Vaccinations are available at Cambridge health department offices in The Port neighborhood. (Photo: Marc Levy)

The city’s health department and doctors and pharmacies at the Cambridge Health Alliance are prepared to offer extra Covid-19 booster shots to older people and those who are immunocompromised, representatives said last week. Federal authorities on Wednesday recommended another booster for people over 65 if their previous vaccination was more than four months ago and for people with weakened immune systems whose previous vaccination more than two months ago.

Both health care organizations have enough supply of the bivalent boosters, designed to protect people against the original Covid-19 virus as well as versions of the newer Omicron variant, spokespersons said. The new recommendation “will not have a material impact on our vaccination effort,” said Dawn Baxter at the Cambridge Public Health Department. CHA spokesperson David Cecere said the Alliance has “a sufficient supply of the bivalent vaccine.”

The health department offers vaccinations by appointment on Wednesdays at its office at 119 Windsor St. and CHA provides shots for its patients at doctor’s offices and for the public at outpatient pharmacies at Cambridge Hospital and the East Cambridge clinic at 163 Gore St.

As the new recommendations go into effect, fewer than half of Cambridge residents have received a shot of the bivalent booster, according to the most recent figures from the state Department of Public Health on April 17. The state agency is estimating bivalent booster uptake by singling out the number of people boosted after Sept. 1, 2022, when the bivalent shot was virtually the only type of booster administered. In Cambridge, about 44 percent of residents got a booster after that date.

Breaking down the vaccination data by age, state figures show that about 75 percent of residents over 65 – who are considered more at risk from Covid – have already received a  bivalent shot. When it comes to older people who got at least one Covid shot of any kind, though, or who received the two primary vaccinations that formerly identified them as fully vaccinated, the state figures are confusing: They show more people vaccinated than the total number in that age group.

The state reported that 16,387 Cambridge residents 65 and older have received at least one shot and 15,018 are fully vaccinated with two primary shots – compared with the city’s total over-65 population of 13,459.

The state explained in notes with its weekly vaccination reports that this might happen because a person’s age is calculated as of the date of each report. Baxter at the Cambridge Public Health Department provided this example: “A person born in October 1993 is 29 years old. If they receive a booster today, they are counted in the 20-29-year-old category. However, in October they will be counted in the 30-39-year-old category.” This could lead to more and more people falling into older age categories as the pandemic reporting continues.

Despite the apparent discrepancies, Baxter said: “We believe these are reasonable estimates of the vaccination rates in the city.” She also pointed out that the age group population totals that figure into calculating the percentage of people vaccinated are actually estimates from the 2020 Census, not hard and fast numbers. “Therefore, if population estimates are lower than the total number of people vaccinated, we might say: ‘more than 95 percent of people in X age category are vaccinated,’” Baxter said.

That actually occurs in vaccination reports for the entire Cambridge population. The April 17 state figures for Cambridge show that 125,523 residents have received at least one shot, while the total city population is 118,403. The state says more than 100 percent of residents have at least one shot, while the city says it’s more than 99 percent. Whichever figure you use, virtually all residents have received at least one shot.

The city stopped posting weekly vaccination reports in its Covid data center this month because the state – the source for the city reports –- changed the way it reports booster shots, Baxter said. She said people who want to see the weekly Cambridge figures can get them on the state health department Covid website.

Meanwhile, federal authorities have not told state and local health officials what to do with stocks of monovalent Covid vaccine that is no longer approved. When the federal government recommended an extra bivalent booster for older people and those who are immunocompromised, it also decided that the bivalent shot would be the only approved vaccine for everyone 6 months or older. The Food and Drug Administration removed approvals for the previous Moderna and Pfizer vaccines.

Baxter said the change wouldn’t create a problem because the health department keeps “a very limited supply” of vaccine on hand.