How effective is the Flu Vaccine in 2017/2018?
How effective is the flu vaccine?
CDC conducts studies each year to determine how well the influenza (flu) vaccine protects against flu illness. While vaccine effectiveness can vary, recent studies show that flu vaccination reduces the risk of flu illness by between 40% and 60% among the overall population during seasons when most circulating flu viruses are well-matched to the flu vaccine. In general, current flu vaccines tend to work better against influenza B and influenza A(H1N1) viruses and offer lower protection against influenza A(H3N2) viruses. See “Does flu vaccine effectiveness vary by type or subtype?” and “Why is flu vaccine typically less effective against influenza A H3N2 viruses?” for more information.
What are factors that influence how well the vaccine works?
How well the flu vaccine works (or its ability to prevent flu illness) can range widely from season to season. The vaccine’s effectiveness also can vary depending on who is being vaccinated. At least two factors play an important role in determining the likelihood that flu vaccine will protect a person from flu illness: 1) characteristics of the person being vaccinated (such as their age and health), and 2) the similarity or “match” between the flu viruses the flu vaccine is designed to protect against and the flu viruses spreading in the community. During years when the flu vaccine is not well matched to circulating influenza viruses, it is possible that no benefit from flu vaccination may be observed. During years when there is a good match between the flu vaccine and circulating viruses, it is possible to measure substantial benefits from flu vaccination in terms of preventing flu illness. However, even during years when the flu vaccine match is good, the benefits of flu vaccination will vary, depending on various factors like the characteristics of the person being vaccinated, what influenza viruses are circulating that season and even, potentially, which flu vaccine was used.
Each flu season researchers try to determine how well flu vaccines work as a public health intervention. Estimates of how well a flu vaccine works can vary based on study design, outcome(s) measured, population studied and the season in which the flu vaccine was studied. These differences can make it difficult to compare one study’s results with another’s.
While determining how well a flu vaccine works is challenging, in general, recent studies have supported the conclusion that flu vaccination benefits public health, especially when the flu vaccine is well matched to circulating flu viruses.
What are the benefits of flu vaccination?
While how well the flu vaccine works can vary, there are many reasons to get a flu vaccine each year.
Flu vaccination can keep you from getting sick with flu.
Flu vaccination can reduce the risk of flu-associated hospitalization, including among children and older adults.
Vaccine effectiveness for the prevention of flu-associated hospitalizations was similar to vaccine effectiveness against flu illness resulting in doctor’s visits in a comparative study published in 2016.
Flu vaccination is an important preventive tool for people with chronic health conditions.
Flu vaccination has been associated with lower rates of some cardiac (heart) events among people with heart disease, especially among those who experienced a cardiac event in the past year.
Flu vaccination also has been associated with reduced hospitalizations among people with diabetes (79%) and chronic lung disease (52%).
Flu vaccination helps protect women during and after pregnancy. Getting vaccinated against the flu can also protect a baby from flu after birth. (A mother can pass antibodies onto the developing baby during pregnancy.)
A study that looked at flu vaccine effectiveness in pregnant women found that vaccination reduced the risk of flu-associated acute respiratory infection (ARI) by about one half.
There are studies that show that vaccination of pregnant women can reduce their baby’s risk of flu illness by up to half. This protective benefit was observed for up to four months after birth.
Flu vaccination also may make your flu illness milder if you do get sick.
Getting vaccinated also protects people around you, including those who are more vulnerable to serious flu illness, like babies and young children, older people, and people with certain chronic health conditions.
Is the flu vaccine effective against all types of flu and cold viruses?
Seasonal flu vaccines are designed to protect against infection and illness caused by the three or four influenza viruses (depending on vaccine) that research indicates will be most common during the flu season. “Trivalent” flu vaccines are formulated to protect against three flu viruses, and “quadrivalent” flu vaccines protect against four flu viruses. Flu vaccines do NOT protect against infection and illness caused by other viruses that can also cause flu-like symptoms. There are many other viruses besides flu viruses that can result in flu-like illness* (also known as influenza-like illness or “ILI”) that spread during the flu season. These non-flu viruses include rhinovirus (one cause of the “common cold”) and respiratory syncytial virus (RSV), which is the most common cause of severe respiratory illness in young children, as well as a leading cause of death from respiratory illness in those aged 65 years and older.