The proportion of COVID-19 infections and hospitalizations among vaccinated Pennsylvania residents rose sharply last month, though the shot remained broadly protective, according to new statewide health data released Friday.

The latest Department of Health data on “breakthrough” infections shows that between Sept. 5 and Oct. 4, vaccinated people represented 26% of more than 135,000 new infections and nearly 5,000 hospital admissions in the state.

Death statistics for the last 30 days were not available, because of lags in reporting and verification.

When the Health Department released its initial set of data on breakthrough cases on Sept. 14, just 6% of cases and 5% of hospitalizations since January were among vaccinated residents.

State health officials attributed COVID-19’s increased impact on vaccinated people to the rise of the highly transmissible delta variant of the coronavirus, along with waning immunity among some populations that have received the vaccine, among other factors.

“The vaccines were designed to prevent severe illness and hospitalization, but no vaccine is 100%,” the state’s acting physician general, Dr. Denise Johnson, said in a phone interview. “As we have more people vaccinated, there will be more cases in those vaccinated people. It doesn’t mean the vaccines aren’t working. They’re working as designed.”

She said the data reinforced the case for booster shots.

Last month, U.S. health officials approved a third dose of the Pfizer vaccine for all Americans 65 and older, along with higher-risk younger people.

“We know that the vaccines do give a great measure of protection,” Johnson said. “Even now, with the delta variant, with the waning immunity, the cases that we have, the hospitalizations that we have, people who are really ill, are still largely the unvaccinated.”

On Tuesday, Commonwealth Partners, a free-market advocacy association based in Harrisburg, released weekly Health Department data that it obtained through an open-records request that showed similar increases in cases and hospitalizations among vaccinated people - along with rising deaths.

Those statistics covered a period between late April and late August and showed the spikes were particularly pronounced after delta became the dominant strain of the virus. About a third of the state’s deaths from early July to mid-August were among vaccinated residents.

“In September, (the Health Department) had to know that the current numbers were different from what they were releasing,” said Gina Diorio, the group’s public affairs director.

Over the last month and since the beginning of 2021, the state’s data indicates that Pennsylvania’s unvaccinated residents were far more likely to contract COVID-19, become hospitalized and die than those who got the shot.

Last month, even as the state was in the grips of delta, unvaccinated people had triple the risk of being infected and landing in the hospital, the numbers show.

Since January, the risk of death was six times as great among unvaccinated residents. At least 518 vaccinated residents have died, about 7% of the 2021 total.