Firstly, let’s look at the bigger picture, co-infections of diseases happen all the time. Bacterial co-infections in hospitalised COVID-19 patients have occurred in around 7% of cases, with viral infections lower, at 3%. In the early phase of the pandemic, scientists in Wuhan reported in one study that just over half of the 307 cases of COVID-19 they diagnosed had evidence of influenza infection, although this could have been due to a localised outbreak. To date, co-infection of influenza and SARS-CoV-2 has however not been commonly reported. A more recent analysis of research on the subject suggested 1.2% of COVID-19 patients reported influenza co-infection. The data on co-infection incidence is not however particularly clear, noting that influenza testing is not currently widespread globally.
The impact of seasonality
These figures were however pre-omicron. Scientists have also been wondering how, in South Africa, many cases of omicron were largely free of symptoms, yet in the northern hemisphere symptomatic infection has been more common. South Africa saw its omicron wave occur in the summer months: whilst in one widely reported study in Norway, where 74% of attendees were infected with omicron at a Christmas party, almost all were symptomatic. Whilst a higher viral load found in more closed indoor environments with poor ventilation is a factor in promoting greater chances of symptomatic disease, are the two viruses simply co-habiting with each other more readily in the winter season and thus causing more symptoms? Recent studies have also pointed to an intriguing possibility of viral interference, where one virus somehow blocks replication of the other. More studies will be needed to work out how exactly these two viruses interact.
The role of the employer
We do that having both COVID-19 and influenza together can be problematic; for those with pre-existing conditions, the complications can be particularly severe. Simultaneous infection with influenza and SARS-CoV2 can thus interfere with the diagnosis and treatment of patients. In addition, COVID-19 often presents with very similar symptoms to the common cold or influenza leading to time off work for testing or isolation.
Many employers have renewed efforts to drive flu vaccination programmes in their workforces; in addition to the continued role employers are playing in supporting rollouts of COVID-19 vaccination this can a valuable tool in the fight to preserve our hospital capacity and protect the most vulnerable in our communities.
The epidemiological picture is changing rapidly however. It is critical for businesses to be able to plan ongoing health responses, answer employee questions and concerns credibly, and help address medical misinformation head-on. Our medical advisors in the International SOS consulting practice are on-hand to help clients answer such questions.