CHICAGO (Reuters) - A Zika vaccine Sanofi SA dropped in September under political pressure over pricing produced strong responses in more than 90 percent of those taking part in an early-stage clinical trial, U.S. researchers reported on Monday.

FILE PHOTO: The logo of French drugmaker Sanofi is seen in front of the company's headquarters in Paris, France, March 8, 2016. REUTERS/Philippe Wojazer/File Photo

The results, published in the journal Lancet, offer a first glimpse at the vaccine’s performance in people, and suggest it might have had a promising future.

The interim findings do not guarantee the vaccine would work, but the “immune response data in humans are very promising,” said Dr. Dan Barouch, a vaccine researcher at Harvard-affiliated Beth Israel Deaconess Medical Center in Boston, where one of three trials of the vaccine are taking place.

In February 2016, the World Health Organization declared the Zika outbreak in Brazil and elsewhere an international public health emergency because of the link between the virus and severe birth defects, touching off a scramble for a vaccine.

WHO has since downgraded the threat, but the mosquito-borne virus remains a public health concern, especially for pregnant women.

The ZPIV vaccine, made from inactivated Zika virus particles, was developed by U.S. Army researchers, who in July 2016 had agreed to give Sanofi an exclusive license to complete testing and bring the product to market.

The deal hit a snag in March when Vermont Senator Bernie Sanders and other lawmakers wrote letters urging Army officials to cut a more favorable deal for the vaccine developed with taxpayer money.

In July, Sanders proposed a rule to end “price gouging on taxpayer-funded products” by requiring federal agencies to secure agreements that such products will be reasonably priced.

Dr. Amesh Adalja, a senior associate at the Johns Hopkins Center for Health Security, said accusations like those by Sanders could have a chilling effect on companies’ decisions to partner with U.S. government scientists during epidemics.

“Emerging infectious diseases such as Zika are not the same thing as making a pill for cholesterol. It’s a very limited market,” he said.

In August, the Biomedical Advanced Research and Development Authority (BARDA), the development arm of the Department of Health and Human Services, pulled funding for clinical development of the ZPIV vaccine.

At the time, Sanofi cited BARDA’s decision, along with the difficulty in staging human clinical trials during the waning days of the Zika epidemic, as reasons for its decision to drop development of the vaccine.

Sanofi spokeswoman Ashleigh Koss said developing vaccines for emerging infectious disease is “a high-risk endeavor.”

“We have been clear about the importance of public-private partnerships in addressing emerging infectious diseases like Zika and believe it is essential for vaccine manufacturers to collaborate with governmental scientific organizations,” she said in an email on Monday.

BARDA is continuing to back several Zika vaccines, including one similar to ZPIV from Takeda Pharmaceutical Co. Takeda last week said it had begun a Phase 1 trial with results expected next year.

“They are essentially the same type of a product,” said Dr. Anthony Fauci, director of the National Institutes of Allergy and Infectious Disease, in a phone interview on Monday. “The only thing is Takeda owns it so there isn’t the issue of the government giving them an exclusive license.”

Colonel Nelson Michael of the Walter Reed Army Institute of Research said by email on Monday that the Army was exploring licensing the ZPIV vaccine to other companies.