cdc did in its guidance about close to two months ago now is based on the science saying that your risk of getting sick or transmitting the virus was low if you were fully vaccinated they gave communities and individuals the flexibility to make decisions about what to do with masks now in areas where there are low numbers of vaccinated people or where cases are rising its very reasonable for counties to take more mitigation measures like the mask rules that you see coming out in la and i anticipate that will happen in other parts of the country too should also say martha that for individuals as well depending on their circumstances some people may choose to continue wearing masks such as those who may be immunocompromised or people who have those family members at home who are unvaccinated so people can make these decisions counties certainly have the right to put mitigation measures back in place and thats not contradictory to the guidance the cdc has issued raddatz rochelle walensky head of the cdc says this has become a pandemic of the unvaccinated but we have seen a number of cases reported in vaccinated individuals how rare is that and is there growing concern with those numbers of vaccinated people who are getting covid murthy well martha the vaccines that we have against covid are highly effective in the case of the mrna vaccines more than 90 percent effective in preventing symptomatic infection but theyre not 100 percent perfect no vaccine is and that means you will see some numbers of people who have breakthrough cases but there are two things to know about that one is that these numbers will be small keep in mind we vaccinated millions and millions of people in the united states we have in fact more than 160 million people who are fully vaccinated right now so you will see numbers a minority a small minority of people who are who do have breakthrough infections but heres the other thing to know is that when youre fully vaccinated even if you do have a break through infection its much more likely that infection will be either asymptomatic or mild and thats really good news that continues to tell us that these vaccines are highly effective and thats one of the reasons we are recommending them for people across the country raddatz do you believe that part of these new mask mandates for the vaccinated like in la county is because theres just no way of telling whether unmasked people are vaccinated or not is that part of the problem here murthy well i think for communities where theyre seeing a significant increase in cases la county is one of those counties i think theyre looking to take mitigation measures to reduce that spread and masks are one of them look when you have we saw this during the last year of the pandemic that when you have