Public health experts are preparing for a ‘twin anemia’ as autumn approached last year: a double threat from the coronavirus and the seasonal flu.
But even as cold, dry weather descended on the Northern Hemisphere and COVID-19 cases increased, the U.S. and the United Kingdom experienced historically mild flu seasons.
Between October 1 and January 30, only 155 Americans were admitted to the hospital with the flu, compared to 8,633 during about the same time period a year ago. This is a decrease of 98%. Labs in the US have collected and tested more than half a million flu samples since the end of September, but only 0.2% of the samples tested positive (a total of 1,300), according to the Centers for Disease Control and Prevention.
Every U.S. state experiences ‘minimal’ flu activity, the agency reports. This is in contrast to the previous season, when 22,000 Americans died of the flu.
A likely driver of the extraordinarily low infection and hospitalization rates is COVID-19. Measures to slow or prevent the spread of the coronavirus have also stopped other pathogens such as the flu, according to Sonja Olsen, a CDC epidemiologist at the National Center for Immunization and Respiratory Diseases.
“Measures, including extensive reductions in global travel, teleworking, school closure, social distance and the use of face masks, may have played a role,” she told Insider. Olsen noted, however, that it is challenging to pester exactly which of the measures are most important for influenza prevention.
“I do not think anyone expected a season where there was no flu”
Worldwide, according to the World Health Organization, influenza activity is at lower levels than expected for this time of year. Since the start of the pandemic, the Southern Hemisphere has ‘had virtually no flu circulation’, the CDC reported.
This is despite the increasing testing of flu in some countries, according to Olsen.
“There is some flu in tropical countries, but in these countries it seems that the season has blunted compared to other years,” she said.
David Battinelli, chief medical officer at Northwell Health and a professor of medicine at Hofstra University, told Insider that experts had always “hoped that social boundaries, masking and more hand hygiene would alleviate the flu.”
“But I don’t think anyone expected a season where there was no flu,” he said, adding, “no one has seen it on the entire planet.”
Flu season usually peaks in February, so most likely the US is clear, but Battinelli warned that it would be too early for a sigh of relief.
“Flu seasons can definitely last until March,” he said. According to the CDC, six flu seasons have peaked in the last 40 years.
Why coronavirus restrictions have worked so well against the flu
Influenza does not spread as well as the coronavirus. The average number of people infecting one person with the flu – a measure known as the reproductive rate – is 1.28. Usually someone who is sick with the coronavirus passes it on to between 2 and 2.5 people. In part, this difference is because the coronavirus can be in the air and hang in the air for hours. This does not apply to flu, although viruses can spread from person to person via respiratory droplets and infected surfaces.
The higher reproduction rate of the coronavirus “means that it is more difficult to prevent transmission through non-pharmaceutical interventions than for influenza,” Olsen said.
In addition, existing immunity in the population, whether against previous infections or vaccinations, can also increase the effects of social health measures such as masking, resulting in a more dramatic reduction in transmission, Olsen said.
The flu vaccine has been around for over 75 years. According to Olsen, vaccine manufacturers have predicted that they will supply up to 194 to 198 million doses of flu vaccine to the US.
“Compare that to a new coronavirus, to which almost the entire population is susceptible,” she said.
Research also shows that events in the superspreader – a condition in which one person infects an excessive amount of others – are the primary way the coronavirus spreads, unlike flu.
Reduced travel played a greater preventive role than flu shots
CDC data suggests that U.S. pharmacies and physicians’ offices administered more flu vaccines to Americans this season than in the previous year, when Americans received 174.5 million doses. The increase came after public health experts pressured people to get flu shots; some research has suggested that the chance of getting COVID-19 may be reduced.
But Olsen said the extra vaccinations are unlikely to be the reason for the low number of flu cases worldwide.
“While some places in the world use more vaccine, it is not generally true,” Olsen said. “We have seen less flu circulation, even in places that do not use vaccine, or use very little.”
However, both Olsen and Battinelli think that a decrease in travel played an important role.
“The traditional flu movement around the world has not taken place,” Battinelli said.
The flu is usually brought to the Northern Hemisphere in the autumn from the Southern Hemisphere, which has its flu season between April and September. But travel bans and limited air travel mostly halted the spread.
“We would expect flu to return sometime”
Experts do not think a non-existent flu season will occur regularly, and a study from Cambodia suggests that flu will start circulating if pandemic-related restrictions are lifted.
“We would expect flu to return at some point,” Olsen said.
Yet the rise of more transmissible coronavirus variants and the slow pace of global vaccinations could mean the pandemic will last until 2022, requiring another year of rigorous masking and social distance. If so, Battinelli thinks next year’s flu season will be just as mild.
For him, the take away from this unprecedented season is that Americans have the ability to actively curb flu transmission – and prevent tens of thousands of flu deaths – by hiding themselves, giving up social distance and practicing good hand hygiene.
“It’s a wake-up call that we should not tolerate so many deaths,” Battinelli said.
Read the original article on Business Insider