what's building >> this is abc seven news. kristen: i'm kristen sze. you are watching getting answers. we ask experts your questions every day to get answers in real-time. today we will talk to an epidemiologist who went viral for her tweets explaining through simple math how delta has changed many things, including the percentage of people we need to vaccinate. we said math, but unlike barbie, we think math is fun and important. the president of navajo nation will join us to talk about how native americans went from having some of the highest covid mortality rates to having the highest vaccination rates in the u.s., a success story that maybe we can all draw from.

a major headline, san francisco has become the first city to net -- to mandate vaccines for anyone entering high-risk indoor settings like restaurants, gyms, for customers and employees. joining us to talk about this is the department medicine chair for ucsf. >> good to be here. kristen: this is another first for san francisco, the first city to ban large gatherings. do you think this is necessary or unnecessary at this point, given our vaccination point? >> necessary. we have to do more than we are doing. we are seeing a surgeon san francisco. we have a lot of people vaccinated. it is not even enough, although we are at 70% vaccination rate. what is new about this mandate is unlike the new york mandate, it will require people get both shots. i think that is why, because you

can have the illusion that you have gotten one-shot and you are protected. the first shot doesn't protect you in the face of delta. you need to be fully vaccinated. kristen: talk about the differential between effectiveness between one-shot and both shots. >> in the early days, the u.k. gave people their first shot and waited a few months to give their second shot. they wanted to give more people the first shot because against the original virus, the first shot worked pretty well. you were 80% protected a few weeks after the first child. the second shot got two to 95%. with delta, the first shot does very little. people should not feel like they are protected after the first shot. it isn't until after your second shot that you reach a reasonable level of protection. people can sometimes have the sense that they are safe after the first shot but it isn't until after the second shot that you are reasonably safe against delta.

you are not perfectly safe because the efficacy of the vaccines has gone down some in the face of delta. kristen: i want to explore that a little later. i want to ask, one thing i noticed that is different about the mandate is unlike the state mandates for health care workers or teachers, a negative test is not good enough. don'ant to show your vexing proof, it is not like you can show a negative's -- a negative test. >> it is a judgment call on the city's part. having a negative test that day is reasonably good proof that you are ok. it is not perfect but it is reasonably good. as a city making a statement that we want people to get vaccinated, we really don't want give people an out. everybody should be vaccinated, so giving people a mandate that if you want to go into a restaurant or jim, you need to be fully vaccinated, it not only keeps the settings safe but moves us in the right direction to get more people vaccinated. kristen: mandates are a

balancing act. on one hand you have to consider the business interests that in this case, do you think it would make you more or less willing to enter those businesses knowing you have to show proof? >> the folks running hamilton downtown invited me and a bunch of people to come to the show in the last couple days which was magnificent. they require proof of vaccination and everybody was wearing a mask. i saw the show, and absolutely loved it. you should go if you have a chance. i would not have gone if they didn't require vaccinations. for me and i think for a lot of people, they will be more comfortable going to an indoor space if they know everybody has been vaccinated, than if they don't know. there will probably be, they will probably lose some people who don't want to have that mandate but i think they will have a better business if they mandate it. kristen: i should have known you were not going to throw away your shot. >> no, thank you very much. that was a hanging curveball. kristen: low hanging fruit.

i do want to ask, if you think this impetus, this will serve as an impetus for other counties to follow, even the state or the federal level, to copy san francisco. >> the bay area has tended to act together on these sorts of things so i wouldn't be surprised if other bay area counties, which have also been quite progressive and aggressive about doing what needs to be done to keep covid in check, i wouldn't be surprised if they follow. we will see. i think san francisco has often been at the forefront of some of the public health measures. part of the reason is that we can get away with it here because the public is on board and there isn't the same politics that exist in other parts of the country. i don't think you could do this in texas or florida today. kristen: one thing i looked at with today's decree, the mayor says a photo of your cdc card is enough asof. how concerned aine cards? >> concerned.

they are easy to come by andparm comfortable going to an indoor space with the vaccine mandate is that i trust that that is now a much safer space than without it. if i felt like 20% of the people are faking it, then i would trust it less. i think there should be a digital verifiable trustworthy system so people can have a little card -- can't have a little card or picture of a card. until we have that i think this is the best we can do. kristen: you were talking about waning vaccine efficacy. that is a concern to a lot of people. what do we know? >> there are two important numbers to pay attention to. the good news first, the vaccines continue to be very effective in preventing you from getting very sick, going to the hospital and dying. in many ways, that is the biggest thing we care about. the efficacy is a little bit less than it was in the pre-delta days, but not much

less. the vaccines, i'm fully vaccinated and i feel comfortable i will not go to the hospital and i of covid. what has waned is the overall efficacy against symptomatic infections. for someone who has been vaccinated, we call that a breakthrough infection. that number was about 95% efficacious when the pfizer and moderna results came out. the studies are a little all over the map but that number is no longer 95%. whether it is 80%, 70%, or lower is a little up in the air, but it does say for a vaccinated person now, you are very protected against getting very sick and blessed well person -- part -- less well protected. against getting a case of covid. i don't even want a mild case so that is partly why i'm still very careful with masking and other things. kristen: our viewer has a fact

