Atlanta, Georgia (CNN) -- As H1N1 cases are rising, so are bacterial pneumonia cases, health officials are finding.
They're seeing an increase in flu complications leading to pneumonia. At the same time, the flu is at record levels because of the new H1N1 virus, also known as swine flu.
The number of cases is outpacing the typical number of regular flu cases at this time of year. Cases of regular flu usually peak between December and May.
"We're seeing an increase in serious pneumococcal infectious around the country," said Dr. Anne Schuchat, who heads the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention.
The CDC tracks pneumococcal infections with help from 10 state health departments.
For instance, Denver, Colorado, averages about 20 cases of pneumonia in October during a regular flu season, Schuchat said. But "in October 2009, they had nearly triple that number."
The Denver area has seen 58 flu-related pneumonia cases, and at least two-thirds of those sickened were aged 20 to 60, she said.
During a regular flu season, most serious cases of flu and flu-related pneumonia occur in people 65 or older. However, people younger than 65 are much more vulnerable to H1N1, because the virus is unlike any other flu their bodies have come in contact with.
A flu infection thins the lining of the respiratory tract, making the lungs more vulnerable to bacteria that can cause pneumonia.
CDC officials are urging high-risk adults to get vaccinations against both pneumonia and H1N1.
Smokers and people with diabetes; chronic heart, lung and liver disease; or HIV are considered high-risk.
Only 25 percent of high-risk adults under age 65 have gotten a pneumonia vaccination, Schuchat said at a news briefing Wednesday.
"It's a vaccine you pretty much get once as an adult, not every year, the way the flu vaccine works," she said.
The CDC also announced that 7 million more doses of H1N1 vaccine have been made available since Friday, bringing the total doses available so far to 61.2 million.
CDC officials have studied safety data since H1N1 vaccinations started in early October.
"So far, everything we've seen is very reassuring," Schuchat said. " ... we're seeing patterns that are pretty much exactly what were seeing with the seasonal flu vaccine."
Most of the reported side effects include sore arms and tenderness at the injection site.
Health officials are particularly interested in a side effect that can cause a rare neurological illness called Guillain-Barre syndrome, because the last time a large-scale pandemic vaccination program was launched, in 1976, there was an alarming rise in Guillain-Barre cases.
This time, after millions of Americans have been vaccinated, Schuchat said, only 10 potential cases of Guillain-Barre have been reported, which is similar to what health officials see during a regular flu season.