Canadian government switches to support for first doses first

The summary:<p><pre><code> While studies have not yet collected four months of data on vaccine effectiveness after the first dose, the first two months of real world effectiveness are showing sustained high levels of protection. ... Short term sustained protection is consistent with immunological principles and vaccine science where it is not expected to see rapid waning of a highly effective vaccine in adults over a relatively short period of time. Extending the interval between doses was shown to be a good strategy through modelling, even in scenarios considering a six month interval and in theoretical scenarios where waning protection was considered. NACI recommends that in the context of limited COVID-19 vaccine supply, jurisdictions should maximize the number of individuals benefiting from the first dose of vaccine by extending the interval for the second dose of vaccine to four months. </code></pre> So basically, it makes theoretical sense, looks beneficial in total, so let&#x27;s consciously adjust the vaccine administration regime we studied.

I&#x27;ve been fairly disappointed with the analysis of first doses first. If someone were to recommend half-courses of antibiotics, I feel like a lot more people would instantly recognize what could potentially go wrong here (and for which we will have &#x27;no evidence for&#x27; until it is too late). The assumption of first doses first is that partial protection is better than all or none - but with evolving organisms, this is a pretty tendentious assumption. It is not at all implausible that this strategy will select for vaccine-immune strains.

The better argument for first doses first is the expectation that vaccine supply and delivery will rise significantly in the near term. This would allow a country to start everyone’s vaccination timeframe sooner with a strong expectation that supply would bring second doses closer to the normal timeframe over time.<p>It sounds like Canada’s approach is aware of this as it is “extending the second dose of COVID-19 vaccine up to four months after the first.”<p>This maximum of four months is a solid approach because either (1) the science is solid and net more protection is offered to the country, or (2) the science is just ok, but the supply and delivery improvements will actually allow for on time doses at a faster pace then previously possible