there are multiple vaccines against covid-19. i’ll focus on the moderna and pfizer-biontech mrna vaccines used in canada. they both received emergency use authorization from the u.s. food and drug administration (fda) and health canada in december 2020. the pfizer-biontech vaccine also received full fda approval in august 2021 . now that it is fully approved, the pfizer-biontech vaccine is also known by a brand name — comirnaty — but it’s the exact same vaccine that’s been in use since december 2020.
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both the moderna and pfizer-biontech vaccines require two doses given at least three to four weeks apart. the mrna (or messenger rna) in the vaccines contains the instructions for how to make the now-well-known spike protein on the surface of sars-cov-2, the virus that causes covid-19.
these numbers are the actual numbers out of the pfizer-biontech trial , which reported 95 per cent efficacy in its clinical trials. moderna reported a similar number (94.5 per cent efficacy) in its trials.
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vaccine efficacy is usually measured under specific controlled environments and in the setting of double-blind randomized controlled trials (rcts). a double-blind rct is a study in which the participants are randomly assigned to either a placebo (no vaccine) or intervention (vaccine) group and neither the researchers nor the participants are aware which group they are assigned to. this setting reduces bias and increases the accuracy of the studies.
it’s worth noting that most studies have defined developing disease as testing positive for covid-19 and having at least one symptom. the efficacy numbers can change based on the circumstances under which the vaccines are tested. for example, the location of testing, the method of testing, the presence of specific strains or variants of a disease-causing virus and the diversity of the participants can affect the efficacy numbers. that’s why demographic information is collected in clinical trials, including moderna ’s and pfizer-biontech ’s vaccine trials.
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with more than five billion doses administered around the world, we are at a point where we can also look at the effectiveness of the covid-19 vaccines. preliminary studies have shown that both mrna vaccines are about 90 per cent effective in the real world against covid-19. the alberta government has reported 93 per cent effectiveness from the moderna and 90 per cent effectiveness from the pfizer-biontech vaccine.
and why does it take two weeks to develop that level of immunity? the process of a vaccine making our bodies immune against a disease has multiple steps . remember the protective proteins called antibodies? one of the last steps in the immunity process is making those antibodies.
based on the studies done by the vaccine makers , at around 14 days after the second dose, our bodies have made enough antibodies to recognize and fight sars-cov-2, hence the two-week rule before you are considered fully vaccinated.
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another question i’ve been asked is how the effectiveness from the covid-19 vaccines compares to the vaccines made for other diseases. well, the mmr vaccine is 97 per cent effective against measles and rubella and 88 per cent against mumps . the effectiveness of the dtap vaccine (diphtheria, tetanus, acellular pertussis) is between 80-85 per cent . the effectiveness of the flu vaccine hovers between 10-60 per cent depending on the year, the strains the vaccine protects against each year and the actual strains causing influenza and influenza-like diseases.
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