How is Covid-19 different from monsoon flu? A doctor explains

Indian Express

28-05-2025

Even as cases of Covid-19 rise across the country, the early monsoon has meant that influenza cases are also spiralling. How then does one differentiate between the two viruses as they have almost overlapping symptoms like fever, sore throat, cough, fatigue, headaches, body aches and diarrhoea?
'Clinically, it is difficult to tell the difference between the two from symptoms alone. Testing is needed to confirm a diagnosis. These are respiratory viruses that can spread from person to person. But yes, given the mutations that we are seeing in sub-variants of Covid-19, we can say these are more transmissible as these trick your immune system faster. But their effects continue to be mild in line with what we have seen in the Omicron variant. The only difference on the surface could be in the severity of symptoms,' says Dr Suranjit Chatterjee, internal medicine specialist, Indraprastha Apollo Hospitals, New Delhi.
However, for the immuno-compromised, the elderly and those with co-morbidities, testing is recommended to avoid complications.
The biggest difference is the dipping oxygen saturation. The oxygen levels fall much more rapidly in Covid-19 compared to flu. Of course, we have seen pneumonia and low levels of oxygen in flu too, especially when the patient has co-morbidities. But the dip among all age groups is sharper in Covid-19.
Loss of smell or taste used to be a distinguishing factor but with newer variants, these symptoms do not show up. Besides, you could lose your sense of smell and taste even in bad cases of flu.
Covid-19 can cause more severe symptoms in some people compared to the flu. Not only that, a flu may result in symptoms between one and four days after infection. In Covid-19, a person may experience symptoms anywhere from two to five days and up to 14 days after infection, according to the Centres for Disease and Control (CDC). Also, in flu cases, the disease tends to ease out and resolve faster than Covid-19, whose symptoms tend to intensify and even become long-lasting. The latter may even lead to multi-system inflammation that may last a longer time.
If a person has Covid-19, they could be contagious for a longer time than if they have flu. People with influenza virus are potentially contagious for about one day before they show symptoms. But Covid-19 patients can spread the virus days before their symptoms begin and can be contagious for a week after their symptoms begin. In other words they are more superspreading.
Testing is crucial for accurate diagnosis and treatment. While flu is generally diagnosed going by symptoms, if you are in an area where Covid-19 is rampant, then go for the RT-PCR. Early testing can help reduce severe illness.
Do not miss out on the flu vaccine shot, which is updated every year. Covid vaccines were based on ancestral strains and cannot protect us from sub-variants. Vaccines that do so are not widely available. We have protection from earlier vaccine shots and have infection-acquired immunity. With mild symptoms, no vaccine guideline has been issued.