Safe to Get Same Vaccine Again?
As some experts go along to warn of very rare side effects associated with the AstraZeneca vaccine, Canadian health officials are now reviewing the research on mixing various COVID-19 shots. A report of a "mismatched" vaccine regimen is underway in the U.Yard. — but some scientists say there's reason to believe that administering two doses of unlike products could boost a person's immune response beyond what tin be achieved by giving the aforementioned shot twice. The National Advisory Commission on Immunization (NACI) caused some confusion earlier this calendar month when it said the viral vector shot from AstraZeneca is not the "preferred" product given its associated risk of vaccine-induced immune thrombotic thrombocytopenia (VITT) — a status that causes claret clots. That warning came out after hundreds of thousands of Canadians had received the AstraZeneca vaccine already. According to the Ontario Science Table, estimates of the frequency of VITT in individuals who take received the AstraZeneca vaccine now range from 1 example in 26,000 to 1 case in 127,000 doses administered. The risk of developing this side effect, combined with an uncertain delivery schedule for time to come supply, has prompted some provinces to consider pausing AstraZeneca vaccinations altogether. Dr. Brent Roussin, Manitoba's primary provincial public health officer, said Sunday a temporary suspension "has been discussed at many levels, and certainly discussed at our provincial program right now." Christine Elliott, Ontario'due south health government minister, said Monday that recipients of the AstraZeneca vaccine may receive a dissimilar shot for their second dose. While the AstraZeneca production has been accounted safe and effective repeatedly by Wellness Canada regulators, some people who already accept received that vaccine are now looking at their options. Researchers at Oxford University in the U.Chiliad. launched a study in early February to explore the possible benefits of alternate different COVID-19 vaccines. According to the atomic number 82 scientists, the study is "looking for clues as to how to increase the latitude of protection against new virus strains." The report — otherwise known as the COVID-19 Heterologous Prime Heave report, or "Com-COV" — is collecting information to determine whether receiving two different types of vaccine generates an immune response at least equal to the response that follows receiving the same product twice. (A "heterologous" vaccination regimen is one that uses more than one product.) Some early results may be available soon; the written report team told CBC News information technology'south "anticipating sharing information in the next calendar week or so." All of the shots currently in employ in Canada and the U.K. follow the same two-dose schedule, with a "prime" dose followed by a 2nd "heave" dose some weeks later. (The one-dose Johnson & Johnson shot has been approved for use in Canada but information technology has not yet been administered.) The Oxford researchers are evaluating the effects of vaccine combinations — comparing the results of a outset dose of the AstraZeneca vaccine followed by either the Pfizer vaccine or a second AstraZeneca dose, or a first dose of the Pfizer vaccine followed past either the AstraZeneca or a second dose of the Pfizer. A second study, called Com-COV 2, includes the products from Moderna and Novavax as booster vaccines. Jonathan Van-Tam is the deputy chief medical officer for England and one of the senior officials responsible for this study. He said this research will "give us greater insight into how we tin can use vaccines to stay on elevation of this nasty illness." "It is possible that by combining vaccines, the immune response could be enhanced, giving fifty-fifty higher antibody levels that last longer," he said in a statement. "Unless this is evaluated in a clinical trial, we but won't know." Dr. Helen Fletcher is a professor of immunology at the London School of Hygiene and Tropical Medicine in the U.K. She said a "mismatched" vaccine programme would deliver some applied benefits — vaccine delivery logistics would be greatly simplified — but in that location could be another adept reason to pursue a mixed-dose regimen. "I'm excited about the written report because I think it'south likely that the immune response will be even meliorate if you mix and match vaccines," Fletcher said in an interview with CBC News. "Mixing vaccines could give you a stronger immune response, or information technology could give a broader type of allowed response — generating a wider range of antibodies, or T cells besides as antibodies. It'due south also possible that a mix and lucifer regimen could strengthen our allowed response against virus variants considering of this stronger or broader immunity." Vaccines teach the allowed system — which includes both antibodies and T-cells — to recognize part of a virus. A T cell is a blazon of white claret cell that responds to viral infections and boosts the immune function of other cells. A single dose of either the AstraZeneca or Pfizer shots has been found to generate a significant antibody response to the novel coronavirus. But a recent written report by the U.One thousand. Coronavirus Immunology Consortium and the Academy of Birmingham found that the AstraZeneca vaccine may actually induce a stronger cellular immune response than the Pfizer shot. So a combination of the 2 shots "could pb to a higher quantity of antibody, but it