In what is clearly the worst influenza season since 2009, the flu has hit early and hard. The Arkansas Department of Health (ADH) is currently receiving large numbers of reports of influenza infections, hospitalizations, and intensive care unit admissions from all regions of the state and is already aware of seven deaths from the flu.
Currently in the US, 79.2% of the circulating influenza strains are Influenza A. Of those that are subtyped, 98% bear the H3N2 surface antigens and 2% bear the H1N1 antigens. Nearly all (99.3%) of the H3N2 strains and all of the H1N1 strains tested are well matched with the vaccine. Influenza B accounts for 20.8% of the circulating strains. Of those that are further characterized, 68.7% are well matched with the B component of the vaccine and 31.3% are not well matched. Overall the vaccine is well matched to roughly 90% of all current circulating strains.
No isolates of either Influenza A or B have shown resistance to neuraminidase inhibitor medications.
Only three cases of variant flu (novel influenza viruses from animal origin) have been reported nationally this season. None have occurred in Arkansas.
Amid the reports of illness are reports of people who have fallen ill despite receiving the seasonal flu immunization. In that regard, we have also heard rumors of doctors recommending that patients not get immunized because ‘it doesn’t work.’ These anecdotal reports are particularly concerning.
The ADH wholeheartedly recommends influenza vaccination for all eligible persons six months of age and older. It is very effective in preventing flu infections, hospitalizations, and deaths. Admittedly, it is not perfect and will not protect everyone – but it is the best tool we have. Protection from the vaccine depends on the recipient’s age and immune status and the type of vaccine. Overall, most influenza immunizations provide 60-80% protection against influenza infection. Similarly, they provide roughly 70-90% protection against influenza-related hospitalization.
In Arkansas, we expect approximately 1.5 million people to be vaccinated against the flu this season. If the vaccine keeps 80% of recipients from getting the flu, 1.2 million people would be protected and 300,000 would remain at risk of disease. So it is completely expected to see a minority of vaccinated people develop disease. When a vaccinated person develops the flu, it may be for a number of reasons, including:
1) People may be exposed to an influenza virus shortly before getting vaccinated or during the two-week period that it takes the body to gain protection after getting vaccinated. As a result, the person may become ill with the flu before the vaccine protected them.
2) A person may be exposed to an influenza virus that is not included in the seasonal flu vaccine. There are many different influenza viruses that circulate every year. Characterization of viruses collected this season in the United States indicates that 90% of the circulating viruses match the vaccine viruses; however, 10% of circulating viruses are likely not covered by the vaccine.
3) Unfortunately, some people can get infected with an influenza virus that is included in the vaccine despite getting vaccinated. In general, the flu vaccine works best among young, healthy adults and older children. Some older people and people with certain chronic illnesses may fail to develop effective immunity after vaccination. While vaccination offers the best protection against influenza infection, it’s still possible that some individuals may become ill after being vaccinated.
As background, influenza typically is not a mild upper respiratory infection or cold. Instead, patients graphically describe the onset of the flu as ‘getting hit by a bus.’ This is because the generalized muscle aches associated with the flu can be severe. Classic symptoms also include cough, high fever, headache, and malaise. In children influenza symptoms can include vomiting or diarrhea. The symptoms typically last a week and may last longer.
Persons who develop disease after vaccination often have milder symptoms or a shorter duration of illness and are much less likely to have a serious outcome, such as hospitalization or death from the flu than persons who were not vaccinated. The last thing we as doctors should be doing is to downplay the importance of flu vaccination. Flu immunization remains one of the most important and impactful public health and medical interventions that we have.
Dirk Haselow MD, PhD
State Epidemiologist and Medical Director, Communicable Disease and Immunizations