Doctors on whether adults should take the flu vaccine and its efficacy against Covid-19

What is the flu shot all about?

The Center for Disease Control (CDC) says that the flu vaccine protects against influenza and a lot of other diseases. Amid Covid pandemic, an additional flu illness will only add to the problem. “Hence, as per the CDC, while the flu vaccine itself doesn’t protect against Covid-19 directly, but it protects against other kinds of flu, and in turn, can prevent the burden of the disease. Also, there could be an instance where somebody has got influenza and Covid both which may increase the morbidity or mortality in that case,” said Dr Manish Mannan, HOD- paediatrics and neonatology, Paras Hospitals Gurugram.

A March 2021 study conducted in the Michigan medical healthcare system in the US noted that in a retrospective study from February-July 2020, it was found out people who were given the flu shot were less susceptible to testing positive and those who had tested positive had lesser chances of getting a severe illness, which reduced hospitalisation concerns.

“So, while more data is required on whether or not flu vaccine will protect directly against Covid, but we can definitely say that since normal influenza, flu and Covid symptoms are quite similar, people will be at least protected against one illness,” he mentioned.

How does flu vaccine help build immunity?

The Michigan study data suggests that flu vaccine may have some role in protecting against Covid, but there is also an entity known as the ‘off-target effect’ of a vaccine in which the vaccine, apart from its target, also has some non-specific immunomodulatory effect beyond protection against the target disease, explained Dr Mannan.

Patients who had received influenza or flu vaccine were found to have 24 per cent lower odds of testing positive for Covid-19, according to another recent study published in the American Journal of Infection Control in February 2021. “But, there were no significant differences observed for mortality or use of intensive care units. As per the investigators, ‘Until the COVID-19 vaccine becomes widely available, the influenza vaccine should be promoted to reduce the burden of disease during this pandemic,” highlighted Dr Sudip Chowdhury, consultant paediatrician, Columbia Asia Hospital, Palam Vihar, Gurugram.

The off-target effect of a vaccine is when a non-specific immunomodulatory effect is observed beyond protection against the target disease.(Source: Express Photo by Amit Chakravarthy)

Is taking flu vaccine a good enough measure against Covid, too?

The flu is caused by H1N1 virus and Covid is caused by coronavirus. “Covid and flu diseases have Coryza cough respiratory symptoms but it is difficult to predict that the vaccines against Influenza virus will be protective against Covid. Both are different and need different defense mechanisms. The vaccine shots gear up the immunity, but it is unlikely to save one from Covid even if it presents similar symptoms,” said Dr Arvind Aggarwal, senior consultant, internal medicine, Sri Balaji Action Medical Institute.

So, who can take the flu shot?

According to Dr Rajkumar, senior consultant, Indian Spinal Injuries Centre, as per CDC in the US, flu shots are advisable for “everyone aged 6 months or more. But the protection it provides varies from one season to the other”.

“It also depends on the age and health status of the recipient and the similarity between the viruses in the vaccine and those circulating that season. Even when the flu match between the flu vaccine and the circulating virus is good, the benefits may vary, depending on factors like the health and age of the recipient. Last year, when the pandemic was affecting people, many doctors administered flu vaccines to patients to avoid re-infection. We need a comprehensive study as to how far and well they worked. Flu vaccines may reduce the chance of developing flu-like symptoms in people infected with Covid-19, but there are other symptoms and complications which flu vaccine may not help with. This is the reason why people must get Covid vaccines,” said Dr Rajkumar.

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