It's been almost four years since COVID hit. Since then, doctors have seen new variants and even new respiratory viruses. Doctors say they are now seeing new co-infections.

That sneeze could be COVID, the flu or RSV. Dr. Onyema Ogbuagu at the Yale School of Medicine says all three are now circulating at the same time, and we are seeing a peak in cases. He says he is seeing co-infections - but not all three at the same time.

"But we are seeing people having at least two at the same time.  You know COVID and influenza or COVID and RSV tends to be the more common combinations," said Ogbuagu.

Ogbuagu says cases seem to be affecting the same types of patients.

"For RSV specifically, we are seeing more older people as well as younger patients ... it hits people at two different life spans if you will," says Ogbuagu.

Doctors say those most at risk are people who have underlying respiratory conditions like COPD or asthma and also people who have heart disease. Ogbuagu says the vaccines for COVID and the flu are controlling the severity of cases. He says Pfizer now has a new RSV vaccine.

"The Pfizer vaccine is also approved for use by women in late pregnancy to protect their newborns against having RSV," says Ogbuagu.

Ogbuagu says he is not ready to call COVID a seasonal virus because it is now happening all year long.

Doctors say we still seem to be on track to have a single vaccine to fight COVID and the flu by later this year.