There are three lines of evidence that I wish to offer for my claim. First, consider the efficacy of the vaccine. The efficacy of the two mRNA vaccines is superb, offering 95% reduction in the rate of acquisition of symptomatic COVID-19 in randomized trials. That is a remarkable result. But the key statistic here is one step beyond the vaccine efficacy. If you get two doses of the vaccine, and if you remain asymptomatic 14 days after the second dose, what is the probability you will develop COVID-19? For Moderna, the answer is there is a
99.92% chance that you won't. Only 12 cases occurred after this time in 14,550 actively vaccinated people in the trial, while the control arm experienced nearly 3.5% cumulative incidence. For Pfizer, only eight cases occurred amongst people who had completed a second dose and went 7 days without symptoms, again a
99.95% chance of not getting COVID if one remained asymptomatic a week after the second dose. In other words, if you get 14 days past the second dose, and feel fine, the likelihood you will get COVID-19 in these studies is very low. Some argue that in the real world -- where folks are not as motivated as trial participants -- the rate of SARS-CoV-2 acquisition might be higher, and thus relaxing rules riskier. But this logic cuts both ways: if people in the real world are less compliant, then the rules might be relaxed no matter what we say.
Next, consider the risk of spreading SARS-CoV-2 to others. That risk is in part driven by symptomatic infections which are exceedingly rare after second doses. Risk of spreading is diminished by the brisk immune response that occurs after symptomatic infection once someone is vaccinated. In the Moderna study, there were 30 cases of severe COVID overall and zero in the vaccination arm. Less symptomatic and less severe COVID will result in a lower propensity to propagate SARS-CoV-2. Moreover, studies of both
recombinant antibody products speed viral clearance from airways. If the body is primed to manufacture anti-spike antibodies through vaccination, there is likely a similar rapid clearance and subsequent reduction in infectiousness occurs.
What about asymptomatic infection and so-called silent spread? In the Moderna trial, swabs taken from asymptomatic participants as they were receiving dose 2 showed a roughly 60% reduction in
PCR positivity. It is likely that a second dose and longer asymptomatic period will result in greater reduction in PCR positivity.
Preliminary data from AstraZeneca's ChAdOx1 vaccine also showed reduced in asymptomatic PCR detection. In short, it is highly likely that receipt of vaccination and a 14-day asymptomatic period afterward results in both personal protection and reduced likelihood of ongoing viral propagation.
