As H3N2 flu cases spiral, which vaccine should you take? Why your geographical location matters

What are distinguishing characteristics of the flu this year?

While common symptoms are headaches, sore throat, cough, fatigue, malaise, fever, congestion, loss of appetite, vomitting and diarrhoea, the H3N2 can trigger complications even in healthy individuals. These could be pneumonia, acute respiratory distress syndrome (ARDS), sepsis (a whole-body reaction to an infection) inflammation in the brain and heart muscle.

What’s the right time to take a flu shot?

It depends on whether you are in the northern or southern hemisphere. Dominating circulating strains can change between hemispheres and every year each hemisphere gets a flu vaccine recommendation to last that year.

Every February, the World Health Organisation (WHO) declares four strains which are prevalent in the northern hemisphere for a year. This means that we must go by its projection for the 2025-2026 period. This vaccine is released every May. Similarly, the WHO identifies four strains for the southern hemisphere in April. This would be the most recently available vaccine. The WHO recommends this vaccine for India because the flu season, just after the rains and lasting till November, here is more aligned with the southern hemisphere’s winter.

But if the southern hemisphere vaccine is not readily available, take the latest available quadrivalent (protecting against four strains) influenza vaccine.

Which vaccine is the most recommended?

The tetravalent vaccine, which protects you from four strains —- H151, H3N2 and two influenza B strains. These cost anything between Rs 2,000 to Rs 2,500 annually.

Who should not take the vaccine?

Those who are allergic to eggs should be cautious. The influenza virus used in vaccines is often grown in fertilized chicken eggs — the virus is injected into the egg, allowing it to replicate, and then harvested for vaccine production. Flu viruses have a natural affinity for avian hosts, making eggs a suitable medium for their growth.

Those allergic to eggs should do so only in a hospital setting if the gains far outweigh the risk of an allergic reaction. Studies have shown that severe reactions are extremely rare but lest one happens, a clinical facility helps. Of course, these days there are egg-free vaccines too which use a cell-based method, certain proteins, to grow the virus without the need for eggs.

What is the efficacy of a vaccine?

In healthy children and adults, the efficacy is around 40 to 60 per cent. That drops in an ageing patient. However, do not get confused by efficacy and overlook that it can prevent severe illness, reduce chances of developing pneumonia, hospitalisation and protect vulnerable people through reduced transmission risks.

What about vaccine coverage?

That’s very low in our country. Among healthcare workers, there is 30 per cent coverage. Among older adults with co-morbidities, coverage is only 1.5 per cent. There is very thin data on children, pregnant women and the elderly. In other words, coverage is still poor.

Also, flu shots are not part of the national immunisation programme and are mostly administered at private hospitals. That’s a deterrent for mass use.