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How does Pfizer’s COVID-19 pill work and who will get it?

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Now that Health Canada has approved Pfizer’s COVID-19 therapeutic Paxlovid for use in people 18 and older, CBC News has been receiving questions about how it works and what its limitations are.

For starters, it’s an oral antiviral treatment. In other words, pills that help you fight off the symptoms of COVID-19.

But here’s a closer look at the ins and outs of the treatment.

How does it work?

Paxlovid consists of two antiviral drugs packaged together: nirmatrelvir and ritonavir. 

Patients take three pills twice a day: two of nirmatrelvir and one of ritonavir. In total, the full course of treatment requires you take 30 pills over the span of five days.

Nirmatrelvir is a new drug developed by Pfizer-BioNTech, while ritonavir is an existing drug often used in the treatment of HIV/AIDS.

The two drugs work together, health experts say. Nirmatrelvir does the heavy lifting by hacking the virus’s ability to replicate and multiply, while ritonavir acts as a sidekick to nirmatrelvir, enabling it to remain in the body longer. 

Paxlovid is something called a protease inhibitor, explained Dr. Isaac Bogoch, an infectious diseases specialist at Toronto General Hospital.

“It stops the virus from dividing by blocking a part of its life cycle,” he said, noting this allows your immune system to fight off the virus a lot easier.

But it’s crucial to start treatment soon after infection, Bogoch said, “to really nip it in the bud early.” 

According to immunologist Dr. David Burt, who is also a member of Toronto’s Black Scientists’ Task Force on Vaccine Equity, the only drawback with these types of treatments is a “very narrow window of opportunity” before the drug loses its effectiveness.

When taken within five days of infection, Pfizer’s clinical trials showed that the drug reduced risk of hospitalization or death by 85 per cent.

Who will have access to Paxlovid? 

Canadians will need a prescription to get Paxlovid, according to Health Canada.

The Public Health Agency of Canada (PHAC) has been working with a group of clinical experts to determine how to best distribute Paxlovid and give it to the country’s most-vulnerable populations. 

Dr. Howard Njoo, Canada’s deputy chief public health officer, says people who are immunocompromised, 80 years of age and over, or who may not have access to health care because of geographical or socioeconomic concerns are first in line — regardless of vaccination status.

He did caution, however, that the early limited supply of the drug may complicate things. 

Health Canada’s Chief Medical Adviser Dr. Supriya Sharma agreed, saying global supply of the drug is still tight and Canada is competing with other countries to get more Paxlovid treatments. 

“We have a small quantity for Canada to begin with, but we will, over the next few months, be getting much more,” she said.

WATCH | How might patients access the COVID-19 antiviral pill?

how does pfizers covid 19 pill work and who will get it

How might patients access the COVID-19 antiviral pill?

6 days ago

Duration 4:09

Infectious diseases specialists Dr. Susy Hota and Dr. Isaac Bogoch talk about how people might be able to access the new COVID-19 antiviral pill, Paxlovid, and how it could impact the health-care system. 4:09

It is important to note that patients seeking the treatment will also need to secure a positive PCR test to confirm they have COVID-19. But in the wake of the latest Omicron wave, lab-testing capabilities have been limited in many parts of the country — meaning just getting a test could pose its own set of challenges. 

If a PCR test is not available, Chief Public Health Officer Dr. Theresa Tam said a positive result on a rapid antigen test would also suffice.

Because the drug should be taken early on in the course of your illness — within five days of symptom onset — you are on the clock to get both a positive lab test and the prescription in hand.

How much do I have to pay for a course of Paxlovid?

If you do qualify for a Paxlovid prescription, it won’t cost you anything out of pocket. The federal government will take care of the bill. 

“We’re providing those medications to the provinces and territories free of charge. So there’s no cost to the individual, there’s no cost to the province and territory,” Sharma said.

When will it be available?

There is no exact date when Paxlovid will be widely available to the public, though Canada has already purchased one million doses. 

The first batch, consisting of 30,000 sets of pills, is already being distributed and more than 120,000 additional treatments are expected by March, Health Minister Jean-Yves Duclos has said.

WATCH | Paxlovid shows great promise despite logistical hurdles, Bogoch says: 

how does pfizers covid 19 pill work and who will get it 1

Pfizer’s new COVID-19 antiviral pill ‘big step forward,’ says specialist

8 days ago

Duration 3:04

Paxlovid, Pfizer’s pill to treat COVID-19, shows great promise despite some logistical hurdles to get the drug to those who need it, says infectious disease specialist Dr. Isaac Bogoch. 3:04

“The provinces will essentially get the same amount of drugs per capita — but it’s not going to be very much,” said Bogoch. “Basically you’ll get a proportional amount of drugs to your population.”

This initial amount will fall short of what’s needed, said Bogoch. However, he emphasized that what is received will be put to good use fairly quickly.

“I think it’s going to be several months away before we actually have a lot more of this drug around,” he said.

Is Paxlovid a replacement for vaccines?

Absolutely not, experts say.

According to Dr. Lisa Barrett, ​​an infectious disease specialist based out of Dalhousie University in Halifax, “the best thing you can do for your health is to reduce your chances of getting infected in the first place.”

That means Paxlovid is not a replacement for COVID-19 vaccines, she said. Instead, it is to be used in addition to vaccines. Specialists say it functions as an added layer of protection to combat the coronavirus.

“Vaccines remain the fundamental and critical way we prevent infection from going through a community,” said Kevin Mohamed, a spokesperson for Pfizer Canada.

​There are key fundamental differences in how vaccines and antiviral pills target the virus.

Unlike the vaccines, Paxlovid doesn’t target the spike protein, which can mutate. Instead, it attacks the virus’s ability to spread, meaning the treatment should help fight the virus, regardless of the variant.

One thing Paxlovid does have in common with vaccines is that they share some of the same goals: Reducing the rate of COVID-19 hospitalizations and deaths.

Is it effective against Omicron?

Early data suggests Paxlovid is effective against the Omicron variant. 

Three separate lab studies released by Pfizer Inc. found that nirmatrelvir — the part of Paxlovid that stops the virus from multiplying — maintains its antiviral activity against COVID-19 variants, including Omicron.

You can read those lab studies here, here and here.

Mohamed said while this research is “very, very promising,” the company is continuing to test and evaluate how effective the treatment is against variants of concern.

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