蜜柚直播

Statewide weekly vaccine doses administered April 11-17 fell by about 13%, according to the 蜜柚直播 Department of Health Services鈥� online chart of COVID-19 vaccine administration, as of Friday. The chart includes both first and second doses.

Countywide weekly doses administered fell by 17% over the same period, according to Pima County vaccine data.

The number of immune people needed to reach herd immunity has been hard for health experts to pin down, but it includes some combination of those who have been vaccinated and those who have been infected by the virus.

As of Friday, about 39% of the state and about 45% of the county have received at least one dose of COVID-19 vaccine, according to ADHS data.

A 鈥渧ery significant proportion of our population鈥� has also been naturally infected, said Dr. Francisco Garcia, Pima County鈥檚 chief medical officer.

Estimating the true number of natural infections, however, would be very difficult to do with any sort of precision, he said.

He also avoids equating natural immunity with vaccine-induced immunity, he said. 鈥淭hat protection that you get from this normal infection may not be as strong as the protection that you get from vaccination.鈥�

Elusive threshold

Whether or not health experts think herd immunity is still achievable depends on how they define it. They don鈥檛 have one shared definition.

鈥淣o one knows exactly what the magic number is,鈥� said Michael Worobey, head of the University of 蜜柚直播鈥檚 Department of Ecology and Evolutionary Biology.

鈥淚f we define herd immunity as a level of natural and vaccine-induced immunity that will make it impossible for the virus to spread in the U.S. I don鈥檛 think we鈥檙e going to get there.鈥�

This is a more strict definition of herd immunity, akin to the outcome of the vaccination program that eliminated polio from the U.S.

A more relaxed definition of herd immunity is more achievable, one where enough natural infections and vaccinations prevent massive surges in COVID-19 cases, said Dr. Joe Gerald, an associate professor with the University of 蜜柚直播鈥檚 College of Public Health.

By this measure, herd immunity is possible, he said. 鈥淚 think there are enough people who are either naturally immune or vaccine immune that we鈥檙e just not gonna see the same size and scale of outbreaks.鈥�

Either way, new more contagious variants have moved herd immunity鈥檚 goalpost, increasing the number of immune people we need to achieve it.

鈥淟et鈥檚 say it was 75% before more transmissible variants and variants that have some degree of immune escape emerged,鈥� Worobey said. 鈥淚 would imagine it鈥檚 closer to 90% now.鈥�

Researchers at 蜜柚直播 State University recently modified their forecasting model to account for a new, more contagious variant, known as B.1.1.7, that originated in the United Kingdom and has established dominance in 蜜柚直播, according to a written by Tim Lant, who is one of the ASU researchers, and Will Humble, who is the executive director of the 蜜柚直播 Public Health Association and former state health director.

Now the ASU researchers estimate the herd immunity threshold is around 80-85%. They had originally estimated 75%.

鈥淲e think herd immunity means that disease transmission starts going down on its own (without interventions in place) because there鈥檚 enough immunity in the herd to block just enough secondary (and tertiary, etc.) transmission that it burns out the continued spread,鈥� Lant and Humble wrote.

They explain that we鈥檒l know we鈥檝e reached herd immunity once life goes back to normal, we remove our masks, case counts continue to fall and the average number of people that someone with COVID-19 infects falls below one.

This average number is known as the Rt value, or effective reproduction number. Infections slow when the Rt is below 1. The website estimated the current Rt in 蜜柚直播 was 1, as of Friday.

鈥淚deally, policy makers would keep non-pharmaceutical interventions like mask wearing and limited indoor capacity in crowded bars, nightclubs, and restaurants until the R values are less than 1,鈥� Humble and Lant wrote. 鈥淥ur governor and health director have already eliminated every single required mitigation measure except for vaccinating people.鈥�

Virus 鈥榚ntrenched鈥�

While some people are voluntarily following recommendations, like wearing a mask and social distancing, COVID-19 cases are rising across 蜜柚直播, although they are not surging exponentially.

As Gerald put it, they are rising 鈥渓inearly.鈥�

The more chances the virus has to spread in 蜜柚直播 and around the world, the more chances the virus has to mutate into even more concerning variants.

Worobey is optimistic that the vaccines, particularly the mRNA vaccines, such as Moderna and Pfizer, will protect against new variants over the next several years.

For most people, these vaccines protect against the current variants for a long time, he said, adding that he is not less optimistic about the Johnson & Johnson vaccine, it鈥檚 just a minor player compared to the other two.

鈥淲e will have to continue to monitor how long protection lasts, but it is very possible that boosters will be needed less frequently than for flu,鈥� he said.

鈥淚 think it鈥檚 pretty clear at this point that this is going to become entrenched in the human population, something like influenza is. And we鈥檙e going to be managing it. And the more people we can get vaccinated, the less of a toll that鈥檚 going to take.鈥�

2 big obstacles

Vaccine hesitancy and the logistics of vaccine delivery are the two big hurdles right now to getting more people vaccinated, Gerald said, adding that the vaccination strategy needs to change to reach people wherever they might be.

Pima County health workers are working to answer questions and debunk myths to reassure those who are hesitant about COVID-19 vaccines, said Jess Seline, the county鈥檚 health equity program manager.

鈥淣ow we鈥檙e in more of the territory of folks who are potentially willing to get it, but just kind of need more time and information,鈥� she said.

The county has already vaccinated those who were initially very eager to get vaccinated, said Garcia.

鈥淚t鈥檚 just gotten a hell of a lot harder to do vaccines because all the low hanging fruit has been picked off,鈥� he said. 鈥淲e are having to work four times as hard for every vaccine that we get into someone鈥檚 arm.鈥�

The county is trying to make it as easy as possible for anyone to get vaccinated who has thought about getting vaccinated, he said.

鈥淲e鈥檙e hoping to make vaccine opportunities so ubiquitous throughout our community, whether it鈥檚 on Fourth Avenue, whether it鈥檚 in some of these PODs, whether it鈥檚 at a big site,鈥� he said. 鈥淲e鈥檙e trying to make it so ubiquitous that essentially you fall into a vaccination needle without much effort.鈥