"Parks then comes to the central thesis of her testimony: that COVID-19 vaccines do not prevent transmission. This claim is false and readily verifiable as such. Firstly, as a baseline, if infection cannot occur (sterilizing immunity) then there is no potential for onward transmission. mRNA vaccines in particular have demonstrated the ability to prevent infections. This study found that 14 days after the second dose of an mRNA vaccine, the risk of a positive PCR was 90% lower than for an unvaccinated individual. Johnson and Johnson/Janssenís pre-licensure Phase 3 trial measured an efficacy of 65% against asymptomatic infection. A study of Mayo Clinic patients found that 10 days after 1 dose of mRNA vaccination, the risk of a positive PCR was reduced by about 80%. In a nationwide study in Israel, the Pfizer vaccine was able to reduce asymptomatic infection by 90% 7 days after dose 2. The SIREN study of UK healthcare workers confirmed that the Pfizer vaccine is able to reduce the risk of asymptomatic infection by 85% 7+ days after the second dose. There are additional data to assess transmission risks. This study showed that for every 20% of the population that is vaccinated, the risk of an unvaccinated person having a positive PCR is halved. This study found that the the likelihood of household transmission was approximately 40 to 50% lower in households of index patients who had been vaccinated 21 days or more before testing positive than in households of unvaccinated index patients, with most of the vaccinated participants having received just 1 dose of vaccine in a 2-dose series. This summary by Richterman, Meyerowitz, and Cevik goes through a great deal of the data on the indirect effects of COVID-19 vaccines to stop the spread. In fact, Dr. Cevik herself recently contributed a thorough Twitter thread on how the picture may have changed with the Delta variant- but by and large it hasnít. This alone would be sufficient to dismiss Dr. Clarkís entire testimony but she makes a number of additional false claims which also should be addressed. "