ISLAMABAD, Pakistan — For years, Pakistan's effort to wipe out the wild polio virus has been thwarted by public fears of foreign vaccines, largely fanned by Islamic clerics and others who warned that polio drops were part of a Western plot to sterilize the Muslim masses.

Today, pockets of resistance to the polio vaccine persist, and Pakistan remains one of only two countries, alongside Afghanistan, where polio has not yet been eradicated.

And yet thousands of Pakistanis, from college students to retirees, have volunteered to be test subjects in coronavirus vaccine trials at five urban hospitals. Since September, about 13,000 of 18,000 volunteers have participated in trials for a Chinese vaccine made by CanSino Biologics. No serious side effects have been reported, and health officials hope to finish the trials and start distributing vaccines by March.

Still, even these volunteers, eager to help while Pakistan faces a resurgence of coronavirus cases and a race against time to begin public inoculations, said they had to overcome personal doubts, frightening social media rumors and opposition from their own families.

“I was aware of people talking about conspiracies, about some chip being inserted into the body, about birth control. Some in my family told me not to do it, but I didn’t care,” said one government employee in his 30s who enrolled in September. “My heart told me to do it. I just pray to God that we get rid of this fatal disease.”

The participant was among eight volunteers recently interviewed by phone in Islamabad and Karachi. All said they had heard the vaccines might be harmful but decided to sign up anyway. All spoke on the condition of anonymity, saying hospital officials had instructed that their identities be kept confidential. Each volunteer is paid $50.

Vaccines from China represent Pakistan’s best hope for inoculating its 233 million citizens in the coming year, officials say. A deeply impoverished country with a tiny health budget, Pakistan has limited hospital space, and many areas have only rudimentary health facilities.

Since the virus first hit, Pakistan has turned to China, its largest foreign economic partner and most important political ally, for help. In the spring, Beijing provided medical equipment and protective gear and sent doctors to help respond to the outbreak. Pakistani officials said the Chinese manufacturer CanSino Biologics is now offering to provide its vaccine at a favorable cost and distribute it on a “priority basis.”

While Pakistan has seen a lower number of coronavirus infections and fatalities than many countries — far fewer than the United States and neighboring India, for example — a new wave of cases has surged in the past several months. On Wednesday, Pakistan passed 10,000 deaths nationwide, and infections rose to 477,000, according to the national health ministry.

Hundreds of thousands of jobs have been lost since the virus arrived in March. The government, while reluctant to order nationwide lockdowns, has enforced repeated temporary local lockdowns, and business activity has plummeted.

Many Pakistanis have ignored government advisories to wear masks and keep social distance, which are aired constantly on radio, TV and mobile phones. This winter, thousands of people, mostly unmasked, have crowded into holiday shopping bazaars and political rallies by opposition parties.

Pakistan is also testing two other Chinese-made vaccines, produced by Sinovac and Sinopharm, but the trials are only in initial stages and far fewer volunteers are registered. The government is part of Covax, the World Health Organization’s system for global cooperation on a vaccine. Pakistani health officials said this will provide free vaccines for about 20­ percent of the country’s population but that they will not be available until the fall of 2021.

Officials said they are in ongoing discussions with other foreign manufacturers and have not made any final decisions, but that so far they prefer the CanSino vaccine, saying it causes fewer side effects than Western-made vaccines, such as BioNTech-Pfizer’s, and can be stored in less extreme cold conditions.

“We are satisfied with the results of CanSino,” said Naseem Salahuddin, head of the infectious diseases department at Indus Hospital in Karachi, which plans to vaccinate about 4,000 volunteers. She said other vaccines being tested are more complicated to use and store. “CanSino suits us,” she said. “This is a one-time injection and we can store it in our refrigerators.”

Javed Akram, vice chancellor of Pakistan’s University of Health Sciences and a member of the national science task force on the coronavirus, said some volunteers who took the BioNTech-Pfizer vaccine had been hospitalized with resulting ailments but that “not a single incident has occurred” in Pakistan’s trials with CanSino. He said vaccine distribution will begin as soon as the trials are successfully completed.

“We will not waste a single minute,” Akram said last week. “The country is losing almost 100 lives daily because of the pandemic.”

But critics say the pace of government testing has been far too slow, and that with more than 2,000 new cases being reported daily, hospitals are starting to fill at an alarming pace. On Dec. 24, Pakistan reported 111 fatalities related to covid-19, the highest single-day death toll during the pandemic’s second wave, further intensifying public pressure on the government.

“The collective response of both federal and provincial authorities has been hugely disappointing in the second wave,” Dawn newspaper said in its lead editorial Sunday. “Pakistan is hurtling towards an abyss as it sleepwalks its way into a crisis that could see its healthcare system collapse.”

Faisal Sultan, the senior Pakistani government adviser on health, told attendees at a news conference that the “burden on hospitals is rapidly increasing” and appealed to the public to take precautions. The manufacturing of vaccines, he said, “is not an excuse for the masses to stop following” health advisories. “We will get the vaccine, but we need to follow safety measures.”

In contrast to those who have failed to take the covid-19 threat seriously, the volunteers allowing themselves to be jabbed with an alien virus are taking a remarkable leap of faith.

In Karachi, a volunteer in his 60s said he initially had “many questions” about the possible impact, and that a friend had sent him a video showing that the vaccine would “turn humans into animals.” But after being vaccinated in October, he experienced only mild side effects, and his wife and two sons then also enrolled.

A housewife in her 20s who was vaccinated at Shifa Hospital International in Islamabad said she had been worried about side effects but that her husband urged her to register “for a good cause.” After being inoculated, she said, “nothing happened, just a little body pain and fever.”

“People are spreading lies on social media that the vaccine is bad and can impact fertility,” the woman said in a telephone interview. “But I believe that without it, the virus will continue to kill people.”

Haq Nawaz Khan in Peshawar, Pakistan, contributed to this report.