check question. she wants you to explain why so many vaccinated people are giving -- getting everyone sick and why so many vaccinated people are sick in the icu. you explained that there are people who are vaccinated that are getting sick, but their symptoms overall are much better the less severe and outcomes are much better than those who didn't get vaccinated. >> correct. the people we are seeing in hospitals now are largely unvaccinated. there will be a few vaccinated people that slip through because it is not 100% perfect protection of the more people you have vaccinated, the more likely it is you will have someone who is hospitalized who has been vaccinated. if 100% of people are vaccinated, everybody in the hospital will be vaccinated that if you go to ucsf, and we have 40 patients in the hospital, the vast majority are unvaccinated although san francisco, 75%-80% of people in san francisco are vaccinated. you are well protected but there

can be some cases that breakthrough. kristen: vivian wants to know, how about those people who can't get vaccinated for medical reasons? does that mean they can't go to indoor places in san francisco? >> i think it probably does. there are very few medical reasons why someone can't be vaccinated. when we look at the indications like fancy medical speak for you can't take the vaccine, it is a very very small number. most people, if they have had allergies to a prior vaccine, can take this vaccine. the group i worry about are people who actually have been vaccinated but the vaccine did taycan those are people who will -- didn't take and those are people who are immunocompromised. it is recommended they get a third shot. kristen: i was going to ask you about that. i think the fda authorization will come in a second for immunocompromised people to get the third shot. how could -- soon could they get those in arms? tomorrow, this weekend? >> i think it is the fda

authorizing it, then the cdc blessing it and it is the same shot so it is going to your pharmacy and demonstrating you are immunocompromised and asking for the third shot. i wouldn't think there would be a long delay. if i was immunocompromised, like an organ transplant or lupus, on medicines that lowered my immunity, as soon as i was eligible to get the third shot, i would get it. kristen: if you got the johnson & johnson, would you get -- >> you would get a pfizer or moderna. it may turn out that we have boosters for everybody who got shots for the johnson because it is overall, the efficacy started lower than pfizer and moderna. the booster for that group will be pfizer or moderna, not another shot of johnson & johnson. kristen: great talking to you today. i know you are eager for our next guest, who will explain the civil math, why delta has changed angst. thanks for joining us today.

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kristen: earlier in the pandemic experts hoped if we could get 75% of americans vaccinated, we could contain covid. today we are just over 50% but 75% is no longer enough. the delta variant has changed the equation, literally. a professor of epidemiology recently tweeted equations that explain why delta has made it mathematically impossible to

beat the virus now with just the vaccine. joining us is dr. ellie murray to share her calculations. thanks for joining us. dr. murray: glad to be here. kristen: many people fear math but if we don't get the math we don't get why case numbers are going up and why we are seeing more mandates. give us your five minute lesson on how to think about delta changing the pandemic picture. dr. murray: the important piece of math we need to think about in an outbreak setting kamala covid and other pandemics, is the idea of, what is the average number of people that someone with the virus would infect? with the original strain of covid that was circulating over the last year, february, march, through the summer, we expected that was maybe about three people on average would be infected. we were aiming for 75% of people to be vaccinated with a 95%

effective vaccine to get the number below one. kristen: i think we have an equation we can throw up. once you can ■see that, you can talk to us about the numbers in the equation. there it is. can you see it? re, that is the reproductive rate, equals three, that is three is how many people infected? dr. murray: exactly. kristen: times one -0.7 5 tell us what those numbers mean. dr. murray: the numbers in the parentheses, that is a way to calculate comedy people are susceptible to covid. -- how many people are susceptible to covid. one is 100 percent of people. we will subtract those who have immunity so currently 50% are vaccinated so we can take 04 -- 0.5. the vaccine is not 100%

effective. no vaccine is 100% effective but covid vaccines are great so there may be 95% effective. we adjust the number down a little. we wind up with 0.5 times 0.95 to give us how many people have immunity and we subtract that from one to get the proportion of people who are fully susceptible. kristen: re re re re re re is over one. i have been told you need to keep it under one to beat the virus. this is not great, but that 50% vaccination which is what we have. what if we had 75% vaccination? it is under 1, 0 point 86. that means we would beat the virus? dr. murray: if the number is under one, that means whenever someone is infected, the number of people they infect will be less than one and that means the

outbreak will go kind of away on its own. there may be occasional flareups but they will be straightforward to control. that is the sweet spot where if we can get covid below one we don't have to worry so much about our other precautions. kristen: now we have the delta. that is a different equation. let's see what delta is doing with the current 50% vaccination rate. we are at 50.9 but it is close enough. walk us through what we are looking at with the re being 4.6. dr. murray: a couple numbers have changed. instead of three people on average being infected by someone who has the delta variant, which is what we saw with the original strain, if we don't account for immunity we expect up to eight people to be infected by each infected person. we add in the number, multiply the number in the parentheses to account for vaccination, but we have to change now 95%

effectiveness, we have to decrease that because delta is more contagious and harder to control. we could maybe guess that is about 85%. we have seen some numbers come out in the past few days that are changing that number a little, but 85% is a reasonably, maybe a little optimistic number. if we put that number in, what we find is with 50% of the population vaccinated, the reproductive number is 4.6. a lot bigger than what we saw in the beginning. kristen: that is not good. even if we increase vaccination to 75%, which is a stretch based on what people are saying, that only gets us to 2.9 reproductive rate. so one person who has the delta variant will give it to almost three people. even that, i have to ask, if we can put in 100% vaccination rate, will that bring us down to under one? is that not going to do it? dr. murray: with the delta variant that won't do it.

