Cheryl Cohen, associate professor in epidemiology at Witwatersrand University in South Africa, said: "The spectre of colliding epidemics is a concern. Should the two epidemics be overlaid, that would obviously be really worrying."
The World Health Organization has warned of the difficulties faced by some countries in obtaining flu vaccines as supplies are snapped up. "Whoever has extra flu vaccine let us know," Ann Moen, the group's head of influenza preparedness and response, said at a conference last month.
The 1.5m doses that Turkey expects to receive this year will be insufficient, according to the country's pharmacists association. "With Covid-19 we think there's a need for three to four times that," said Erdogan Colak, the group's president. This claim is refuted by Turkey's government.
Concerns about the two respiratory illnesses compounding one another — and the impact on health systems — has led governments to act fast to begin strict flu inoculation programmes in place of what were previously voluntary and unenforced campaigns.
John McCauley, director of the worldwide influenza centre at the Crick Institute in London, said it "would be remiss" if governments did not increase flu vaccinations this year. Flu vaccine had prevented 15-52 per cent of UK cases over the past five years, according to Oxford university research. The wide range is because in some years the vaccine is less well matched to the circulating strains, which constantly mutate.
Up to 650,000 people die from influenza each year globally, according to the WHO, compared with more than 1m from Covid-19 so far this year.
Last year, before coronavirus boosted demand for flu vaccines, Seqirus estimated that 650m vaccine doses would be bought by governments and health bodies in 2020, costing $5bn.
After the Australian government called on more of its population to get the flu jab, imports of vaccinations jumped to a record high of 18m doses, up from an average of 8m doses from 2012-2017.
But as demand surges, supply has only increased marginally. "Manufacturers can extend their campaign up to a point, but at that short notice there's a limit to what we can do," said Beverly Taylor, head of influenza scientific affairs at Seqirus. Companies would normally need 12-18 months' notice for any large-scale manufacturing scale-up.
"Some governments have offered things before there was sufficient supply. They should have checked first," she added.
GSK said it was "looking at all opportunities to produce and distribute more flu vaccine doses for 2020 and the coming years, but expects demand to continue to outpace manufacturing capacity". It said it was "very difficult to quickly adjust manufacturing capacity to match changes in demand".
Experts also noted that levels of influenza have been exceptionally low so far this year in the southern hemisphere — which normally experiences a peak from June to August. The same trend had been observed in other serious respiratory diseases, such as pneumococcal, rotavirus and respiratory syncytial virus.
Prof Cohen attributed this "unprecedented reduction" in flu cases to measures adopted to contain coronavirus, including the use of masks, handwashing and limits on mass gatherings. And for illnesses such as flu and RSV, for which children are responsible for most of the spreading, school closures are thought to have played a significant role.
"It does make you wonder whether masks and social distancing could help in the future," noted Mr McCauley.
Video: Coronavirus: the global race for a vaccine | FT InterviewThe relative absence of flu has thrown up a few challenges, however. For one, scientists such as Mr McCauley spend months each year analysing new influenza strains to tailor vaccine production for the following year. Without much influenza in circulation, it is difficult to know if new mutations will be picked up, meaning vaccines from 2021 could be less effective.
And some see the lack of flu so far this year as an ominous sign of what might be to come. "Could a lack of immunity this year increase the scale of the epidemic next?" Prof Cohen asked.
Flu experts agreed that the priority was to increase production and ensure that the public actually takes the vaccines already procured. In Germany for example, up to 8m unused flu vaccine doses are destroyed each year.
- Financial Times
