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Two shots of a SARS-CoV-2 vaccine may not be enough to protect against infection with the highly contagious Omicron variant.

Why the Omicron variant is raising alarm globally

The Omicron variant of SARS-CoV-2 is spreading faster than any previously detected strain of the virus, with cases confirmed in more than 70 countries including Canada. Preliminary data suggest that Omicron is highly contagious and SARS CoV-2 vaccines may be less protective against infection, but much about the risks posed by the variant remain uncertain.

How transmissible is Omicron?

Early reports from the United Kingdom Health Security Agency suggest that people in close contact with Omicron cases are roughly twice as likely to become infected as those in close contact with Delta cases. Others estimate that Omicron is 25-50% more transmissible than the Delta variant, which in turn was more contagious than the original strain of SARS-CoV-2.

In South Africa, the United Kingdom and other countries with robust testing systems, new Omicron infections have been doubling every two or three days – “a rate we have not seen with any previous variant,” according to WHO Director-General Tedros Adhanom Ghebreyesus. He added that Omicron is probably already circulating in most countries, “even if it hasn’t been detected yet.”

Omicron became the dominant strain of SARS-CoV-2 in South Africa within three weeks of its detection and will likely become the dominant strain in the U.K. this week. The spread of Omicron in Canada lags “a few days, maybe a week behind” the U.K, according to chief public health officer Dr. Theresa Tam.

Does Omicron cause more severe illness?

It’s not clear yet if Omicron will pose greater risks of severe illness and death than other strains of SARS-CoV-2.

Discovery Health, South Africa’s largest private health insurer, claimed in a recent press release that people infected with the Omicron variant had a 26% lower risk of hospitalization than those infected with the Delta strain, but the full details of the analysis haven’t been released yet or peer-reviewed.

The authors only looked at data from the first three weeks of South Africa’s Omicron wave – a period some say is too short to make any conclusions given time lags between infection, hospitalizations, and deaths. Experts have also noted that the findings may be confounded by South Africa’s young population and high rates of past infection – two factors that might reduce individuals’ risk of severe illness from any strain of SARS-CoV-2.

“We have learned by now that we underestimate this virus at our peril,” cautioned Ghebreyesus. “Even if Omicron does cause less severe disease, the sheer number of cases could once again overwhelm unprepared health systems.”

How effective are vaccines against Omicron?

Omicron has a large number of spike protein mutations that may help it partially evade protective antibodies from vaccination or past infection.

Early reports from South Africa and the United Kingdom suggest that COVID-19 vaccines may be less effective against Omicron than the Delta variant. Notably, nearly three in four early Omicron cases in Denmark have been breakthrough infections in people who were fully vaccinated with 2 doses.

Both Astra Zeneca’s and Johnson & Johnson’s SARS-CoV-2 vaccines appear to generate weaker immune responses to Omicron versus earlier strains.

Meanwhile, lab experiments using serum from people who received two shots of Pfizer or Moderna’s mRNA vaccines have shown 25-fold and 50-fold reductions in levels of neutralizing antibody activity against Omicron, respectively.

These findings don’t speak to real-world vaccine effectiveness or other aspects of the immune system, like T cell response, which may offer additional protection against severe illness.

However, both Pfizer and Moderna acknowledged that two doses of their existing SARS-CoV-2 vaccines may no longer provide sufficient protection.

The good news: a third shot of either vaccine effectively made up the lost ground, boosting antibody activity levels back to what they were against other strains of SARS-CoV-2.

Work is also underway on Omicron-specific vaccines – although the United States’ Dr. Anthony Fauci said that variant-specific vaccines may not be necessary depending on the efficacy of boosters.

How are Canadian officials responding?

While existing SARS-CoV-2 vaccines are likely to have some effectiveness against Omicron, particularly for severe disease, WHO’s Director-General warned that “vaccines alone will not get any country out of this crisis.”

“It’s not vaccines instead of masks, distancing, ventilation or hand hygiene. Do it all. Do it consistently,” he explained.

Canadian officials have urged against non-essential travel abroad and banned foreign travellers from entering the country if they’ve recently visited a shortlist of African nations where Omicron may be circulating – a move some experts have criticized as needlessly punitive given the spread of the variant around the globe.

At a first ministers meeting this week, Prime Minister Justin Trudeau and provincial premiers agreed to ensure that as many Canadians as possible, including children, get vaccinated and have access to booster shots.

According to  Trudeau, the federal government has “secured enough booster shots for every Canadian.” The federal government also announced it has sent 85 million COVID-19 tests to provinces and territories and 35 million more are on the way.

Provinces and territories are already rolling out COVID-19 booster shots to select groups.

Ontario announced it will expand eligibility for boosters to anyone over age 18 who received their second dose at least three months ago. Starting Dec. 18, Ontario will also reintroduce capacity limits on indoor entertainment and sports venues.

British Columbia’s Dr. Bonnie Henry urged people to “rethink what you’re doing over the holidays.” The province will soon offer booster shots through pharmacies to people who received their second dose six months ago. According to worst-case scenario modelling, B.C could see 2,000 new SARS-CoV-2 infections per day by the end of the year, up from the seven-day average of 373 as of mid-December.

Alberta has taken a different tack, relaxing restrictions on indoor gatherings ahead of the holidays while making free rapid tests available and expanding booster shot eligibility to those aged 50 and older.

Meanwhile, Quebec is asking people to work from home as much as possible and will provide access to free rapid tests every 30 days.

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