

WHO said it believes the world "will face another influenza pandemic -- the only thing we don't know is when it will hit and how severe it will be."

In the United States alone, at least 13 children have died from the flu this season.

This year's predominant strain, H1N1, is also known as swine flu. It disproportionately affects children and adults under 50, said Dr. William Schaffner, a professor at Vanderbilt University Medical Center.

He said that's because similar strains were circulating about 40 to 50 years ago.

"Older people may have been infected with cousins of H1N1 years ago, and that gives them residual protection," Schaffner said.

WHO said it's constantly monitoring the circulation of flu viruses to detect potential pandemic strains. It said 153 institutions in 114 countries are involved in global surveillance and response.

Crises in vulnerable places

Over 1.6 billion people -- more than 1/5 of the world's population -- live in areas of sustained crises such as drought, famine, conflict and displacement, WHO said.

More than a million Syrians fleeing a gruesome civil war have sought refuge in Lebanon, only to find themselves in peril again.

Devastating floods and frigid temperatures have brought more misery and death to refugees living in makeshift camps.

An 8-year-old Syrian refugee recently died during a storm after the girl fell into a river and drowned.

High-threat pathogens like Ebola

Just when we thought Ebola was mostly under control, two separate Ebola outbreaks ravaged parts of the Democratic Republic of the Congo last year.

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Both outbreaks spread to cities of more than 1 million people, the UN health agency said.

"This shows that the context in which an epidemic of a high-threat pathogen like Ebola erupts is critical -- what happened in rural outbreaks in the past doesn't always apply to densely populated urban areas or conflict-affected areas," WHO said.

In addition to Ebola, scientists are prioritizing on several other hemorrhagic fevers, Zika, Nipah, Middle East respiratory syndrome coronavirus (MERS-CoV) and Severe Acute Respiratory Syndrome (SARS), WHO said .

Non-transmissible diseases

While there are plenty of fears about contagious diseases, more than 70% of all deaths worldwide are from non-transmissible diseases such as cancer, diabetes and heart disease.

"This includes 15 million people dying prematurely, aged between 30 and 69," WHO said.

"The rise of these diseases has been driven by five major risk factors: tobacco use, physical inactivity, the harmful use of alcohol, unhealthy diets and air pollution."

Dengue

Something as simple as a mosquito bite can turn deadly in cases of dengue, which "has been a growing threat for decades," WHO said.

"An estimated 40% of the world is at risk of dengue fever, and there are around 390 million infections a year," WHO said.

Dengue causes flu-like symptoms and can kill up to 20% of those with severe cases, the agency said.

"A high number of cases occur in the rainy seasons of countries such as Bangladesh and India. Now, its season in these countries is lengthening significantly ... and the disease is spreading to less tropical and more temperate countries."

Weak primary health care

While those with good insurance often take health care for granted, the lack of adequate primary care is rampant in many parts of the world

"Primary health care can meet the majority of a person's health needs of the course of their life," WHO said. "Yet many countries do not have adequate primary health care facilities."

HIV

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The good news: We've made a lot of progress in terms of HIV testing and treatment. About 22 million people are currently getting treated for HIV, WHO said, and others who are at risk of getting HIV are taking antiretroviral medications to prevent getting infected.

"However, the epidemic continues to rage with nearly a million people every year dying of HIV/AIDS," WHO said.

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About 37 million people around the world are living with HIV, the agency said.

"A group increasingly affected by HIV are young girls and women (aged 15--24), who are particularly at high risk and account for 1 in 4 HIV infections in sub-Saharan Africa despite being only 10% of the population," WHO said.

The agency said this year it will work with countries to promote self-testing so people who have HIV can learn their status and get treatment.

WHO and the International Labour Organization will also support companies and organizations to offer HIV self-tests in workplaces.