What does COVID-19 mean for this year’s flu season?
Every winter, hundreds of thousands become infected with seasonal influenza, which kills between 290,000 and 650,000 people worldwide each year. But this year, we have another respiratory illness to contend with: COVID-19. So, what does this mean for this year’s flu season?
- 29 September 2020
- 5 min read
- by Priya Joi
The flu virus spreads when people breathe in respiratory particles from the sneezes and coughs of someone who is infected, or when they touch surfaces which are contaminated with the virus. The best advice to avoid the flu is to not be in crowded areas with poor ventilation, not go to work places or schools where others are infected, and to wash your hands regularly. This year, the southern hemisphere’s flu season coincided with the start of the COVID-19 pandemic, which had a dramatic impact on cases of influenza. The measures introduced to prevent the spread of COVID-19, with human contact reduced to almost zero, increasing wearing of surgical and cloth masks and the increase in regular hand washing, meant there were virtually no flu cases.
Lockdown wiped out the flu season in the South
Seasonal flu kills about 0.1% of people it infects, but since it spreads easily, it is estimated to kill on average 389,000 a year (about 2% of all annual respiratory deaths). Of these deaths, 67% were among people aged 65 years or older.
South Africa sees around 11,000 flu deaths every year. To keep track of cases, its National Institute for Communicable Diseases (NICD) undertakes rigorous flu surveillance, involving random laboratory screening. Usually, this would identify about 1,000 cases of flu, but by the end of March, the institute recorded only a single case.
A similar pattern has been observed elsewhere. For instance, a study of flu activity during COVID-19 showed that between April and July 2020, only 33 cases were found among 60,031 specimens tested in Australia, 12 in 21,178 specimens in Chile, and six in 2,098 in South Africa – a total of 51 influenza positive specimens out of 83,307 tested (0.06%). By contrast, during the same months in 2017–2019, 24,512 specimens tested positive for influenza among 178,690 across these three countries. That’s 13.7% - so significantly higher than this year.
The best advice to avoid the flu is to not be in crowded areas with poor ventilation, not go to work places or schools where others are infected, and to wash your hands regularly.
How bad will the northern hemisphere’s flu season be?
The COVID-19 lockdown also had a positive effect on the northern hemisphere’s flu season, which was tailing off at the start of the pandemic. In the United States, there was a 98% decrease in flu sample specimens testing positive, from 19.34% in September to February, down to just 0.33% between March and May.
In many countries with unusually low numbers of flu cases, reduced testing may initially have contributed, But when public health officials and clinicians made renewed efforts to identify adequate numbers of samples to test, they still found little trace of the influenza virus.
So, what does this mean for the northern hemisphere over the coming months?
The main difference now, say scientists, is that whereas countries were shutting down at the start of the southern flu season, they are now opening up – including re-opening schools, which is a major contributor to the spread of flu. It’s true that life has not totally gone back to the ease of movement of pre-pandemic days. In Spain, for example, measures taken to reduce the spread of COVID-19 in schools, such as smaller class sizes, frequent hand-washing and requiring children over the age of six years to wear masks all day, could also slow the spread of flu.
But countries are implementing more varied and complex restrictions around COVID-19 than they did back at the start of the pandemic, meaning many people have far more social contact now than they did during lockdown. Even with continued guidance to maintain social distancing, wear masks and wash hands, pandemic fatigue could mean that people are tiring of these measures, or taking them less seriously than when COVID-19 first emerged.
Why the flu vaccine is more important than ever
The prospect of the northern hemisphere flu season swamping countries with influenza cases as well as COVID-19 is grim; co-infection with both respiratory viruses could be deadly. Many countries are already seeing a second wave of the coronavirus cases and the additional burden of caring for people with flu could be disastrous. Plus, people with flu symptoms will need testing to rule out COVID-19, and testing systems are already under strain almost everywhere.
Also, there could be an unexpected downside to fewer cases of flu: every year, researchers study circulating influenza viruses to guide the composition of the flu vaccine for the following year. Less circulating flu virus means it is harder to know which genetic variants have been most common, and are therefore most likely to be the dominating ones the following year. By the end of this month, flu experts will need to settle on the make-up of next year’s flu vaccine for the southern hemisphere.
During these uncertain times, flu vaccinations will be more important than ever - especially for older people or those with underlying conditions. Because of this, flu vaccine manufacturers such GlaxoSmithKline and AstraZeneca are ramping up production for the 2020-21 season in northern countries. The US CDC is expected to produce up to 198 million doses - an increase of 20 million compared to last year. Similarly the UK is expanding the age groups eligible for a free flu shot among both children and adults.
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