4th COVID-19 vaccine dose: What’s the science behind another booster? – National | Globalnews.ca

Patricia Flemming says she is feeling more motivated and less fearful of catching COVID-19 after getting her booster shots.

The 71-year-old is among the 87 residents at Chester Village to have received a fourth COVID-19 vaccine dose since Dec. 30 at the Toronto nursing home.

“The third one, I noticed a bit of fatigue,” said Flemming, who is a retired nurse from Nova Scotia.

“This one had a little more fatigue associated with it. But other than that, there [were] no real issues.”

Chester Village was one of the first long-term care homes in Ontario to fully vaccinate almost all of its residents against the coronavirus last January. And now a year later, the not-for-profit facility is offering all eligible residents the Moderna vaccine as a fourth dose.

As the highly transmissible Omicron variant of COVID-19 surges across the country, Canada’s National Advisory Committee on Immunization (NACI) has recommended that moderately or severely immunocompromised Canadians may receive a second booster or fourth shot at least six months after their last dose.

“Many of these individuals are at a higher risk of severe outcomes of COVID-19 and also at increased risk of decreasing protection over time since vaccination,” NACI said in its updated guidance released on Dec. 3.

Besides long-term care homes, the Ontario government is making fourth doses available to residents of the province’s retirement homes, elder care lodges and other congregate settings.

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Meanwhile, Manitoba is recommending a fourth dose for “moderately to severely immunocompromised individuals” at least six months after the last received dose.

Saskatchewan has also opened up fourth doses to people who are immunocompromised, provided it has been three months since their third dose.

According to NACI, the intent of a booster dose is to restore protection that may have decreased over time or is no longer sufficient in individuals who initially responded adequately to a complete primary vaccine series.

The World Health Organization (WHO) has repeatedly warned against “blanket booster programmes”, stressing greater equity globally in the distribution of and access to vaccines.

The agency says more people worldwide should be vaccinated with first doses before others receive boosters.

“Booster after booster in a small number of countries will not end a pandemic while billions remain completely unprotected,” said Tedros Adhanom Ghebreyesus, WHO’s director-general, during a news conference on Jan. 6.

But Canada, like several other countries, is pressing ahead with boosting its population amid a surge in infections thanks to the Omicron variant.

A growing body of research shows that a first booster or third COVID-19 vaccine dose, which is recommended for all Canadian adults, raises antibody levels, cuts death rates and hospitalization.

But there is limited data to back the need for a fourth dose or additional subsequent doses, experts say.

“It is, in my view, somewhat early to start thinking of a fourth dose when the third dose itself hasn’t been fully deployed in our population,” said Dr. Ciriaco Piccirillo, an immunologist and senior scientist at the Research Institute of McGill University Health Centre (MUHC).

As of Sunday, 9,810,166 people or roughly 25 per cent of the Canadian population had received a third COVID-19 vaccine dose, according to covid19tracker.ca.

Piccirillo believes a two-dose or triple-dose vaccine series should be “more than sufficient” for people who don’t have pre-existing conditions and who have normal immune systems.

However, subsequent boosters are “likely very important” for the elderly, immunocompromised individuals and cancer patients, he added.

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Israel, which is now administering fourth doses of the Pfizer/BioNTech vaccine to people over 60, health workers and immunocompromised patients, has played a leading role in studying the effects of COVID-19 vaccines.

The country was the fastest to roll out two-dose inoculations to a wide population a year ago and one of the first to give third shots as boosters.

Citing preliminary findings of an Israeli study, Prime Minister Naftali Bennett said on Jan. 4, that a fourth dose of COVID-19 vaccine boosts antibodies five-fold a week after the shot is administered.

Like Canada, the U.S. Centers for Disease Control and Prevention (CDC) has recommended a fourth shot for anyone who is moderately and severely immunocompromised.

But in the U.K., the Joint Committee on Vaccination and Immunization has advised the government that there was no need to offer a fourth dose, or second booster, to vulnerable people at this time. It cited data that shows a third shot offers lasting protection against admission to the hospital three months after the dose.

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The purpose of giving a booster is to raise the level of neutralizing antibodies from a vaccine, especially in immunosuppressed individuals, who have difficulty producing antibodies due to a weakened immune system, said Dr. Horacio Bach, an infectious diseases expert at the University of British Columbia.

However, more research is needed to see the impact of a fourth shot before it can be rolled out to the general population, he said.

Dr. Samir Sinha, director of geriatrics at Sinai Health and University Health Network hospitals in Toronto, said while a fourth shot may provide benefit in certain vulnerable populations who are at risk of waning immunity, it still remains to be seen if a mass rollout among the general population is needed going forward.

“This might become one of those illnesses that we need a booster on an annual basis, for example,” he said.

“But right now, we just don’t have that information on whether a fourth shot would truly be beneficial for younger, healthier populations.”

The current booster shots have exactly the same formula as the first two doses.

For now, each dose is targeting the same S protein of the original Wuhan strain of SARS-CoV-2, Piccirillo said. The S protein is the key that the virus uses to dock into cell receptors to enter human cells, causing infection.

Early findings about a single booster in the context of the Omicron variant are promising.

Citing data from the U.S. National Institute of Allergy and Infectious Diseases (NIAID), the United States’ top doctor, Anthony Fauci, has said that the current “booster vaccine regimens work against Omicron,” whether your dose is Pfizer or Moderna.

Research from the University of California indicates boosters can push protection against Omicron back up to roughly 48 per cent. As for preventing severe disease, boosters appear to push that efficacy back up to 91 per cent.

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A study released in the United Kingdom also found a COVID-19 booster shot can provide 71 to 75 per cent protection against mild symptoms of COVID-19.

Meanwhile, both Pfizer and Moderna, are working to develop booster shots that can specifically target the Omicron variant.

This week, Moderna’s chief executive Stephane Bancel said that the efficacy of boosters against COVID-19 is likely to decline over the next few months and people may need another shot in the fall of 2022.

“I  suspect that in … the upcoming months, we will be seeing commercially available booster shots that are variant specific,” Piccirillo said.

Sinha agrees. “There might be a future booster dose that’s tailored more to variants like Omicron or other future variants. But that takes time to develop.”

For now, James Patridge, 76, is looking forward to getting his fourth shot at Chester Village next week so he can move around more freely and “live longer.”

“It protects me from the virus,” he said, urging others to get vaccinated.

— with files from Reuters

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