How Experts See This COVID and Flu Season Unfolding

Sept. 30, 2024 – What’s the outlook for COVID-19 and flu this fall and winter? It’ll probably be a lot like last year, experts say. 

“We currently expect this flu season to be comparable to last year’s season,” said Adrienne Keen, PhD, of the CDC’s Center for Forecasting and Outbreak Analytics. “We expect this year’ s COVID-19 season peak to be similar to last year’s or lower.” The CDC is still analyzing COVID surveillance data from the summer and will update the forecast as more is learned.

For COVID, that means it won’t be as bad as the pandemic years, and for the flu, it’s a typical pre-pandemic season. But status quo does not mean great. 

Between October 2023 and April 2024, as many as 75 million people got the flu in the U.S., according to CDC estimates, resulting in up to 900,000 hospitalizations and between 17,000 and 100,000 deaths. In 2023, about 900,000 Americans were hospitalized with COVID and 75,000 died.

Other experts agreed with Keen’s prediction. 

But unknowns – such as a COVID variant that takes off quickly or a surprise influenza strain – could knock that forecast flat. Getting vaccinated remains crucial, public health officials stress. 

Predicting COVID

Two key predictors of how bad an upcoming COVID season will be are the cycling of new variants and the population’s immunity (protection from an infectious disease that happens when a population is immune through vaccination or previous infection). 

When new variants go up and immunity goes down, “we tend to see the increase in cases,” said Michael T. Osterholm, PhD, MPH, director of the Center for Infectious Disease Research and Policy and a professor of public health at the University of Minnesota, Minneapolis. But if the number of variants goes down and immunity levels go up, the outlook is more favorable.

The new COVID variant called XEC has been found in at least 25 states. On Friday, the CDC added the variant to the COVID tracker. It now accounts for 6% of U.S. cases. This was expected, as the variant has been circulating in Europe, said Amesh Adalja, MD, a senior scholar and infectious disease expert at the Center for Health Security at Johns Hopkins University, Baltimore. 

“There will always be a new variant appearing, and one falling,” he said. “So the fact that this is happening is not surprising.” 

Meanwhile, the summer COVID surge has provided post-infection immunity for some people. “What’s likely is, we are going to see substantial protection of the population for several months based on previous infection and in some cases vaccination,” Osterholm said. That means protection from serious illness, hospitalizations, and deaths (but not necessarily infection). That protection could last through the year or into early next year, he said.

The timing of this year’s winter surge will likely be a bit later than last year’s, said Andrew Pekosz, PhD, a professor and vice chair of molecular microbiology and immunology at Johns Hopkins University, Baltimore, “peaking just after the Christmas/New Year holiday.”

Last year, weekly COVID hospitalizations peaked the week of Dec. 30, said Justin Lessler, PhD, a professor of epidemiology at the University of North Carolina at Chapel Hill and a member of the COVID-19 Scenario Modeling Hub.

But variants are unpredictable. “There’s a chance that the XEC variant may take off and spread, or might not,” said Adalja. As of Sept. 28, the Omicron variant KP.3.1.1 was leading, accounting for 58.7% of U.S. cases, according to the CDC.

While Adalja agreed that this year’s COVID season will probably be like last year’s, “we have to be prepared for cases and hospitalizations going up,” he said, “but not to the point of a crisis.” A return to lockdowns and social distancing is unlikely, he said.

Still, older adults and others at higher risk of getting very sick from COVID should consider masking during travel, said Rajendram Rajnarayanan, PhD, MSc, an associate professor at the New York Institute of Technology College of Osteopathic Medicine at Arkansas State University, Jonesboro.

Flu Forecasts

Predicting flu season this early is hard, said Jeffrey Shaman, PhD, a professor of environmental health sciences and professor of climate at Colombia University, New York.

“You can look at the CDC forecast and use it as a very loose guide right now,” said Shaman, who won the CDC’s first “Predict the Influenza Season Challenge” in 2014. “Until there is actually flu, it’s like trying to predict the landfall of a hurricane.” Flu activity remained low as of Sept. 14 (the most current data available), according to the CDC.

When flu activity picks up, typically in mid-October or November, experts look at the dominant strain, exposure to similar strains in previous years, and how well-matched the current flu vaccine is to that dominant strain, Shaman said. Vaccine makers must make an educated guess months in advance regarding which strain to target, to allow time for production.

The vaccination rate plays a role, too, but that tends to remain constant, Shaman said. According to the CDC, less than half of adults age 18 and up got a flu vaccination last year.

Experts also consider flu patterns in the Southern Hemisphere, where 2024 flu activity has mostly involved two subtypes of influenza A – H1N1 and H3N2 – and some influenza B, the CDC found.

How Well Do This Year’s Vaccines and Viruses Match Up?

The FDA has authorized three updated COVID vaccines for this fall. Novavax targets the JN.1 strain of SARS-CoV-2, the virus that causes COVID-19. Both mRNA vaccines, Moderna and Pfizer, target KP.2, a descendant of JN.1. All three target current predominant variants, and any one of them is recommended by the CDC.

The vaccines are a good “though not perfect match to virtually all the circulating variants of SARS-CoV-2,” said Pekosz.

Experts said that the shots will protect against the XEC variant. 

“XEC and its sub-lineages are expected to be the dominant fall/winter variant group,” said Rajnarayanan. 

This year’s flu vaccines, all trivalent (protecting against three viruses), will target the three strains expected to circulate – H1N1, H3N2, and influenza B (Victoria), according to the CDC.

People should still get vaccinated, Adalja said, and use home tests for flu and COVID and take antivirals promptly when needed. The goal should not be status quo but rather fewer COVID and flu hospitalizations and deaths, he said. 

SOURCES: 

Adrienne Keen, PhD, director, Inform Division, Center for Forecasting and Outbreak Analytics, CDC.

Michael T. Osterholm, PhD, MPH, director, Center for Infectious Disease Research and Policy (CIDRAP) and professor of public health, University of Minnesota, Minneapolis.

Andrew Pekosz, PhD, professor and vice chair of molecular microbiology and immunology, Johns Hopkins University, Baltimore.

Justin Lessler, PhD, professor of epidemiology, University of North Carolina at Chapel Hill and member, COVID-19 Scenario Modeling Hub Coordination Team.

Amesh Adalja, MD, senior scholar and infectious disease expert, Center for Health Security, Johns Hopkins University, Baltimore.

Jeffrey Shaman, PhD, professor of environmental health sciences and professor of climate, Columbia University, New York City.

CDC: “Weekly US Influenza Surveillance Report: Key Updates for Week 37, ending September 14, 2024,” “Southern Hemisphere Flu Season Could Provide Clues on Upcoming US Flu Season,” “Preliminary Estimated Flu Disease Burden 2023-2024 Flu Season,” “The Changing Threat of COVID-19,” “Staying Up To Date with COVID-19 Vaccines,” “Flu Vaccination Coverage Update.”

FDA: “FDA Approves and Authorizes Updated mRNA COVID-19 Vaccines to Better Protect Against Currently Circulating Variants.”

Rajendram Rajnarayanan, PhD, MSc, associate professor, New York Institute of Technology College of Osteopathic Medicine, Arkansas State University, Jonesboro.