can besides broaden the allowed response," Fletcher said. Yes. Fletcher said people take been combining vaccine types for several decades in an effort to boost immune responses to malaria, tuberculosis, HIV and cancers. A mixed vaccine regimen was canonical for Ebola last twelvemonth. "When we give immunizations to infants, we use several dissimilar types of vaccine over a menses of months and years with no condom concerns," Fletcher said. Fletcher said there accept been no reports of any side effects across the ones already reported when the vaccines are administered individually. "The Com-COV study will, of form, be looking very closely at rubber and it's neat that this is existence advisedly monitored as function of a clinical trial, simply I would not anticipate any safety problem with mixing vaccines," she said. Different vaccines administered as function of a 2-dose authorities do non directly interact with each other, as the vaccine particles are swiftly cleared by the allowed system within days of immunization, Fletcher said. "There's no remaining vaccine mRNA or vaccine viral vector around when y'all requite a second dose," she said. Jorg Fritz, a microbiology and immunology professor at McGill University, said he doesn't come across why there would be any boosted danger involved in receiving two dissimilar vaccines. Fritz said he also thinks it would exist ameliorate to mix two vaccines that utilize different technologies than to expect besides long to give the 2d shot. "I retrieve it's more important to get a booster vaccination to have a more robust and more than durable immune response confronting the viral proteins than using the aforementioned technology," Fritz told the Canadian Press. Dr. Theresa Tam, Canada's chief public health officeholder, said concluding week the current guidance is for AstraZeneca recipients to get a second dose of the same production, but NACI is now reviewing the Oxford research on mixing AstraZeneca with an mRNA shot. "There volition exist further advice forthcoming on that 2nd dose based on the evolving science. We should sentry this space," Tam said. "All of the vaccines being used in Canada are targeting the virus' fasten poly peptide, so I think the science volition look not just at whether the mixed schedule is safety, but whether that's actually an fifty-fifty improve approach than using exactly the same vaccine for the two doses. Those questions remain to exist answered." Probably. According to Health Canada, at to the lowest degree i,540,000 AstraZeneca doses have been administered in Canada as of May one. Thousands of Canadians take been vaccinated since and then. With commitment of millions more mRNA shots expected over the coming months — Pfizer alone will deliver two million shots each week in May before ramping upwards to 2.4 million a week adjacent month — there should exist plenty shots on hand to vaccinate AstraZeneca recipients with a second dose of a second product. But provinces may accept to agree back some Pfizer supply to brand this work. Canada has ordered 48 million Pfizer doses — 5.5 million were delivered in the January-through-March menstruation, 24.2 million will arrive in the second quarter of this year and xviii.3 million more than are to follow between July and September. That's enough shots to vaccinate 24 million people with ii doses. If some of that product is earmarked for people who already have doses of AstraZeneca, that leaves less product for outset doses. Moderna is also expected to deliver 12.3 million doses of its mRNA product in the April-through-June period, with millions more doses expected in the tertiary quarter of this twelvemonth. WATCH: Canada will before long have enough doses to offer vaccines to all who want them Maj. Gen. Dany Fortin, the armed forces commander leading vaccine logistics at the Public Health Agency of Canada, said last Th that officials are "just starting to practice deliberate planning on second doses." "What I would tell you is provinces and territories have a proficient handle on what they need. They proceed tabs on who is getting which vaccine," he said. "Everybody is working on a very deliberate plan making sure people become the right vaccine when they're supposed to receive it." Possibly. NACI said in early March that, given the express vaccine supply, provinces and territories may desire to expect up to 16 weeks between first and 2d doses to give more people at least some level of protection. The provinces take since followed this guidance, with a few exceptions. For case, many long-term care home residents accept been fully vaccinated on the timeline recommended by the vaccine makers. Pfizer calls for a second dose 21 days afterwards the first, while Moderna stipulates the 2nd shot should come 28 days afterward. Ontario appear Monday that it would begin offer second doses to some high-gamble groups this calendar week. "As more vaccines come in, that interval can be shorter," Tam said.
What does the research say about mixing vaccines?
The prospect of a 'stronger immune response'
Is there any history of mixing different vaccines like this?
Are there any risks associated with a mismatched regimen?
What have Canadian officials said about this?
Would nosotros have enough mRNA doses for a mix-and-friction match program?
Volition Canada shorten the time between shots?
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Source: https://www.cbc.ca/news/politics/vaccines-mix-and-match-1.6020986
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