Influenza, also known as the flu, is one of the most common viral diseases in the world. It, however, took a backseat when the new coronavirus, SARS-CoV-2, rapidly took over earlier this year.
Now, new research, published in BMJ, shows that governments’ implementation of lockdowns and physical distancing measures, in an effort to curb the spread of SARS-CoV-2, have shortened the flu season – by up to six weeks, and that tracking infectious disease cases “could be a complementary approach to assessing the effectiveness of general infection control measures against Covid-19”.
Flu viruses circulate worldwide at different times of the year. Seasonal flu usually peaks in February and dies down by the end of May in the northern hemisphere, and runs from April to September in the southern hemisphere, often peaking during August.
Death by flu: a global perspective
Statistics from the World Health Organization (WHO) indicate that the seasonal flu typically kills around 290 000 to 650 000 people annually and causes as many as five million cases of severe illness. According to Nature, the 2020 flu season was set to be the most severe in decades, until Covid-19 crossed borders and was declared a pandemic.
In South Africa, flu kills between 6 000 and 11 000 people each year, according to the Department of Health. So, if flu seasons are shortened around the world, it could mean that more lives are spared.
Lab-confirmed cases from this year so far reveal that the incidence of flu dropped steeply in early April in the northern half of the world. This was revealed just a few weeks before the new coronavirus was declared a pandemic on 11 March. The data came from FluNet, a global surveillance system, and included tests of more than 150 000 samples from national influenza laboratories in 71 countries.
Business Insider reported in March that at least 20% of the global population was on lockdown, with South Africa, India, China, France, and Italy, among others, having the world's most restrictive quarantines. By the end of March, more than 100 countries worldwide had instituted either a full or partial lockdown, the BBC notes.
On the other hand, an article in Nature points out that, looking at the total number of lives lost to Covid-19 and other diseases in 2020, it’s hardly a rosy picture that emerges.
The case with other infectious diseases
A number of other infectious diseases such as chickenpox, measles and rubella were also positively impacted so far in Hong Kong this year, the study’s co-author, infectious-disease researcher Pak-leung Ho at the University of Hong Kong, told Nature, with measles and rubella being at their lowest, globally, since 2016. Ho explained that the closure of schools during lockdown could have been the reason behind this, as these diseases typically affect children, adding that this “may have had the biggest impact”.
By contrast, there are other infectious diseases, such as tuberculosis (TB), that are likely to see an upsurge in cases, as programmes to fight the disease have been cast aside since the Covid-19 outbreak. TB is ranked as the ninth leading cause of death worldwide.
A recent release of modelling on the impacts of the initial Covid-19 response on TB revealed an estimation that, globally, a three-month lockdown and a protracted 10-month restoration could lead to an additional 6.3 million people falling ill with TB and an additional 1.4 million TB deaths over the next five years, Health24 reported. According to the latest statistics by WHO, TB caused around 63 000 deaths in South Africa in 2018 (figures for 2019 are not yet available).
Tracking ILI cases
Of course, the reported decline in flu cases may also be due to people with flu-like symptoms simply avoiding health clinics during this time, and self-isolating at home instead. But tracking the number of flu cases and other influenza-like illnesses (ILI), can, however, help shed light on the effectiveness of public health policies aimed at containing the Covid-19 pandemic, the authors of the paper note. This recommendation comes after the team looked at the epidemic response in Hong Kong, whose 2019–2020 flu season was 63% shorter than those of the previous five years. Lab-confirmed flu deaths showed that the number was 62% lower.
In their paper, they explain, based on the statistics, the key infection control strategies undertaken in the country against Covid-19 – case identification and isolation, quarantine, physical distancing, and mass wearing of masks – provide evidence that surveillance of these diseases can provide crucial information about the impact of general infection control measures.
“By monitoring the transmission patterns of ILI, we can approximate the overall performance of a population’s general infection control measures, including enhancement of personal and environmental hygiene and physical distancing,” the authors wrote.
WHO also told Nature: “Public-health measures such as movement restrictions, social distancing and increased personal hygiene likely had an effect on decreasing influenza and other respiratory virus transmission.”
Covid-19, which started as a local outbreak in China and quickly led to a pandemic, has infected over 5.4 million and caused more than 346 000 deaths worldwide – as of 26 May 2020.