Different approach from many other VE studies, following HCW vaccinated vs unvaccinated, tested when exposed to a case, to assess VE against infection given exposure, consistent with our recommendations in sciencedirect.com/science/articl…
Also looked at infectiousness (proxied by Ct). Take home messages: fully vaccinated 65% (45-79) protected against infection given exposure. This is lower than other estimates of symptomatic or arbitrary mix of symptomatic and other cases, as expected.
(this was before Delta). The "all infections" outcome in many other studies is really not all, but all that are ascertained passively. This was active surveillance so gets a higher % of low/asymptomatic cases and thus expected to have lower VE (see the Vaccine paper for more)
2. We found 70(43-84)% VE against infection with any Ct<30 perhaps indicating infectiousness. 3. Median Ct ~5 lower for fully vaccinated (breakthru) cases vs. unvaccinated. Could mean shedding <10% as much virus, thus less transmissible.
4. Small numbers but interesting: Antigen test positivity was 80% in Ct<30 if not vaccinated, but only 31% in Ct<30 if vaccinated, perhaps indicating that infectivity was even lower than the Ct values indicate (if Ct is measuring more dead virus in vaxed cases).
Overall very encouraging for transmission reduction by mRNA vaccines, via a combo of preventing infection and reducing infectiousness. Obviously key to know if the same will be true with additional variants.
Correction to #4 above: thanks @vercheckt indeed the numbers given are for all PCR+ 32% (correctly rounded) of vaxed vs 80% of unvaxed were antigen test+
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