Poor early efficacy of Pfizer’s first coronavirus vaccine does not refute Canada’s dosing strategy: study author – fr

A dose of Pfizer coronavirus vaccine only 30% effective in preventing infection with variant B.1.1.7: study – fr

The author of a new study that casts doubt on the early effectiveness of the Pfizer-BioNech coronavirus vaccine against variants of concerns says he believes the data is not applicable to the situation in Canada where the doses are spaced four months apart.

Following the results of nearly 40,000 people tested for COVID-19 in Qatar, the study published Wednesday evening in the New England Journal of Medicine found that a single Pfizer jab was effective for only 29, 5% to prevent infections, asymptomatic or otherwise.

One injection of Pfizer was found to be 54.5% effective in preventing “serious, critical or fatal” outcomes from infection with variant B.1.1.7, which is now prevalent in Ontario.

But author Dr Laith Jamal Abu-Raddad told CP24 on Thursday that Qatari health officials followed Pfizer’s dosage guidelines, giving second doses no more than 21 days after the first in most cases. case.

“The dose estimate we have provided is strictly effectiveness within the first three weeks immediately after the first dose and should not be interpreted to mean final effectiveness after three or more weeks from the first dose.” , did he declare. “We couldn’t determine the latter exactly because in our population everyone received the second dose three weeks after the first dose.”

Following the monograph means that many of the infections found in the study occurred soon after subjects received their first doses, and not two weeks later and beyond when immunity is expected to increase as a result of the treatment. ‘injection.

“The one-dose figures in our article show that immunity has developed after the first dose, but it has not yet reached its final level.”

Among those who received both doses, the study found that vaccine efficacy against B.1.1.7 infection, with or without symptoms, was 87%, increasing to 90% 14 days after the second dose.

It was 100% effective against severe symptoms or death.

“In Qatar, as of March 31, rupture infections were recorded in 6,689 people who received one dose of the vaccine and in 1,616 people who received two doses,” wrote the study authors. “Seven deaths from Covid-19 were also recorded among those vaccinated: five after the first dose and two after the second dose.”

It is assumed that many of these infections occurred in the first few days after subjects received their first injection, meaning that antibody levels did not have time to build up in the body.

The Qatar study appeared to find less efficacy and used a larger sample size than most studies and datasets used by the National Advisory Committee on Immunization (NACI) to justify its initial recommendation of ” spacing out the dosage by 16 weeks.

Other studies cited by NACI found that a single dose of a coronavirus vaccine was 65-80% effective in preventing a serious outcome.

NACI cited the UK example, but doses were often only spaced 12 weeks apart. The World Health Organization (WHO) itself has recommended a maximum separation of six weeks, but only in critical circumstances.

Ontario officials have suggested that the gap between the first and second dose could be narrowed soon if supply increases continue, but no firm policy changes have been made.

And a Ford government minister cited the study as a reason to question the NACI dosing schedule and the continued transmission of COVID-19 variant cases through points of entry.

“One dose of Pfizer is potentially 30% effective against UK variants, this is a study conducted in Qatar, so what we are asking the federal government to do here is to support us.” Associate Minister of Small Businesses Prabmeet Sakaria told reporters on Thursday.

Speaking about the study Thursday, Deputy Chief Medical Officer of Health Dr. Barbara Yaffe said Ontario has had excellent results with the single-dose regimen, with 70% effectiveness against overall infection and more than 90% effective against severe outcomes. .

“We know it takes time to respond to the vaccine, 14 days and more in the elderly,” she said.

“The experience in Ontario has been very good. “

Chief Coroner Dr Dirk Huyer added that the province experienced good levels of immunity from 14 days after the injection, rising steadily until 28 days after the vaccine.

Pfizer corporate affairs director Christina Antoniou told CP24 their position remains that vaccine doses should be given 21 days apart for maximum effectiveness.

“We have no data from Pfizer regarding a single dose approach and our current research is specific to two doses 21 days apart. Our position has not changed and the statement we issued on March 23 remains valid. “

Although three other vaccines are approved for use in Canada, Pfizer-BioNTech remains the most widely deployed vaccine in Ontario.

Using data from the first 3.5 million doses administered in Ontario between December 2020 and April 2021, epidemiologist Dr Zain Chagla said the current spaced dosing strategy has been extremely effective.

From the start of Canada’s vaccination campaign in mid-December 2020 until the end of April 2021, nearly 6,800 people have been infected with COVID-19 after receiving a dose of a vaccine.

“Of these, 4,515 cases were reported within 14 days of their first dose of vaccine and 2,274 cases were reported at a minimum of 14 days,” a Health Canada spokesperson told CP24 Weekly. last.

UHN infectious disease specialist Dr Isaac Bogoch said a first dose is always better than no dose.

“You get quite a bit of protection after the first few doses of infection – the other big point is that we just aren’t seeing proportionally that many people who got a first dose entering the hospital. “

Qatar’s experience shows similarities to that of Ontario, although the province eclipses Qatar in terms of population.

Qatar saw the B.1.1.7 and B.1.351 variants become dominant over earlier ‘wild-type’ COVIDs at around the same time in mid-March.

For the B.1.351 variant first discovered in South Africa, the study saw even poorer results with a single dose.

The study found that one dose of Pfizer-BioNTech vaccine was only 17% effective in preventing infection with B.1.351.

It has been shown to be zero percent effective in preventing hospitalization or death from B.1.351.

The B.1.351 variant is detected only sporadically in Ontario, with only 246 examples detected in the last month.


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