because the delta variant is so much more infectious than the original virus that was circulating, even getting 100% of people vaccinated would not bring that down below one. what that means is, a lot of people here that and it feels scary, this will go on forever. we have to remember that this spring, last spring and summer, we were able to bring a three down below one in a lot of areas with masking and temporary restaurant closures and temporary event closures. if we can get as many people vaccinated as possible to get the number close to one, we can use our other tools to get it down below one. kristen: all hope is not lost. what if we got boosters? the fda is about to authorize boosters for the immuno compromised and may be soon for others. if we got the 50% that have vaccines a booster, so we bring up the efficacy a little, does that help a lot?

a little bit? dr. murray: that doesn't help very much at all on the overall society level. what we are taking is, that equation where we have eight times one -0.5 times 0.85, we are changing the 0.85 to maybe zero .9, 90% effective, maybe 95% effective, that would be a bit of a stretch but that doesn't change the numbers much. we wind up above four with that effective number, even if we give everyone who has already had the full dose of vaccine, if we get them all boosters. kristen: that is why we are getting this message, get more people vaccinated and take those other mitigation measures and together, bringing it closer to one. dr. ellie murray, thank you so much. for people who don't think math is important, there it is. it is important. i appreciate you sharing this. dr. murray: thanks for having me. kristen: coming up next, a

success story. native americans took a complete 180. we will talk to the president of the navajo nation, next, about

kristen: early in the pandemic, native american communities had high infection mortality rates but that has turned around completely. native americans have the highest vaccination rates in the country. joining us to talk about how this accomplished, we are honored to have the president of the navajo nation, jonathan nez, from arizona. thank you so much for your time. it is an honor to speak with you. we can't hear you so we are ng to tweak that. is it coming from his end? the audio? president nez: we are here in arizona at one of our own health care facilities. thank you for having us on the show. kristen: absolutely.

you are at 70% vaccination rate right now, the navajo nation. i want to ask how you got there. how did you manage such a high rate in terms of both how you did it, like boots on the ground, getting it to people but also, overcoming any resistance or doubts? president nez: on the navajo nation, we as leaders got on film, got on camera and actually took the vaccine on camera to bring confidence to the shot. many of our navajo citizens throughout the navajo nation got their questions answered, and we did have folks like dr. fauci on our town hall meetings, a lot of our health care professionals answering those questions. and we framed it in a way to where we are not just taking a vaccine for ourselves, but for our family, her our communities and for our nation.

kristen: i was going to ask you about the cultural values. where there stories that you drew from or cultural beliefs that you really put it out there to the people? president nez: we use our way of life teaching and our history. we pushoff on these monsters that plagued our navajo people since time immemorial, utilizing that teaching. covid-19 is a modern-day monster . with the vaccine and wearing our masks, that is the armor that protects us from these various monsters and of course, the weapons to fight back is these health care protocols that the cdc recommended. we have had a mask mandate for over a year now. that has never changed. of course, know that we are seeing the uptake across the country, we are very concerned.

the thing that is different now is that we didn't have the vaccine when we were getting the large increase of covid positive cases like we had seen on the navajo nation. kristen: let me ask you, i don't want to generalize but do you think there is something you can draw upon in native american history, cultural values where if you look at the debate of, it's my right, versus the collective good, how does the scale tip? president nez: here on we don't politicize wearing masks. we didn't say our rights were being infringed when we were told to stay home. it was about protecting our families. it was protecting our community, and keeping our navajo nation safe. we didn't have people picketing or protesting about their individual freedoms, but it was

more about the larger good for communities, to be able to protect our citizens and to protect our younger generation, those that are the most vulnerable population. kristen: jonathan nez, president of the navajo nation, congratulations on your successes and thanks for sharing your experience. don't go away because we will continue to

at usaa, we've been called too exclusive.

because we were created for officers. but as we've evolved with the military, we've grown to serve all who've honorably served. no matter their rank, or when they were in. a marine just out of basic, or a petty officer from '73. and even his kids. and their kids. usaa is made for all who've honorably served and their families. are we still exclusive? absolutely. and that's exactly why you should join. kristen: thanks for joining us. we covered san francisco's vaccine mandate, vaccine effectiveness, and we did some math to find out how difficult it is to beat the delta variant with vaccines alone. we talked to the president of

the navajo nation about native americans having the highest vaccination rate in the country and how they did it. world news tonight is next. we will see