If there were a prize given to the first Midpeninsula ZIP code to reach 100% vaccination for COVID-19, it may soon go to 94304, the Palo Alto Hills and Stanford West areas where it appears that everyone 12 years old or older has been either fully or partially vaccinated, according to California Public Department of Health data. The 12-and-over population, estimated at 3,264 by the state Department of Finance, is 86% fully vaccinated, with everyone else having already received one dose.

As Santa Clara County moved into the least-restrictive reopening phase this week, following San Mateo County's move to the same yellow tier last week, county Health Officer Dr. Sara Cody said she is encouraged about the massive effort to protect the local population from COVID-19 through vaccinations.

"For the first time, I feel optimistic. For a while, it seemed uncertain to me whether the vaccines or the variants would win. And now it looks like 'Team Vaccine' will come out on top," she said during a press conference on Tuesday.

In all but two ZIP codes of the Midpeninsula area stretching from north Sunnyvale to south Redwood City, two-thirds of residents ages 12 and over are partially or completely inoculated. In concrete numbers, that's 219,000 out of 361,000 people who've received a shot.

The Palo Alto Hills/Stanford West ZIP's through-the-roof vaccination rate may be helped by its small population, but size isn't necessarily an indicator: A dozen miles to the west, the ZIP code of 94020 in the Santa Cruz Mountains has among the lowest vaccination rates: 61.2%. Identified as the La Honda ZIP code, slightly fewer than half of its 1,580 residents aged 12 and older are fully vaccinated. (Only the Stanford ZIP code, 94305, has a lower rate; but the university has been mostly shut down for the past year and its population has a higher percentage of transient residents.)

Some of the Midpeninsula's most populated areas are also trailing somewhat in vaccinations. Among the ZIP codes with the lowest rates:

• 94303, with more than 40,000 residents in East Palo Alto and a portion of Palo Alto, has a rate of 69.1% of fully and partially inoculated residents.

• 94061, with more than 33,000 in the Redwood City and Woodside ZIP code that crosses State Route 84, has a rate of 67.1%.

• 94063, where more than 29,000 people live in the Redwood City and North Fair Oaks area, east of Middlefield Road, has a rate of 68.4%.

The North Fair Oaks ZIP code, however, is also among several where residents have been jumping on the vaccination bandwagon in greater numbers recently.

The percentage of North Fair Oaks residents who are in the midst of the immunization process is 18.1%; compare that to the majority of Midpeninsula ZIP codes, whose partial vaccination rates are between 13% and 16%.

This could be due to the fact that North Fair Oaks has a younger demographic, and thus more residents had to wait until they were eligible for a shot. The median age of 94063 is 33.1 years, according to the 2020 American Community Survey.

It could also be attributed to recent pushes by the county to get more people vaccinated in lower income areas through pop-up clinics.

Other ZIP codes with vaccination momentum are the 94085 area of north Sunnyvale, where the median age is just 32.6 years. It has the highest percentage of residents midway through the vaccinations: 18.7%.

And 94040, central Mountain View's ZIP code, has a partial immunization rate of 18% and a median resident age of 34.6 years.

The Palo Alto Hills neighborhood is not the only ZIP code to be sailing toward fully immunization. In Los Altos' 94022, which straddles Interstate Highway 280 and stretches east to El Camino Real, 91.7% of its 16,763 residents are either fully or partially vaccinated.

Also doing well: 94024, the Los Altos ZIP code that stretches from west of 280 to east of Foothill Expressway, where 86.8% have received at least one shot; and 94301, the Palo Alto area that includes the neighborhoods of Crescent Park, the downtown area and Old Palo Alto. There, 86.6% are either completely or halfway through the process.

Mark Nadim, a longtime resident of Palo Alto Hills, said that he is proud to live in a neighborhood that's achieved full vaccination.

"As to why we have such a high vaccination rate, it might be that with a small neighborhood with mostly high-tech residents as well as many seniors, we tend to be less suspicious of new technologies, whether they are pharmaceutical or otherwise," Nadim wrote in an email.

The state's data does not include persons immunized through the Veterans Health Administration, which received its doses directly from the federal government. In addition, the population numbers from the Department of Finance are projections and may not be completely accurate, according to the Department of Public Health's vaccination rate website.

Find comprehensive coverage on the Midpeninsula's response to the new coronavirus by Palo Alto Online, the Mountain View Voice and the Almanac here.