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COVID-19 precautions may reduce cases of influenza and other respiratory infections


Heading into winter, doctors and scientists have noticed something strange: cases of non-COVID-19 respiratory diseases are missing, especially the flu and respiratory syncytial virus or RSV.

“We’re seeing a very low number of these infections, even now, while we’re in the high season,” says Rachel Baker, an epidemiologist at Princeton University. "We should really see how the cases increase."

In contrast, positive flu tests reported in December are just under one-hundredth of those counted in December 2019, according to data from the U.S. Centers for Disease Control and Prevention. The fall in RSV in reported cases, up to two hundred of which a year earlier, is even greater.

This dramatic dive is probably due to the precautions of COVID-19. The same hand washing and social distancing that can prevent the spread of SARS-CoV-2, the virus that causes COVID-19, can prevent the spread of other viruses and pathogens. But that can mean problems ahead. Lack of cases ironically leads to a growing population susceptible to infection, so future outbreaks may be larger and more unpredictable.

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In a typical U.S. year, RSV hospitalizes approximately 58,000 children under the age of 5 and more than 177,000 older adults. “Most people recover in a week or two,” says Benjamin Silk, a CDC epidemiologist. "But RSV infections can be serious, especially for babies, older adults, and people with certain chronic illnesses." Worldwide, 3.4 million children under the age of 5 are hospitalized with RSV each year, accounting for approximately 5 percent of deaths in this age group.

Highly contagious, RSV is transmitted through respiratory droplets, which can remain infectious for more than six hours on hard surfaces. Prevention is rooted in strict hand hygiene: use hand sanitizer or wash with soap and water.

In the United States, the RSV season usually begins in the fall, peaking between December and mid-February. This year, essentially, there is no peak. As of December 2020, the CDC’s national respiratory and enteric surveillance system (which collects voluntarily reported data) reported only 120 cases of RSV, compared to December 24,280, 2019.

“The RSV, in particular, is so stable: it does the same thing year after year,” Baker says. "I don't think there's much more that can explain (the fall) besides COVID-19 phenomena as a whole, particularly control measures."

Influenza infections also drop drastically. The flu regularly infects between 3 and 11 percent of the U.S. population and is especially fatal for the elderly or immunocompromised. The CDC estimates that in an average year the flu kills about 36,000 people and hospitalizes nearly half a million.

According to CDC's leading flu tracker Lynnette Brammer, the adoption of COVID-19 prevention measures in the spring of 2020 coincided with a drop in the percentage of positive flu tests from more than 20 percent to less than 1 percent, and that number remained low during the fall and now in the winter (SN: 18/09/20). In December 2019, the CDC’s FluVue clinical lab reported 50,526 positive flu tests. In December 2020, that number was 454. Preliminary data suggest that this trend continues until January, when the flu season usually peaks.

Brammer says the number of flu tests is constant, so it’s not that people don’t get tested. They just don’t extend it that much.

Some other infections, such as parainfluenza, also appear to have decreased with COVID-19 prevention measures, but viruses such as rhinoviruses remain close to their normal seasonal levels. It could be because these viruses, unlike the flu and RSV, are not destroyed as well by hand washing and the use of disinfectants.

This great news comes with a warning. Fewer infections mean fewer people are exposed and get immunity to these viruses, forming a population susceptible to these infections later. This could fuel a deadly rebound in infections after COVID-19, Baker, the Princeton epidemiologist, and colleagues reported on Dec. 1 in Proceedings of the National Academy of Sciences. In the analysis, the team assumed that COVID-19 precautions would reduce RSV and influenza infections by 20 percent, but the decrease is being much greater.

“We need to be prepared for low-season shoots and potentially large shoots,” says Baker.

That’s what’s happening right now in New South Wales Australia. Clinical nurse Gemma Saravanos and colleagues observed a more than 85 percent reduction in positive RSV tests during the peak of their season, between April and June, the team reported in the Lancet in September. But now, after defeating COVID-19 and lifting strict protection measures, they have a record-breaking RSV outbreak in their hands. In the last two weeks of December 2020, NSW reported more than 6,000 positive RSV tests; for a time they usually have a few hundred. In 2019, the RSV season peaked at 4,695 detections in May.

“It’s really extraordinarily unusual,” says Saravanos, who works at the University of Sydney. "Never seen before."

A rebound outbreak could also hit the United States, Baker says. Australia "could be an interesting omen of what will come in the northern hemisphere."

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That worries Carla Burroughs, a mother of four and a former doctor in Mobile, Alabama, who experienced RSV first-hand. “The first time I heard of RSV, I was working in an ambulance and I (transported) a child who passed away (from her),” she says. Then, in December 2019, Burroughs ’daughter Kaylee, 3, caught RSV and was hospitalized for three days. "The second the doctor told us RSV with Kaylee, he just brought flashbacks. He just sent me into a panic mode; I immediately knew this was going to be bad."

He did wrong. A week later, the Burroughs infantry twins caught RSV. One of them, Mackenzie, was intubated for two weeks and was in the hospital for more than a month. Seeing his daughter struggling to breathe, Boroughs says, "It just changed everything. It took me more toll than I expected."

Burroughs children have recovered and says new data now shows how important basic hygiene behaviors are to help prevent the spread of these viruses, saving thousands of lives every RSV and flu season, even without a pandemic. “It’s sad that (the pandemic) is what happened,” Burroughs says. "We should already be doing all these things."

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