Another record day for India, with more than 97,500 new Covid-19 cases in 24 hours

Samaypur Badli and Huda City Centre on the first day of its reopening after five months of Covid-19 lockdown. Naveen Sharma/Sipa via AP Images

Delhi's subway system resumed full operations Saturday with the reopening of its Airport Express Line, which closed in March amid the Covid-19 pandemic.

Over the past week, the Delhi Metro Rail Corporation (DMRC) has gradually reopened all tracks in the Indian capital, keeping certain restrictions in place.

With India still setting new global highs of daily coronavirus cases, stations in containment zones will remain shut.

More than 1,000 officials have been deployed across stations to ensure smooth movement under existing restrictions. A limited number of passengers will be allowed to board each train to prevent overcrowding, and all ticket transactions will be cashless, the DMRC said.

Only asymptomatic passengers will be allowed to travel in the trains and face masks are mandatory, according to a press release issued by the Ministry of Housing and Urban Affairs.

The capital is one of the few cities in India which has reopened its public transportation. In Mumbai, the Maharashtra government stated that subway services will continue to remain suspended.

India is the second-worst hit country in the world in terms of total coronavirus cases, behind only the United States.

Health care workers during a covid-19 screening and swab test at on September 10, in Mumbai, India. Satyabrata Tripathy/Hindustan Times via Getty Images

India reported 97,570 new coronavirus cases Saturday, according to the Ministry of Health and Family Welfare -- the third day in a row the country has set a global record for daily infections.

India's total number of confirmed cases stands at 4.65 million, of which about 958,316 are active. The total number of recovered patients stands at more than 3.6 million.

The nationwide death toll is 77,472, according to the health ministry.

The ministry also reported 1,091,251 Covid-19 tests were performed Friday, bringing the country's total number of tests to 55,189,226.

India is the second-worst hit country in terms of total cases, behind only the United States.

President Donald Trump's lawyer and former New York City mayor Rudy Giuliani talks to journalists outside the White House on July 1, in Washington, DC. Chip Somodevilla/Getty Images

Former mayor Rudy Giuliani has criticized the current New York City leadership, saying they're "killing this city" with continued Covid-19 restrictions.

"I wouldn't do what they are doing now," he told CNN's Chris Cuomo Friday night. "I wouldn't keep this city closed as long as they are keeping it closed. I think they are killing the city... I think what they are doing to this city could be fatal."

"They are overdoing," he added. "They are killing the city."

Giuliani's remarks come as movie theaters, amusement parks and casinos remain closed and indoor dining banned, among other restrictions.

This illustration, created at the Centers for Disease Control and Prevention (CDC), reveals ultrastructural morphology exhibited by coronaviruses.  Centers for Disease Control and Prevention (CDC)

As doctors worry about a coronavirus-and-flu "twin-demic" that could overwhelm the health care system, Americans must contend with another possibility: fighting both viruses at the same time.

"You can certainly get both the flu and Covid-19 at the same time, which could be catastrophic to your immune system," said Dr. Adrian Burrowes, a family medicine physician in Florida.

In fact, getting infected with one can make you more vulnerable to getting sick with the other, epidemiologist Dr. Seema Yasmin said.

"Once you get infected with the flu and some other respiratory viruses, it weakens your body," said Yasmin, director of the Stanford Health Communication Initiative.

"Your defenses go down, and it makes you vulnerable to getting a second infection on top of that."

On their own, both Covid-19 and the flu can attack the lungs, potentially causing pneumonia, fluid in the lungs or respiratory failure, the Centers for Disease Control and Prevention said.

Each illness can also cause sepsis, cardiac injury and inflammation of the heart, brain or muscle tissues.

Having both illness simultaneously "would increase the risk of longer-term effects of any of those organ systems," said Dr. Michael Matthay, a professor of medicine and a critical care specialist at the University of California, San Francisco.

Read more here.

Fog and smoke looms over the Lawrence Berkeley National Laboratory in Berkeley, California, on September 9. Paul Chinn/The San Francisco Chronicle/Getty Images

Amid rapidly spreading fires across California and other western parts of the United States, several medical professionals are warning unhealthy air quality from wildfire smoke can make people more susceptible to Covid-19 and worsen existing infections.

Higher amounts of air pollution and smoke particles in the air could also predispose people to being more susceptible to acquiring and having more severe Covid-19 disease, Spellberg said, citing several studies conducted in the US, China and Italy.

Dr. Rekha Murthy, an infectious disease specialist and vice president of medical affairs at Cedars-Sinai Hospital in Los Angeles, said smoke from wildfires can irritate the lungs and can cause inflammation that can affect the immune system. That inflammation can make people more likely to experience lung infections, including from viruses like the one that causes Covid-19.

"Whenever the lining of the lung or the airways become inflamed or damaged, it increases the potential for inhaled viral particles to take hold in the lungs and cause infection," Murthy said.

CNN Medical Analyst and ER physician Dr. Leana Wen also agreed air pollution increases the likelihood of respiratory illnesses -- and those illnesses can make vulnerable populations experience more severe effects from Covid-19. Wen said there are also legitimate short-term concerns that the smoke-filled air will likely drive more coronavirus-positive people indoors, which could also potentially lead to a rise in the spread of the virus.

To prevent the possible spread of Covid-19 during the unprecedented overlapping of an intense fire season during a pandemic, Wen recommends that all individuals who are remaining indoors due to poor air quality should also stay away from anyone who is not in their immediate household.

Murthy, of Cedars-Sinai Hospital, also recommends the best way to protect yourself and others against Covid-19 during the wildfire season is to reduce any possible exposure to smoke by seeking clean air spaces and limiting outdoor exercise.

Brazil’s health ministry reported 874 new Covid-19 deaths on Friday, raising the country’s death toll to 130,396.

The ministry also reported 43,718 more coronavirus cases, with the nationwide total now at 4,282,164.

According to a tally by Johns Hopkins University, Brazil is the third-worst hit country in the world in terms of cases, behind only India and the United States. It is second-worst in terms of deaths, with only the US having suffered more coronavirus fatalities so far.

A worker transports the body of a Covid-19 victim to be cremated at the San Isidro Crematorium on July 15 in Mexico City. Hector Vivas/Getty Images

Mexico’s health ministry reported 534 new Covid-19 deaths on Friday, raising the country’s death toll to 70,183 -- the fourth-highest in the world, behind only India, Brazil and the United States.

The ministry also reported 5,935 new Covid-19 cases, taking the nationwide total to 658,299.

Despite its struggles with the virus, Mexico is still welcoming international tourists, including from the US, as the economy struggles under the weight of lost revenue.