"Stop. Are you sick?"

That's the sign on the front door of Kelly O'Dwyer-Manuel's Peterborough, Ont., home.

She's trying to protect her infant son from a dreaded virus that circulates every winter. It's called respiratory syncytial virus (RSV), and this has been the worst RSV season in six years.

RSV is the most common cause of pneumonia and bronchitis in infants, although it causes only mild cold symptoms in most healthy people.

"I'm on edge and will remain on edge until the summer," said O'Dwyer-Manuel, who keeps 14-month-old Charlie indoors as much as possible.

She says she's in touch with other nervous mothers in the same situation.

"People are terrified, quite frankly."

Those anxious mothers are caught in a paradox.

There is a drug that can help protect their premature infants from severe RSV infection. The provinces will pay for it, but it's so expensive that access is tightly controlled.

Every province has a set of criteria to determine which infants qualify for the drug.

And every winter, there are babies who don't qualify.

The highly contagious RSV virus can be extremely dangerous to some infants, but getting a specialized drug to protect them is prohibitively expensive 3:23

1 in 12 babies born premature

One out of every 12 babies born in Canada every year is premature and might be a candidate for RSV protection.

The drug is called Synagis (palivizumab) and it costs between $5,000 and $9,000 per infant per year — still as expensive as when it first became available almost 20 years ago.

Why does it cost so much? It's difficult to get an answer. The medical experts we asked said they didn't know, and the drug companies refused to say.

Across Canada last year the provinces collectively spent about $43 million to protect fewer than 7,000 preemies.

Synagis provides antibodies to help boost a newborn's immune system so it can fight the viral infection. The drug is given in a series of four or five monthly injections, throughout the RSV season.

The drug was available through special access in 1998, then approved in Canada in 2002. It is marketed by U.S.-based AbbVie.

AbbVie declined a request for an interview to discuss the price of the drug.

In an email to CBC News, AbbVie's spokesperson said there are "numerous factors that contribute to the retail price," including "R&D and manufacturing costs and product distribution."

When pressed for more information, the company referred us to the drug's maker, AstraZeneca/MedImmune. At the time of publication, the company had not responded to our questions about the price.

Risk of conflict of interest

Some experts challenge the idea that manufacturing costs are keeping the price high.

Pharmaceutical specialists with the World Health Organization have investigated and concluded that the cost of manufacturing the drug is relatively inexpensive.

"The cost actually to develop a single gram of antibody is a known price, and it's estimated to be between $100 and $130 US per gram," said Robin Sparrow at the WHO's Technology Transfer Initiative in Geneva. She said her group believes it will be able to produce a full treatment of Synagis for $250 US.

Kelly O'Dwyer Manuel holds her son Charlie, whose compromised immune system makes him more susceptible to respiratory syncytial virus. (CBC)

In Canada, the drug sells for $15,000 per gram. It's distributed in 50 mg and 100 mg vials, and the amount required depends on the weight of the baby.

"You should be able to produce it for $100 to $200 per treatment," said Prof. Han van den Bosch of the Utrecht Centre for Affordable Biotherapeutics in the Netherlands.

A Manitoba doctor who's responsible for deciding which babies in his province get the drug says the criteria vary from province to province.

Every year it is controversial when we talk about a product that is only given to a select group of patients. - Dr. Aaron Chiu

"Every year it is controversial when we talk about a product that is only given to a select group of patients,"said Dr. Aaron Chiu.

Adding to the controversy is AbbVie's active role in distributing the product through patient education campaigns and handling the administrative paperwork in some provinces.

Chiu said Manitoba designed its program to be independent of the drug company. "We don't accept any funding from Abbvie," he said.

But AbbVie does give money to some hospitals in Canada.

"We do support general RSV education through an immunoprophylaxis program in which we provide support to 43 different programs, mainly hospitals, across the country," AbbVie said in an email. "The programs that receive these grants determine for themselves how they employ the funding."

The Canadian Paediatric Society (CPS) has expressed concern about the risk of conflict of interest because some doctors involved in administering the Synagis program also receive research funding from AbbVie.

