Thread by @SherOnHealth

Real-world American study of 91,134 people finds one dose of Pfizer/Moderna protects MUCH LESS against death/hospitalization then two doses in 3 or 4 week intervals.
The finding should raise questions about Canada delaying doses 16 weeks.

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medrxiv.org/content/10.110…

Some health officials, including @Healthmac defend the delay pointing to a less robust study that counted as one-shot immunized those who had a dose but who were hospitalized or died before the two weeks that shot needs to build an immune response but now the verdict is in...
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The new study did NOT count people as having gotten one dose unless they were fine for 2 weeks before illness began. Those who got sick in the first two weeks were counted as not vaccinated at all. The one-dose group was limited to those who were health 2+weeks after 1st dose
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The new American study was not only large and robust but also one that better represented the population as a whole with a focus on effectiveness after both one dose alone and two dose. It is the best evidence available and public health in Canada should take heed.
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The American study tracked hospitalizations and deaths for 11 weeks and while one shot alone cause rates to plateau, it did so at a level considerably above the group who received two shots in 3 or 4 weeks.
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Among 23,139 Americans who received both doses, one died. Among 4,058 who received only one dose and were fine the next two weeks, five died, and while that difference might seem small, it's not when multiplied by the millions of Canadian waiting 16 weeks for a 2nd shot.
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None of the math or science changes the fact that Canada is far behind the US in securing timely vaccines, and that shortage creates tough choices; we can't get everyone two doses quickly. But this study should drive public health to do two things ...
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Canadians w/high-risk health conditions such as diabetes, Crohn's disease and obesity (and not just morbidly obesity) should get their 2nd doses much sooner than 16 weeks, because other studies show they are far more vulnerable
medrxiv.org/content/10.110…
nejm.org/doi/pdf/10.105…

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Dr. Tam @CPHO_Canada earlier today said Canada might re-open this summer w/20% of people getting two doses.
She needs to review the new American study and revise her approach. One dose is significantly less effective, and if we ignore that, we risk a 4th Fall wave. #COVID19
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