Marin is nearing herd immunity as vaccination rates soar among the highest in the nation and case rates sink to their lowest levels in a year. 

The county is seeing fewer than four cases a day, and only one death has been reported since April 17. On Tuesday, the state moved Marin into the least restrictive tier of reopening, allowing bars to open and indoor capacity to expand. All Covid-19 restrictions, including the mask mandate, are set to lift on June 15, except for at large events and in certain workplaces.

The Old Western Saloon opened on Tuesday after a 14-month closure. “We are so, so excited,” said Michelle Pelton, a part owner. “It’s been a long haul watching all the other businesses open up.”

Brittany Hartwell, the manager at the Palace Market, said the grocery will follow state guidance in lifting its mask requirement in two weeks.

If Marin can vaccinate eight out of 10 residents, ongoing chains of transmission will die out, said Dr. Matt Willis, Marin’s public health officer. The virus could jump to one new host in the 10 or so days that it is capable of spreading, but a second infection would be highly improbable. The county is on pace to meet that goal: Sixty-three percent of Marin residents are fully vaccinated, and another 14 percent are partially immunized.

“We are not going to eradicate Covid-19, but we will suppress its local transmission so much that we’ll be protected as a whole,” Dr. Willis said.

Still, vaccine opponents have flooded the Board of Supervisors with calls after the Pfizer vaccine was approved for adolescents. Some were anti-vaxxers who pushed conspiracy theories, comparing the vaccine to the Holocaust and calling it a crime against humanity. They ranted about Bill Gates, and said the pandemic was an emergency created by the government. 

Others were more level-headed, highlighting the zero deaths in children in Marin and pointing out that the vaccine is only authorized for emergency use. They said limiting activities for unvaccinated children is discriminatory and damaging to their kids. 

“If you tell a kid that he can’t be in a sport or part of a club or go to the prom unless he or she is vaccinated, that’s not free choice,” lawyer Andrew Kislik said. “And if you tell a kid or a parent that this is safe and effective and that there’s no adverse effects, that’s not informed consent. In fact, some would call that lying.”

Schools currently have no Covid-19 vaccine requirements, although public health officials have raised the possibility for a mandate after the vaccine is approved for regular use, and only if the lack of vaccinations is causing surges. 

Pfizer’s trials on children younger than 12 are underway. In the company’s study of 2,260 adolescents between age 12 and 15, there were 18 cases in the placebo group, and zero infections in the vaccinated group. Marin has given the first dose to 70 percent of the roughly 12,000 people in this group.

Vaccine safety is monitored on a national scale using the Vaccine Adverse Event Reporting System, or VAERS. Over 285 million doses of the Pfizer, Moderna and Johnson & Johnson vaccine have been administered in the United States, and VAERS has received 4,863 reports of death. Anyone can make a report to VAERS, and physicians review each case using clinical information, death certificates, autopsies and medical records. 

The only deaths believed to be caused by a vaccine were a result of the Johnson & Johnson vaccine that was paused in April after VAERS detected cases of serious blood clots. Over 10 million doses of that vaccine were given in the United States, and monitoring confirmed 32 instances of people who later developed a serious blood clotting condition. At least three people died, according to the Centers for Disease Control and Prevention. The vaccine resumed after three weeks because data showed its benefits outweigh its risks. However, the C.D.C. warns women younger than 50 years old that the Johnson & Johnson vaccine carries increased risk for them.

Dr. Willis explained that no pharmaceutical product has zero risk; even ibuprofen has side effects. The expectation that a biologically active product would never lead to an adverse reaction is unrealistic and unwise, he said. 

He also cautioned against confusing correlation with causation. Every year, around 2,000 people die in Marin, so naturally, people will die, have strokes and go into cardiac arrest after getting the vaccine.

“The process is really: What is the expected background incident of any condition or any outcome? And is it higher among people who are vaccinated? And that’s where we need to look at the data,” he said. 

People who are opposed to the vaccine often share social groups or schools. If all the unvaccinated people were randomly distributed throughout the county, transmission would be rare. But vaccine-hesitant people are often like-minded, socially connected and therefore more susceptible to spreading the virus. Outbreaks of measles have been seen in Marin among groups with shared beliefs around vaccination, Dr. Willis said.

Roughly 93 percent of Marin’s Covid-19 cases since March 1 affected people who were not fully vaccinated; the rest were “breakthrough cases,” which are less likely to lead to hospitalization and death. The lone death last month was an older resident who was living independently and was not vaccinated. The source of infection was not determined. 

Marin’s public health goal is to remove barriers to the vaccine. Some barriers pertain to access, whether it’s a lack of transportation, poor internet or language. Mobile clinics are touring the county with teams of bilingual health educators to meet people where they are at. Other barriers arise from a lack of trust, knowledge or understanding of the science. These psychological barriers are best addressed through one-on-one conversations with personal doctors.

California is making its push with financial incentives, giving out 10 prizes of $1.5 million, 30 prizes of $50,000 and two million $50 grocery cards to people who get vaccinated.

To reach the state’s yellow tier of reopening, the county needed an adjusted case rate below two cases per 100,000 residents for two consecutive weeks. Marin has toed the line for the past eight weeks, often having one week below two cases and the next above. Finally, the county earned the two consecutive weeks on Tuesday. Gyms, restaurants, churches and movie theaters can expand their indoor capacity, and if patrons show proof of vaccination or a negative Covid-19 test, capacity limits are higher.