That Monday marked the start of an ambitious, three-day vaccination drive aimed at inoculating some 34 million Pakistani children against polio, the crippling disease eradicated in almost the entire world, yet still transmitted there.
But that day also marked the start of a determined campaign of murder — at least nine people were killed — against the very health workers trying to save children's lives.
It was a campaign rooted in a belief that these workers are out to harm the children they are trying to inoculate. Such misinformation is actively encouraged by Sunni Muslim extremists like the Pakistan Taliban, the presumed culprit in the attacks, though the group denies involvement.
Ultimately, the mistrust hurts children in some of Pakistan's most vulnerable and hardest to reach communities — and threatens to spread the harm far beyond by keeping the poliovirus alive.
Frustrated by the attacks, and the halting progress towards what the UN calls the "historic goal" of eradicating polio worldwide, the World Health Organization has now turned to one of Sunni Islam's highest authorities for advice and help.
The grand imam of Al Azhar mosque and university in Cairo took up the matter, and earlier this month, hosted WHO officials, along with a number of high-ranking religious scholars from several Muslim countries, to try to come up with a new strategy to counter the Taliban's lies.
On the table was everything from sending clerics into the field with health workers to help allay local concerns to a media campaign to dispel the rumours that the vaccine is harmful.
After two days of meetings, this group believes that, despite the challenges, polio can be eradicated in less than two years.
The UN vowed in 1988 to eradicate polio worldwide, and that goal is tantalizingly close to being realized.
According to WHO, Pakistan is one of only three countries where the war against polio still rages — the others are Afghanistan and Nigeria.
However, the wild poliovirus's persistence in those places can be a threat to children anywhere, no matter how long their countries have been polio-free.
China, for example, experienced an outbreak in 2011 after 12 years without cases. And in January, the strain in Pakistan was found in the sewers of Cairo, which hasn't seen an active case since 2004.
With the help of UNICEF and WHO, Pakistan has tried to end the scourge of polio. But it faces a significant obstacle in, among other things, the belief in some areas that the vaccine is harmful or is intended to sterilize children; and that the health workers who administer it can't be trusted.
Such beliefs were exacerbated two years ago when it emerged that a local doctor had set up a fake vaccination drive in the Pakistani city of Abbottabad — infamous now for being Osama bin Laden's hiding place — with the aim of gathering information for the CIA on the al-Qaeda leader's possible whereabouts.
Last summer, Taliban leaders banned vaccinations for all their standard reasons, though some said vaccinations won't be allowed until U.S. drone strikes end.
Then came that week in December.
Monday saw two male workers shot dead. Tuesday: five female workers gunned down and killed. Wednesday: one worker shot in the head and critically wounded.
Later on that final day of the vaccination drive, a female worker and her driver were also murdered on the job.
The health campaign was quickly suspended, threatening the significant progress that had brought levels down significantly in 2012 over 2011.
A new plan
"Some of the people are misusing … the [vaccination] program just for their political and security agenda," Dr. Ezzedine Mohsni, co-ordinator for disease elimination in the WHO Eastern Mediterranean's regional office, said in an interview.
"It's important for the Muslim countries to own the program, to feel that they are responsible for it, and to implement it."
To that end, the clerics meeting in Cairo, from Pakistan, Saudi Arabia and Malaysia among other places, denounced the attacks against health workers (which have also occurred in Nigeria), and called on Muslim parents to vaccinate their kids as a matter of duty.
They now plan on an extensive awareness campaign, and an effort to gather all the related fatwas (religious edicts or rulings) to bolster the case for vaccination.
"We can really do something, but now the question is how fast they are going to move," said Dr. Mohsni.
Al Azhar's grand imam, Ahmad al Tayyeb, seems keen to move fast. He reportedly suggested that specialized doctors travel with Al Azhar clerics in Pakistan to raise awareness and give advice to would-be doubters.
"We will be asked before the almighty God about those who suffer: Why didn't we move to save them?" he reportedly said. "I am moving to the best of my ability."
In this case, his words — and actions — matter. He has significant influence on Sunni Muslims worldwide and, as one Pakistani official who attended the meeting said, the imam's words could change people's lives.
Al Tayyeb also hails from a country that could act as an example to Pakistan.
It has been almost nine years since an Egyptian child was diagnosed with polio, and annual vaccination drives are well attended in this country of more than 80 million.
Still, routine testing of Egypt's sewage system turned up the Pakistani strain of the virus in January, prompting local and UN authorities to organize an extra campaign, just to be safe.
To reach as many people as possible, health officials advertise extensively on television, at factories, schools, churches and mosques.
Officials in Giza even employed a man with a megaphone to roam the streets, to encourage people to come to the campaign that was underway earlier this month.
Tens of thousands answered the call, lining up with their children for the oral vaccine — two drops — that could save their lives.
Of course there are doubters here too, as there are in Western countries, say officials. But on the whole, they feel they have the public's trust.
"There are people who refuse, but we try again, several times," said Dr. Mervat Hammam, the health department official who was overseeing the drive in Giza.
By advertising well in advance, generally "people are satisfied with all the information," she says. "Besides, this isn't our first campaign. We've been doing them since 1998."