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Flu warning: Infections likely to soar in 2018

Compounding the longer duration and severity of the outbreak is the worrying news that the vaccine effectiveness against H3N2, which is the predominant influenza strain this winter, is only 10%

columns Updated: Dec 10, 2017 09:48 IST
Sanchita Sharma
Sanchita Sharma
Hindustan Times
Flu,seasonal flu,influenza
Seasonal flu causes symptoms of fever, cough, breathlessness, lethargy, headache and nausea.(Shutterstock)

Seasonal flu will hit India and the rest of the northern hemisphere hard next year, predict flu-trackers based on outbreak trends in the winter of the southern hemisphere, where Australia has reported record-high numbers of cases, hospitalizations and deaths.

Australia had 233,453 lab-confirmed cases of seasonal flu till mid-November, compared to 87,333 during the same period last year, with hospital admissions up 2.3 times the five year average.

Compounding the longer duration and severity of the outbreak is the worrying news that the vaccine effectiveness against H3N2, which is the predominant influenza strain this winter, is only 10%.

Since several different viruses cause seasonal influenza and these viruses are subject to continual antigenic changes (“antigenic drift”), World Health Organization (WHO) every year recommends a new strain-specific vaccine in February for the northern hemisphere and in September for the south to prevent infection. Each new vaccine targets three to four of the most deadly flu strains causing infection based on flu-tracking data from the previous five to eight months from 143 National Influenza Centres in 113 countries, including India.

Seasonal flu infection peaks between June and October in India, Bangladesh, Cambodia, Philippines, Thailand and Vietnam, with India, Thailand and Vietnam registering an additional minor peak from December to February, shows WHO research. (Mohit Suneja)

If the viruses causing infection change, so does the recommended strain-specific vaccine. And since there are always several closely related strains circulating, experts combine antigenic and genetic characterization and modelling to predict which strains will cause the most disease in the coming months.

Shot In Time

Seasonal flu causes symptoms of fever, cough, breathlessness, lethargy, headache and nausea. Most people recover within a week without ill-effects, but complications such as pneumonia and multi-organ failure can kill people at risk, such as young children with respiratory problems, pregnant women, older adults above age 65 years, and those with chronic disorders such as asthma, lung diseases, heart disease and diabetes.

Seasonal flu infection peaks between June and October in India, Bangladesh, Cambodia, Philippines, Thailand and Vietnam, with India, Thailand and Vietnam registering an additional minor peak from December to February, shows WHO research. Infection in equatorial Indonesia, Malaysia and Singapore occurs throughout the year.

For 2017-18, the WHO recommended the trivalent vaccine that protects against A/Michigan H1N1, A/Hong Kong H3N2, and B/Brisbane viruses. The quadrivalent vaccine also includes B/Phuket virus.

Seasonal influenza outbreaks each year cause 3 million to 5 million severe cases and 300,000 to 500,000 deaths globally, estimates the WHO. Since the recommended vaccine for the coming flu season in the northern hemisphere, including India, is the same as the one that was mostly ineffective against H3N2 in Australia, epidemiologists predict a potentially severe influenza season in the north, with more severe disease, hospitalizations and deaths.

This is indeed worrying because even in years when influenza vaccines are well matched to circulating viruses, vaccine effectiveness ranges between 40 per cent and 60 per cent, which is lower than protection offered by vaccines against other diseases, reports a paper in the New England Journal of Medicine.

If there is a mismatch between the vaccine and the circulating influenza strains, effectiveness falls further. In 2014–15, when more than 80 per cent of the circulating H3N2 viruses characterized differed from the vaccine virus, vaccine effectiveness was 13 per cent.

Lab Boost

Apart from vaccine design, the other major factors that determine its effectiveness are whether the recipient has had previous exposure to influenza, vaccination history, age and coexisting conditions, which almost always lower immune response in sick and older persons who need the highest immune boost.

To improve protection, scientists have begun identifying novel vaccine antigens, platforms and manufacturing strategies to improve vaccine design. Trials for a new “universal” vaccine that stimulates the immune system to boost the body’s own immunity-building influenza-specific T-cells begin in Berkshire and Oxfordshire in the UK this winter. Previous research shows that T-cells, which all of us have but in numbers too insufficient to destroy infection, can help fight more than one type of flu virus over a few years. If successful, it will not just offer universal protection but also do away the need for annual vaccinations.

With its efficacy under scanner, should you get vaccinated against the flu at all? However imperfect the vaccine may be, say NEJM researchers , it is always better to get vaccinated than not to get vaccinated.

In India, since 70 per cent cases are reported between June and November, the best time to get flu shots is between April and June, recommends the WHO.

With H1N1 already being particularly virulent in 2017 – till November 26, India confirmed 38,220 cases and 2,186 deaths from H1N1, one of the three viruses causing seasonal flu, compared to 1,786 cases and 265 deaths in 2016 – people at risk must consider getting vaccinated to prevent infection and lower severity of disease.

First Published: Dec 09, 2017 23:03 IST