But there are also other threads of evidence that are important to think about as well. We're seeing early signs in the evidence that the Pfizer vaccine protects against infection and, therefore, reduces a person's ability to transmit the virus. This is a hard-to-measure part of the vaccine, but there are a variety of different pieces of evidence coming in. For example, initial evidence from the UK found that there was an 86 percent reduction in infection for recipients of the Pfizer/BioNTech vaccine. Similarly, early published but not peer-reviewed results from Israel show an 89 percent reduction in infection. Both symptomatic and asymptomatic cases were measured. These sorts of results suggest that the vaccine recipients may not be able to transmit the virus, and it gives us the sense that it may be possible to achieve herd immunity through use of the vaccines.