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4th dose eligibility expands Earlier this week, the National Advisory Committee on Immunization (NACI) recommended that people over 80 and those living in long-term care settings be prioritized for a second booster dose of the COVID-19 vaccine as cases rise across the country. Swiftly after NACI’s announcement Tuesday, provinces began unveiling their fourth dose rollout plans — some of which differed from the federal recommendations. In Ontario, anyone 60 and older at a recommended interval of five months after the initial booster shot can receive an additional booster. Meanwhile, in B.C., the province is making a fourth dose available to seniors, starting with residents of long-term care and assisted-living homes. People over age 70 in the community, Indigenous people 55 and up and those who are extremely vulnerable will also be included in the vaccination campaign this spring. Starting next week in Alberta, fourth doses will be available to all seniors in congregate care, those who are 70 and older and Indigenous people 65 and older. Find out who is eligible for a fourth dose in all provinces and territories here. 
Do rapid tests still work against the latest variants? As cases surge during the sixth wave of the COVID-19 pandemic, some may be noticing they have symptoms but a rapid antigen test shows a negative result. Does that mean the rapid antigen tests are less effective at detecting Omicron and its subvariant BA.2 than previous strains? Experts say people can still test negative on a rapid test in the first few days they have symptoms, partly because of how quickly vaccination clears the amount of the virus in an infected person's body. "If the antigen test is dependent on the amount of virus in your upper respiratory tract, you will still be infectious … in the first few days," said Dr. Earl Rubin, an infectious disease specialist at the Montreal Children's Hospital. "But you may clear the virus more rapidly if you have good antibody from the vaccine … and therefore the antigen test may become negative quicker in those who are vaccinated rather than the unvaccinated." The Ontario COVID-19 Science Advisory Table in February published findings from an analysis of preprint studies suggesting that the pooled sensitivity of rapid antigen tests for detecting Omicron infections is about 37 per cent, compared with 81 per cent for the Delta variant. On its website, Health Canada says it has "no evidence" that variants affect the ability of the tests to confirm COVID-19 cases, but notes these new testing devices are still being investigated. Read more on the effectiveness of rapid tests from Global News reporter Aya Al-Hakim here. 
Q: Why isn’t the definition of ‘fully vaccinated’ a moving target? Are people really adequately protected with just two shots rather than two plus a booster at this point? “The definition of fully vaccinated is undergoing reviews by several vaccination panels around the world, including NACI here in Canada,” says Gerald Evans, an infectious disease specialist at Queen's University in Kingston, Ont. “It is apparent since Omicron arose that three doses of vaccine in most healthy adults and adolescents hits a ‘sweet spot’ when it comes to both protective (immunity from severe infection) and sterilizing immunity (immunity from infection) to COVID-19.” Evans said two shots of the vaccine looked sufficient for the Alpha and Delta variants, but with Omicron, three doses appears to “substantially boost” immunity from infection and protect recipients from severe infection at the same level two doses did with the previous variants. Some health experts, like Dr. Samir Sinha, director of geriatrics at Sinai Health and University Health Network hospitals in Toronto, are calling for the definition of fully vaccinated to change. "I think we really need to start getting rid of this term 'fully vaccinated' as meaning just two doses," he said. "It's time we start revising our language." Sinha says part of the problem with this definition is it still includes two doses when older adults are now recommended to get four. Even though more than 81 per cent of the Canadian population has received two doses of a COVID-19 vaccine, uptake of a third dose has been slow — currently at 47 per cent. | 
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