Winter is coming to the north. If聽what happened in the southern hemisphere is any guide, anti-coronavirus measures could result in fewer people than usual getting flus and colds. The respite may be brief, though. These viruses could come roaring back when measures to limit the spread of covid-19 end.
If fewer people susceptible to these viruses are infected this year, there will be more susceptible people around next year, says Daniel Yeoh at Perth Children鈥檚 Hospital in Australia.
If we fall ill at the moment, we聽tend to worry that we have covid-19, especially if we have a fever or a cough. But such illness is more likely to be due to cold or flu viruses than to the coronavirus.
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鈥淐olds and flus still dominate over the coronavirus overall,鈥� says聽Claire Steves at King鈥檚 College London, a member of the team behind the COVID Symptom Study app. The app鈥檚 users in the UK, US and Sweden report daily whether they are well or have symptoms.
Between 8 and 21 August, for instance, just 0.4 per cent of UK app users who reported symptoms of illness tested positive for the coronavirus, says Steves. People reporting a runny nose and swollen glands were unlikely to test positive, but 90 per cent of those who did have a positive test had severe headaches and fatigue.
Another study of key workers in聽the UK found that only half of聽the people who thought their symptoms indicated covid-19 actually had the disease.
Measures being taken to try to stop the spread of the coronavirus are also making it harder for other respiratory viruses to spread. 鈥淭he聽social distancing works for other viruses as well,鈥� says Steves.
In some places, the effect has been dramatic. Normally the number of people who go to hospital with an illness diagnosed as flu or respiratory syncytial virus聽climbs sharply every winter. This winter, in Western Australia, the number of reported cases instead fell to zero most weeks, Yeoh鈥檚 team has reported.
In fact, Australia, Chile and South Africa have reported just 51聽positive results for flu out of 80,000 tests done during the southern hemisphere winter. In the previous three winters, these countries reported 25,000 positive results out of about 180,000 tests.
Fewer flu cases than normal were also reported in the northern hemisphere summer. 鈥淭he numbers are low,鈥� says John McCauley at the World Health Organization. He says that many resources usually dedicated to monitoring flu are now monitoring coronavirus instead. 鈥淲e could be underestimating prevalence,鈥� he says.
It is less clear what is happening with other respiratory viruses such as rhinovirus, adenovirus and parainfluenza virus as they seldom cause serious illnesses so there is no systemic surveillance in most countries. However, the US Centers for Disease Control and Prevention (CDC) monitors them.
鈥淧ositive detections of non-influenza respiratory viruses have been lower than we would expect in August and September with the exception of rhinovirus/enterovirus,鈥� says a CDC spokesperson.
What matters is what happens during the northern hemisphere鈥檚 winter, when the number of cold and flu infections usually peaks. Flu cases add to the pressure on healthcare systems, which is why it is more important than normal that people get the flu vaccine this year. Fewer flu cases than usual may occur where anti-coronavirus measures are in place, but not as聽few as in Australia.
鈥淭here are a聽couple of key differences in Australia that may have combined to lead to the very low numbers seen here,鈥� says Yeoh.
Australia imposed its lockdown just before winter in the southern hemisphere, whereas most northern hemisphere countries don鈥檛 have lockdowns in place now. Australia also instituted strict聽travel restrictions that remain in place, limiting the odds of flu being reintroduced from other countries, says Yeoh.
Indeed, in the UK, the number聽of people reporting symptoms of illness between 8聽and 21 September is up by 74 per cent compared with the same period in August, says Steves. The聽percentage testing positive for covid-19 is up too, at 2.8 per cent.
She says that viruses other than the coronavirus were probably largely responsible for this surge after schools reopened, but within聽this聽there was a concerning rise in聽covid-19 cases too. As coronavirus restrictions lift, and with potentially more susceptible people next year, we could see a spike in future colds and flus.
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