Tipping point: Collective immunity

It’s hard to see the good and the good in the wave that is currently sweeping over Quebec and the rest of the world. However, a glance in the rearview mirror reminds us that one of the winning bets for Quebec, in 2021, will have been to go against the tide by offering a first vaccine to the greatest number of people and by extending the gap between each dose. By walking on the thin thread of collective immunity, Quebec has scored points.

Faced with all the unknown in which COVID-19 has plunged the scientific world, and even more the Omicron variant, establishing public health policies has become an extreme sport. You could say that the D^r Gaston De Serres, member of the Quebec Immunization Committee (CIQ), is a past master in this high-flying sport, by convincing, at the turn of the year 2020, the Quebec government to do the opposite of what were preparing to do most of the countries of the world.

As the wealthiest states on the planet, including Canada, scrambled for the first available doses of vaccine, manufacturers were pressing to put second doses in reserve for the first vaccinated in order to make a second injection 21 or 28 days later.

The United States and Canada followed suit. But in December 2020, with more than 2,000 cases identified per day, the escalation of infections in Quebec foreshadowed a new deadly wave, with a health network already on its knees.

To slow down the transmission of the virus, the CIQ then urges the authorities to use the doses that drop in at the beginning of January to vaccinate the greatest number of vulnerable people, in particular the elderly living in CHSLDs and RPAs. Quebec has still not recovered from the massacre that occurred in the spring of 2020 in CHSLDs.

“We were swimming against the tide, we were going completely against Big Pharma. I remember discussing it at the time with the D^r From Serres. I was far from being sure of his strategy. And it was he who convinced me. It was our only weapon to limit in the short term the number of serious cases and hospitalizations, ”recalls Benoît Mâsse, epidemiologist at the School of Public Health of the University of Montreal.

In contact with epidemiologists from the prestigious epidemiology team at Imperial College London, Benoit Mâsse notes that his British colleagues are making the same calculation. “There was such a surge in cases, and so few doses. If we had two elderly parents, which one would we vaccinate? Scarcity forced us to make this choice, ”he says.

The first echoes from the United Kingdom, already drowned in a deadly wave due to the Alpha variant, confirmed the Quebec experts in their choice, explains D^rGaston De Serres. Contrary to the manufacturer’s claims, which guaranteed about 50% protection 24 hours after the first dose was given, initial studies observe up to 90% protection with the Pfizer-BioNTech vaccine, no less than two weeks after the first dose. first dose. The most bereaved country in Europe will be the first to move forward in December 2020, relying on the granting of a single dose to the greatest number, to limit the wave that has been sweeping since September.

“There was a big political stake in going in the opposite direction of the United States and the whole world. But from December 15, we also chose to vaccinate as many people as possible, ”says Dr.^r From Serres.

The National Advisory Committee on Immunization (NACI) of Canada then kicked in the shackles, not keen on the idea, no one knowing at that time how long the 90% immunity offered by a single dose of vaccine would last.

The D^r Jesse Papenburg, respiratory infection expert at the Montreal Children’s Hospital of the McGill University Health Center (MUHC) and member of the NACI, says this decision, then endorsed by several countries, saved lives. “At first, Pfizer even threatened to cut off food in Canada. Analysis of D^r However, De Serres clearly demonstrated the strong protection after a single dose, ”he explains.

The race started in January 2021 to vaccinate as many people as possible in Quebec did not stop the second wave which fell forcefully in January, February and March. But the expanded access made it possible to limit the damage of the following wave, fueled by the arrival of the Delta variant in the spring of 2021.

The numbers say it all: the first wave of March 2020 killed more than 5,200 people over 70, the second (August 2020 to March 2021), 4,489. The third (March 21 to July 2021) was resulting in 443 deaths and thousands fewer hospitalizations.

A double hit

Making the vaccine accessible to several age groups meant stretching the time between the two doses as much as possible. Extended to 16 weeks in March by Quebec, this deadline was far from the 4 or 8 weeks recommended at the start. But this imposed figure has proved to be a double winner for Quebec, several studies having shown that spreading out doses ultimately conferred prolonged immunity on those vaccinated. “This decision not only saved lives, but the extended interval probably continues to help us, as several people received their second dose only a few months ago,” insists Dr.^r Papenberg.

In a prepublication study, subsequently published by the New England Journal of Medicine and cited by the New York Times, data collected by D^r De Serres showed in September that the 16-week gap between doses had generated an immune response as optimal as a real infection, followed by a vaccine. Several countries in need of doses, such as Singapore and India, will adopt this winning approach in spring 2021 to juggle the tsunami of infections caused by the Delta variant.

Again this fall, field data revealed that vaccines received in Quebec continued, even after 32 weeks (8 months), to offer barely impaired protection against serious infections. “We still have almost the same protection against hospitalizations. But the protection against infections, it fell from 92% to 77% for 18 to 49 years and to 63% in people over 70 years ”, explains D^r Gaston De Serres.

That was before the arrival of Omicron, who came to overturn all certainties regarding the remaining immunity conferred by a previously perfect vaccination schedule. Quebec had bet in November on the rapid vaccination of children to stifle the fourth wave and was still betting on the spreading of the third dose to surf on collective immunity. “By vaccinating children, we cut the transmission of many from their parents, 20 to 40 years,” said Gaston De Serres.

However, with Omicron, the winning bet of the delayed vaccines in the second wave is shattered for the third dose. Israel (in July), the United Kingdom, France, the United States (in September) and many countries, which quickly injected booster doses to resist the rise in cases this fall, now appear to be better armed than the Quebec to face Omicron.

Now fit the D^r From Serres, getting a third dose as quickly as possible is essential. But, Omicron or not, continuing to reach the unvaccinated will be just as much to avoid the congestion of the health network. “If we succeeded in reaching the 600,000 people still unvaccinated, that would change everything. We would do even more mileage than by limiting ourselves to the third doses, because it is the vaccinated people who are still most often hospitalized, ”he said.

Many unknowns remain as to the dangerousness of Omicron. It remains to be seen how the remaining immunity of the “extended lead time” dual vaccine will negotiate with the day variant. To get through this latest twist of SARS-CoV-2, it will once again be necessary to find the balance on the tenuous thread of collective immunity.

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