"I find it very disturbing and have for a very long time," said Dr. Joan Robinson, chair of CPS's infectious diseases and immunization committee.

In 2015, CPS published a position statement on Synagis that makes it clear doctors involved in manufacturer-funded research should not be involved in deciding who gets the drug.

In Manitoba, Dr. Aaron Chiu is responsible for deciding which babies get the drug. (CBC)

Chiu says the CPS statement makes a valid point, but it's difficult to be completely independent from AbbVie, the sole distributor of Synagis in Canada.

"I have regular contact with the company, from product manager to regional representative, to discuss shipment issues, cold-chain breaks, invoices, etc.," he said.

He said he's also given talks on behalf of the company in the past.

'Aggressive' sales tactics

Dr. Kim Barker, the medical officer of health for Nunavut, says AbbVie is "absolutely aggressive" with its sales tactics, emailing and calling "constantly."

"It's the only pharmaceutical company I've ever had contact with up in Nunavut. I haven't had any others contact me," Barker said.

"We've got one of the highest RSV rates, so they see us a good candidate to maintain the purchasing of the product," she said, adding that company sales representatives fly to the territory at least once a season.

(Natalie Holdway/CBC)

Barker believes AbbVie is trying to encourage Nunavut to give the drug to more babies.

"It's largely driven by them trying to convince us that we're not providing appropriate care to Nunavummiut infants, and trying to convince us of the need, and some of the potential areas of benefit, if we were to make it universal."

In an email, AbbVie said, "We work with all Canadian provinces and territories based on their own self-determined eligibility criteria for utilization. We abide by the Innovative Medicines Canada code of business conduct."

Can be purchased privately

In Ontario, AbbVie is directly involved in running the Synagis program, under the province's public drug programs.

AbbVie processes all the enrolment forms and informs family doctors which infants qualify and which ones are rejected, Health Ministry spokesperson David Jensen said in an email.

Although the cost of Synagis is out of reach for many families, the drug is available for private purchase. McKesson Specialty Pharmacy, which has locations across Canada, can fill the prescription. It's not clear how many families try to buy the drug themselves. McKesson wouldn't disclose sales numbers, or the price it charges for the drug.

"We are bound by contractual rules with the manufacturer," McKesson said in an email. "The sales data belongs to the manufacturer and therefore McKesson Canada can't provide you with this information."

In an email to CBC News, AbbVie's spokesperson said private sales are about 0.1 per cent of total Canadian sales — figures that are "not public information."

Dr. Kim Barker, Nunavut's medical officer of health, says AbbVie is 'aggressive' in marketing Synagis to the territory. (Sima Sahar Zerehi/CBC)

Several companies have new drugs for RSV in the development pipeline. Once they are on the market, many believe competition will lower the cost of protecting premature infants from RSV infection.

"You can't blame the company for trying to make as much profit as they can before a better product comes along," said Robinson. She added that there is disagreement about how widely used the drug would be if the cost was lower.

"It's not as though there are a whole bunch of kids out there who would really benefit substantially who are not getting it," she said.

Experts also urge parents to wash hands and use other standard measures to avoid spreading illness during RSV season.

In the meantime, O'Dwyer-Manual won't relax until summer.

"I don't think I can express in words how terrifying it would be for him to go back into hospital," she said, wiping her eyes with a tissue.

RSV: Respiratory syncytial virus (RSV) sends more infants and toddlers to hospital than any other bug. And the virus causes 200,000 deaths in toddlers and infants around the world every year, according to the World Health Organization. It's especially dangerous to premature infants and babies with heart and lung conditions. Everyone in the world is eventually infected with RSV, experts say, but most people don't notice because the virus causes only mild cold symptoms in healthy people.

ABBVIE SALES FIGURES: According to AbbVie's 2016 annual report to shareholders, international sales (net revenues) of Synagis were $730 million in 2016. AbbVie's total net revenues from drug sales in Canada were $624 million. Synagis is one of 19 AbbVie drugs approved in the Canadian market.