Is a 'twindemic' of Covid-19 and flu coming this autumn?

  • With autumn on the doorstep in the US, there is the possibility of two overlapping epidemics
  • A bad outbreak of 'regular' flu combined with an upsurge in Covid-19 could overwhelm health services
  • Getting the latest flu shot can reduce one's risk of at least one of the respiratory infections

Autumn is approaching, and so is the possibility of what public health officials are calling a "twindemic" – overlapping epidemics of both Covid-19 and influenza.

A bad flu season coupled with continued Covid-19 outbreaks could increase people's risk of fatal illness and overwhelm hospital capacity in communities already scrambling to treat coronavirus patients, experts say.

"I think it's definitely a possibility and it's something we're all worried about," said Dr Eric Cioe-Pena, director of global health at Northwell Health in New Hyde Park, New York. "The trifecta of a bad flu season, a bad Covid resurgence and an Atlantic hurricane is our doomsday scenario. You could add in civil unrest around the election as a four-way doomsday scenario."

Blunting the effect of one infection

The concern is so great that officials worldwide have been pressing for people to get this year's flu shot, even though it's only now hitting the market.

Getting your flu shot "could at least blunt the effect of one of those two potential respiratory infections", Dr Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, told The New York Times.

Fauci shared his thoughts on vaccination in this video:

The US Centers for Disease Control and Prevention usually purchases a half-million doses of flu vaccine for uninsured adults, but this year the agency increased its order by an additional 9.3 million doses, according to the Times.

But the protective strategies that officials have been promoting against Covid-19 – masking, hand-washing and physical distancing – should reduce the risk of a twindemic.

"The same things we do to prevent Covid should work for another virus called influenza," said Dr Waleed Javaid, director of infection prevention and control at Mount Sinai Downtown, in New York City. "If we follow the same recommendations, they should be effective for influenza and for Covid, and we might not see as much spread of influenza as we've seen in previous years."

Indeed, the Southern Hemisphere is in the middle of its flu season and has seen a dramatic decrease in flu cases thanks to protective measures adopted against the new coronavirus.

The Australian experience

"In Australia, the flu cases are down around 99% compared with last year," noted Dr Amesh Adalja, a senior scholar with the Johns Hopkins Center for Health Security, in Baltimore.

Unfortunately, the United States probably won't see this benefit because the nation has not fully embraced the recommended protections against Covid-19, Adalja continued.

"There is likely to be some effect, but the fact of the matter is even though we have all these measures for Covid, in the United States we haven't really been as adherent to them as in other countries. We have to prepare for the fact that we may not get the Australian experience of influenza," Adalja said.

A community facing a twindemic could soon find itself running out of hospital capacity, Adalja added.

'Back to back' cases

Last year's flu season was relatively mild, but still resulted in between 39 million and 56 million cases of flu, as many as 740 000 hospitalisations, and between 24 000 and 62 000 flu deaths, according to preliminary CDC estimates.

"You have to remember those viruses are going to compete for the same hospital beds, ICU beds, ventilators, personal protective equipment and even diagnostic test reagents," Adalja said.

Doctors are particularly worried about people who catch one of the viruses and then the other, back-to-back.

"I would say a sequential infection could be really a major problem for somebody, to get hit twice in a row. They might have sustained lung damage from Covid and now have to deal with influenza," Adalja said. "I would think the lung damage one would induce would make you more susceptible to a severe outcome with the other one."

Both infections at once

That's why public health officials are pressing for as many people as possible to get the flu shot, so they have some protection against at least one of these circulating viruses.

Cioe-Pena said, "We can't vaccine-prevent Covid, but we can vaccine-prevent flu visits to hospitals this year. I strongly encourage everyone to get their flu shot."

The flu vaccine contains particles of three to four different strains of flu that officials guess will be the ones most in circulation during the influenza season in any given year. Even if the vaccine is not an exact match to the flu that winds up being most common, it primes the body to produce an immune response that will limit the severity of a person's illness.

"People say I took it one year and I got the flu anyway," Cioe-Pena said. "What you will notice is there are very few people who say, 'My loved one or I got the flu shot and then I was on a ventilator with pneumonia.' Even when it doesn't prevent the illness, it is still the best tool we have at attenuating the effects of the flu."

In the most severe recent flu season, 2017-2018, the flu vaccine only had an overall estimated effectiveness of 38% across three strains, and was particularly weak against the H3N2 strain, the CDC reported.

Nonetheless, the CDC estimated that the imperfect vaccine still prevented 7.1 million illnesses, 3.7 million medical visits, 109 000 hospitalisations and 8 000 deaths that season.

Record number of shots

"It does prevent severe flu," Javaid said, "and that is going to be the critical element in this situation. I have seen people get flu and Covid back-to-back, and I can tell you that people who were vaccinated had much better outcomes."

During the six influenza seasons from 2010 through 2016, the flu vaccine prevented as many as 6.7 million cases of flu, 3.1 million doctor's visits, 87 000 hospitalisations and 10 000 deaths, the CDC said in its report on this year's flu vaccine.

Vaccine producers are preparing for a record 98 million flu shots to be handed out in the United States, about 15% more than last year, the Times reported.

However, Americans remain vaccine-hesitant. In the 2018–2019 flu season, only 45% of US adults got the vaccine, with rates particularly low among those aged 18 to 50, the Times noted.

"The best way to prevent this twindemic is to have as high a vaccination rate for influenza as we can, so there is room to take care of these Covid patients and we don't have to worry about dual infections or sequential infections," Adalja concluded.

Image credit: iStock

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