With its unique tendency to undergo frequent mutation, influenza is a moving target with boundless capacity to surprise and confound. This flu season appears to pack a double punch: it’s unusually virulent, and the vaccine is not optimally effective.
This year’s prevailing strain is A(H3N2); the H1N1 pandemic of 2009 notwithstanding, H3N2 is generally associated with more symptomatic cases, more hospitalizations and more deaths.
There are several possible explanations for low vaccine efficacy. Bear in mind that selection of the vaccine strains must be made nearly a year in advance of flu season to allow for the manufacturing process – plenty of time for circulating viruses to change disguise several times (especially H3N2, which mutates at a faster pace than the others). Additionally, the virus selected for the vaccine may undergo changes that reduce its antigenicity during the egg-based manufacturing process. Efficacy of this year’s vaccine is estimated to be about 20 percent to 30 percent overall, though there are likely variations in the efficacy for each component virus.
So, how can we prevent influenza?
Even with a suboptimal vaccine, there are still arguments to be made in favor of vaccination, and misperceptions about it that should be addressed:
- “The flu shot gave me the flu one year, so I don’t get one anymore.” While acknowledging the limitations of the vaccine, we should recognize that it is very safe and does not cause some of the effects attributed to it. This year, all available vaccine in the US is made from killed virus or viral antigens, and can’t cause influenza. The likely reason for this commonly held claim is that the person experienced the low-grade fever and mild achiness that sometimes occur with the vaccine (but do not represent infection), or developed a respiratory infection due to a different virus.
- “It’s never worked for me – I get sick anyway.” Many people have unrealistic expectations of the vaccine, stemming from misunderstanding about what influenza is (and isn’t). The term “flu” has been generalized to mean almost any winter illness. The result of this common (but inaccurate) usage is that many people believe the vaccine should protect them from all kinds of common colds, gastrointestinal viruses and the like, and they are disappointed when it fails to provide all-inclusive protection. The truth is that true influenza is a severe respiratory infection that causes as many as 50,000 deaths in the US every year. This is the disease the vaccine is designed to prevent. While young children, older adults, and people with certain chronic conditions are more vulnerable to severe illness and complications, this year’s strain may be more indiscriminate, as reports of deaths in young, healthy adults are surfacing.
- “This year’s vaccine doesn’t work for the current flu.” The prevalence of A(H1N1) and B strains is continuing to increase as this season unfolds. Historically, vaccine efficacy against these strains has been greater than against A(H3N2). Also, even with suboptimal immunogenicity, the vaccine may mitigate symptoms. In view of the severity of disease seen during this season, a reduction in morbidity could be of great benefit. Influenza is highly contagious; so even for those at low risk for severe disease, prevention or mitigation of infection may save a life by avoiding spread to someone more vulnerable.
- It’s too late to immunize for this season. Actually, it’s not too late. We can expect influenza to be with us well into April. The vaccine is recommended for all persons aged 6 months and older, with very few exceptions. Pregnancy is not a contraindication. Older adults (older than 65 years) may benefit from the high-dose formulation.
People will buy a lottery ticket for a 1 in 100,000,000 chance to win; even with this year’s flu shot, there’s a 1 in 4-5 chance of a win, and essentially no downside. It’s a good idea from a personal standpoint, and it’s a public health responsibility.
What if you get the flu?
For those who can’t be convinced or who lack access, prompt (within 72 hours) postexposure prophylaxis with an antiviral agent may prevent infection. For those unlucky people who develop influenza, treatment with oseltamivir or zanamivir may shorten the illness; in severe cases, these antiviral agents may save lives. Current guidelines recommend administering these medications to all patients hospitalized with influenza, regardless of symptom duration.
For current, comprehensive point-of-care information on the diagnosis and treatment of influenza, including links to other relevant resources, see Elsevier’s Clinical Overview on Influenza, updated September 2017 for this year’s flu season, available on ClinicalKey.
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