After more than 30 years of attempts, there may be a promising advance in the search for a vaccine for HIV, the virus that causes AIDS if left untreated.

Now, preliminary data from an early stage clinical trial out of the International AIDS Vaccine Initiative and The Scripps Research Institute in La Jolla, California, suggests that a new HIV vaccine may hold promise.

"These are very early studies. But nonetheless, they are provocative," said Dr. William Schaffner, a professor of preventative medicine and infectious diseases at Vanderbilt University in Nashville, who was not involved in the clinical trial.

Although the vaccine candidate will still need to be tested in larger studies, experts are hopeful this vaccine might succeed where others have failed.

"This is a very innovative approach to developing a vaccine that hasn't been done before," Schaffner said, who described the underlying vaccine technology as "kind of a culmination of 21st century science."

When HIV was first discovered as the cause for AIDS in the early 1980s, researchers thought that a vaccine for this virus could be created rapidly, as had been done for diseases like measles, chickenpox and hepatitis B. In fact, the then-U.S. secretary of health and human services, Margaret Heckler, predicted in 1984 that a vaccine would be available in two years. Researchers soon found that there were more hurdles than they had initially thought.

HIV is a virus that mutates rapidly, creating a moving target for vaccines. HIV also has many different subtypes, so a vaccine offering protection against one subtype of HIV may be ineffective against another.

The new research out of IAVI and Scripps aims to address these difficulties by developing a vaccine that helps the body create "broadly neutralizing antibodies." The researchers hope to stimulate a person's immune system against many HIV variants and mutations.

This research is based on "identification of a subset of HIV-infected individuals ... who, in the course of their infection, do make so-called broadly neutralizing antibodies, which basically means these antibodies are able to potently block infection of diverse HIV variants, and that is the key goal," said Dr. Mark Feinberg, Ph.D., the CEO of IAVI.

Their early stage, phase 1 clinical trial, which is still underway, involved 48 healthy adults who received a total of two doses of either the vaccine or placebo, two months apart. Preliminary data showed 97% of those who received the vaccine had early evidence that their immune system may be able to make these broad antibodies.

"The broadly neutralizing antibody is important, because the virus can mutate so rapidly that they need something that's a shotgun, not a rifle ... to prevent a whole variety of different kinds of HIV configurations," said Schaffner.

The decadeslong search for an HIV vaccine lies in stark contrast to the development of vaccines for COVID-19, "where the science was ready, and we were able to develop vaccines, plural, very, very quickly," Schaffner added.

The researchers at IAVI and Scripps are collaborating with companies, like Moderna, to harness the mRNA technology used in the development of vaccines against COVID-19.

Sara Yumeen, M.D., is a preliminary-year internal medicine resident at Hartford Healthcare St. Vincent's Medical Center in Connecticut and is a contributor to the ABC News Medical Unit.

The reproductive years for women in the United States may be increasing, according to a new study.

On average, the reproductive years for women increased from age 35 to 37.1, according to the study published Wednesday in the Journal of the American Medical Association.

The age of 35 has for decades been regarded in the medical community as the age when women's reproductive systems slow down and it becomes more difficult to have and sustain a pregnancy. Women who become pregnant at age 35 and above are considered of advanced maternal age and face risks including miscarriage, genetic abnormalities, fetal growth issues, preterm birth, preeclampsia and stillbirth, experts say.

Giving birth later in life is a growing reality in the U.S. though. Since 2007, the birth rate has risen 19% for women in their early 40s, 11% for women in their late 30s and just 2% for women in their early 30s. Birth rates for women in their 20s declined from 2015 to 2016, according to the Centers for Disease Control and Prevention.

The new study that found women's reproductive span now extends to 37 years of reproductive years, on average, looked at 60-year trends in age at natural menopause and reproductive life span and other factors among U.S. women. This increase in reproductive years may be a result of later ages of menopause and earlier ages of first period, on average.

The data showed that average age of menopause for women increased, from 48.4 years to 49.9. And the age that a girl got her first period dropped slightly, on average, from 13.5 years to 12.7.

"These are important numbers," said Dr. Jennifer Ashton, ABC News chief medical correspondent and a board-certified OBGYN. "It's good to get a grip on what's happening over a woman's reproductive life."

The changes in women's reproductive life spans could have potential implications for cases of both heart disease and cancer in women, according to Ashton.

She said the broadening of the life span could mean a slight decrease in cardiovascular disease among women, but could raise the risk of breast cancer, ovarian cancer and endometrial cancer, also known as hormonally responsive cancers.

"The more hormonal stimulation [there is] across a woman's lifetime, those cancers can go up," explained Ashton.

The milestone reproductive moments in women's life spans also come with side effects, which range from mild to severe, according to Ashton.

The side effects can range from fatigue and cramping on the mild end to mood changes, severe pelvic pain and heavy bleeding on the more severe end, according to Ashton. Women may also experience irregular menstrual cycles, changes in sleep patterns, and hot flashes in the years leading up to menopause, which is when women stop having menstrual periods.

"We have to remember these milestones in life, while natural, can be problematic," she said. "There's a range of symptoms."