COVID measures may lead to future outbreaks of other infections

The non-pharmaceutical interventions (NPIs) implemented to reduce transmission of SARS-CoV-2 – social distancing, travel restrictions, mask-wearing, etc – have led to reduced transmission of other circulating infections, such as influenza and respiratory syncytial virus (RSV).
 
‘While this reduction in cases could be interpreted as a positive side effect of COVID-19 prevention, the reality is much more complex.’
 
That is what Dr Rachel Baker believes.
 
She is the first author of a new paper, published in the Proceedings of the National Academy of Sciences on 9 November, that suggests current reductions in certain respiratory infections may postpone the incidence of future outbreaks.
 
‘Our results suggest that susceptibility to these other diseases, such as RSV and flu, could increase while NPIs are in place, resulting in large outbreaks when they begin circulating again,’ Dr Baker said.
 
For the paper, researchers used laboratory surveillance data from 2020 and estimated that RSV transmission dropped by at least 20% in the US at the start of the NPI period.
 
‘We simulate future trajectories of both RSV and influenza, using an epidemic model,’ the authors wrote.
 
They say as susceptibility increases over the NPI period, ‘substantial outbreaks’ of RSV may occur in the future, ‘with peak outbreaks likely occurring in the winter of 2021–22’.
 
Associate Professor Hassan Vally is an epidemiologist with a special interest in infectious diseases at La Trobe University.
 
He told newsGP it makes sense the measures used to control spread of SARS-CoV-2 will result in a flow-on effect on other infectious diseases.
 
‘We’ve changed so much in terms of the way society operates, and we know there’s a complex interaction between diseases, the environment and people – called the epidemiological triad,’ he said.
 
‘We know that all these factors interact with each other.
 
‘Clearly this has been a huge seismic shock to our society and it’s going to have effects on other infectious diseases.
 
‘It’s going to have an effect on chronic disease in the next few years because people are not being screened and people are not exercising and [it will also affect] mental health.
 
‘It’s going to affect everything.’
 
However, Associate Professor Vally says it is not correct to assume that after the pandemic society will abandon all NPIs altogether, leading to a potential surge in infectious diseases.
 
‘This is probably the biggest social and behavioural change in society that has occurred maybe since the Depression or the world wars,’ he said.
 
Even in the influenza pandemic of 1918, Associate Professor Vally says, the change in people’s behaviour occurred in ‘shorter bursts’.
 
‘But this has occurred for such a long time,’ he said. ‘The point is that the big unknown in this modelling is how people’s behaviour changes in a more permanent way as a result of living through this pandemic.
 
‘So there’s quite a bit of uncertainty in terms of their modelling and extrapolating beyond where we are now.
 
‘The big unknown is, will people just bounce back to their pre-pandemic behaviour?
 
‘We’ve experienced such a duration of changing our behaviour, we may never bounce back to exactly where we were.’


Associate Professor Hassan Vally says it is important to consider potential future health issues that may stem from measures used to control the current pandemic.

While the researchers found NPIs could lead to a future increase in respiratory infections, the effect was greater for RSV than for influenza.
 
According to Dr Baker, vaccines could make a ‘big difference’ in future cases of influenza.
 
‘In addition, the impact of NPIs on influenza evolution is unclear but potentially very important,’ she said.
 
Associate Professor Vally agrees with the notion it is more difficult to predict the impact of NPIs on future influenza outbreaks, compared to RSV.
 
‘There’s even more uncertainty around influenza because the influenza virus is more mutable and it can change a lot more,’ he said.
 
‘So there are a lot of unknowns.’
 
The authors found that even relatively short periods of NPIs could lead to large future RSV outbreaks, but that longer periods are likely, in general, to lead to larger future outbreaks.
 
However, they say these may display ‘complex interactions with baseline seasonality’.
 
This makes sense to Associate Professor Vally.
 
‘What they’re really saying is by not being exposed to these infections for such a long period, people will have less immunity,’ he said.
 
This is not the first time such issues have come to light.
 
The researchers note that ‘evidence from the 1918 influenza pandemic suggests that NPIs may have reduced measles transmission by 38%’.
 
Meanwhile, control measures used to reduce spread of SARS-CoV-2 in Australia have also had an effect on other viral infections.
 
In June, newsGP reported that Australia’s flu numbers had plummeted after social distancing measures were put in place in mid-March, with laboratory-confirmed cases in April and May 2020 down by nearly 93% compared to the same period in 2010–19.
 
At that time, Professor Ian Barr, Deputy Director of the World Health Organization (WHO) Collaborating Centre for Reference and Research on Influenza at the Doherty Institute, told newsGP that while the flu is unpredictable, low numbers of infection might have follow-on implications.
 
‘[C]ertainly you would expect, logically, that if we have fewer people infected this year that we’ll have less herd immunity going forward, unless the vaccine can pick up some of that slack,’ he said.
 
Associate Professor Vally says the new paper offers important information to consider for the future.
 
‘It’s interesting to think about the more medium- to long-term effect on other diseases, because everyone’s talked about the immediate reduction in disease levels, but thinking ahead to what may happen down the track is really interesting,’ he said.
 
Dr Baker agrees.
 
‘It is very important to prepare for this possible future outbreak risk and to pay attention to the full gamut of infections impacted by COVID-19 NPIs,’ she said.
 
However, with so many uncertainties, Associate Professor would not be willing to predict what will happen from here in terms of the effect of NPIs on other diseases.
 
‘But this is definitely one possibility and there’s good logic behind this thinking,’ he said.
 
‘There’s no doubt that what we’ve been through will affect both chronic and infectious diseases in the next few years, so it’s good to be aware that there are challenges ahead.
 
‘I think it’s really important to be thinking about these things so that we are prepared.
 
‘Forewarned is forearmed.’
 
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influenza non-pharmaceutical interventions social distancing