How will the COVID pandemic affect flu season?

Countries in the Northern Hemisphere are facing an unpredictable winter as COVID-19 continues to spread during the flu season, experts have warned.

Last year, when governments recommended a range of protective measures such as mask-wearing, social distancing and lockdowns to slow COVID-19 infections, the number of influenza cases dropped dramatically compared with the seasonal average.

According to the European Centre for Disease Prevention and Control (ECDC) about 20 percent of the population catches the flu each year, but that figure fell by more than 99 percent in 2020-21. There were no hospitalised cases nor fatalities reported from influenza last season.

Cases this year have remained low, according to the World Health Organization (WHO), but with COVID restrictions being lifted in many parts of the world, children back in school, and the coronavirus continuing to spread, experts are urging people to remain cautious. An uptick of influenza cases could burden health systems already facing difficulties due to outbreaks of COVID-19.

What is influenza, and when does the season for it start (North and South)?

Influenza (flu) is a contagious respiratory illness caused by influenza viruses that circulate around the world and are typically more prevalent when it is cold.

According to the United States Centers for Disease Control and Prevention (CDC), there are four types of influenza viruses A, B, C and D.

But “human influenza A and B viruses cause seasonal epidemics of disease known as flu season.”

People with influenza often show symptoms like fever, cough, muscle and joint pain, headache, runny nose and sore throat. Generally, people recover from these symptoms without requiring medical attention, but the virus can also cause severe illness or death, especially in high-risk populations.

According to the WHO, annual influenza epidemics are responsible for about three to five million cases of severe illness, and about 290,000 to 650000 respiratory deaths.

During peak seasons an influenza epidemic can overwhelm health systems. In the Northern Hemisphere, the season can start in October and last until April or May. In the Southern Hemisphere, the season can run from April-September.

Could this season be harder than others?

Experts have said it is difficult to predict the severity of the flu season in the Northern Hemisphere, but some have warned it could be challenging this year.

Last year, influenza activity was dramatically lower compared with the previous years in both the Southern and Northern Hemispheres.

Due to the far lower number of infections last year, the strains circulating this year may be harder for people’s immune systems to detect, which could leave people more susceptible to infection and may even lead to more severe illness.

“Natural immunity wanes, so with little influenza last year, people are more susceptible,” Dr Robert Klugman, medical director of employee health at UMass Memorial Health in Worcester told Al Jazeera.

Dr Amesh Adalja, senior scholar at the Johns Hopkins Center for Health Security, said people continue to take precautions against catching or transmitting COVID-19, which could lead to a milder flu season compared with those before the COVID pandemic.

“A lot of the people are still doing some of the mitigation measures from COVID-19 that had an impact on flu, like social distancing, wearing masks, being careful when they are in a high-risk setting,” said Dr Adalja.

“So I do think that flu is going to be more common this season in the Northern Hemisphere than it was last season, but I think it might be a milder season than the ones we had in the pre-COVID era,” he added.

Experts also warned that an increase in flu cases could overwhelm health systems in countries where COVID-19 hospitalisations are high.

“We have a proportion of people that are still susceptible to COVID-19 infections due to immune problems and not being vaccinated,” Dr Lynora Saxinger, an infectious-disease expert at the University of Alberta, said.

“That could easily overwhelm our health care system and if we just add that layer of influenza on top of that, it would be a high-risk scenario.”

According to Dr Saxinger the influenza season ordinarily “results in health care systems strained”.

Can we get the flu and the COVID-19 vaccines at the same time?

A report released by the Lancet in November said it is safe to administer both vaccines at the same time, noting that giving both shots in one sitting “could reduce the burden on health-care systems”.

“It is quite routine to get multiple vaccines at the same time,” Dr Saxinger said. “I think that is a real opportunity, because people are much more likely to comply or take the second vaccine if it can be done in the same visit.”

Regarding the side effects, Dr Saxinger said some people have almost none and others have some symptoms related to “an immune response.”

The CDC also noted that both vaccines can be “given at the same time”, while adding that side effects are “generally similar whether vaccines are given alone or with other vaccines”.

How can we mitigate risks?

Experts have said that much of the health guidance that has been introduced during the pandemic can help to mitigate the risk of spreading the flu.

According to the CDC, the health measures that help to protect against the flu are: avoid close contact with people who are sick, stay home when sick, wash hands regularly, avoid touching the eyes, nose or mouth, and cover the mouth and nose.

“The measures against COVID worked excellently against influenza,” Dr Saxinger said. “I actually think that if people keep up the use of masks, [and] are judicious about their interactions, it would make a huge difference.”

Dr Ricardo Soto-Rifo of the University of Chile’s Institute of Biomedical Sciences, also highlighted the use of masks.

“The face masks act as a barrier,” Dr Soto-Rifo said. “And it works both ways, they protect you from spreading the virus, but also they keep the virus out,” he added.

“There are different types of masks some better than others in terms of the protection they provide, but they definitely help and make a difference.”

What lessons can the north learn from the Southern Hemisphere?

According to the WHO, the influenza season in the Southern Hemisphere this year was similar to the previous year. In a report released in September, the organisation said that in Australia, the health authorities reported “influenza-like illness activity remained at historically low levels.”

The WHO said that similar trends were also observed in Chile “where sentinel hospital data show influenza activity falling to nearly zero in the spring of 2020 and largely remaining there throughout 2020 and 2021.”

Dr Soto-Rifo said that different variables could explain the low rates of flu.

“In Chile, the vaccination campaign started having an effect, there were also mobility measures well established, and the use of masks was mandatory,” Soto-Rifo said.

“So, we saw how the numbers of deaths and hospital occupation dramatically dropped,” he added.

However, as summer starts in the Southern Hemisphere, and some measures are relaxed, Dr Soto-Rifo said there are concerns that COVID-19 cases concerns could grow.

“Last summer, we saw a dramatic increase of cases, so it’s still very uncertain what follows next,” he added.

According to Dr Soto-Rifo one challenge that Chile did observe during its winter was the rise of rates of respiratory syncytial virus (RSV) in children – this is a common virus that typically infects young people and can sometimes cause pneumonia.

“Children are good vectors of respiratory viruses, but keeping the measures in place helped,” Soto-Rifo said.

“I think the most important thing that we should not forget is that we are still in a pandemic, and as tiring as it might be, we need to keep the health measures in place.”