Doctors are yet again warning over the threat of a possible "twindemic," or burdened hospitals amid converging respiratory illnesses like COVID-19 and influenza, prompting calls to receive flu shots early.

Experts had issued a similar warning last summer amid soaring COVID-19 infections, citing worries over overwhelmed hospital systems by both COVID-19 and the influx of flu patients, but the surge never came. From October to mid-February, the Centers for Disease Control and Prevention (CDC) recorded 165-laboratory confirmed flu-related hospitalizations in the U.S., the lowest rate of flu-related hospitalizations since data collection began in 2005.

However doctors' warnings have resurfaced, with experts citing social mixing and relaxed mitigation measures as the country approaches the colder seasons.

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"This year, however, we are heading into the flu season with more relaxed restrictions and the situation will allow for increased chance of respiratory illness transmissions," Dr. TingTing Wong, internist and infectious disease specialist at NewYork-Presbyterian Medical Group Brooklyn, told Fox News. "We saw a similar uptick of 'summer colds' caused by other viruses (for example RSV, respiratory syncytial virus, and rhino viruses, etc.) this summer as restrictions relaxed and the fear is a similar uptick of flu cases this fall/winter season."

"Bottom line, please get the flu vaccine early!" Wong added.

National reports of RSV, a common respiratory virus, increased into July, nearly hitting highs not seen since late fall to winter of 2019, according to laboratory data submitted to the Centers for Disease Control and Prevention (CDC). RSV infections typically occur during the fall, winter and spring, suggesting an unusual summertime uptick coinciding with rising cases of the delta variant. However, data indicates PCR detected RSV cases began to decline later into July, per the latest complete data.

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COVID-19 cases are also increasing; at the latest White House COVID-19 response briefing, Dr. Rochelle Walensky, CDC director, noted that the seven-day average of new daily cases and deaths are increasing, with about 137,000 new cases per day, or a 12% rise from the prior seven-day period, and about 739 deaths per day, or a 23% increase over the prior week. The seven-day average for hospitalizations was similar to the prior week at around 11,000 per day.

However, flu circulation remains low, added Dr. Ravina Kullar, infectious diseases specialist, epidemiologist and adjunct faculty at David Geffen School of Medicine at UCLA.

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"With COVID-19 infections surging in the United States, other respiratory pathogens have been unseasonally increasing as well, particularly RSV and parainfluenza. To date, we have not seen a high prevalence of flu cases. According to the CDC influenza surveillance, flu circulation remains low at around 2.1%, which is below the baseline of 2.6% nationally."

Kullar warned the flu circulation rate "could change at any point" amid social mixing and relaxed mitigation measures, such as facemasks.

"It is important to get your flu vaccine now," she stressed.

Fox News' Alexandria Hein contributed to this report.