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04.28.2019

WIW 2019: How #VaccinesWork, Part 3

Why do some vaccines require more than one dose?

There are four reasons that babies – and even teens or adults – who receive a vaccine for the first time may need more than one dose. For some vaccines (primarily inactivated vaccines), the first dose does not provide as much immunity as possible. So, more than one dose is needed to build more complete immunity. The vaccine that protects against the bacteria Hib, which causes meningitis, is a good example.

                For some vaccines, after a while, immunity begins to wear off. At that point, a “booster” dose is needed to bring immunity levels back up. This booster dose usually occurs several years after the initial series of vaccine doses is given. For example, in the case of the DTaP vaccine (which protects against diptheria, tetanus, and pertussis), the initial series of four shots that children receive as part of their infant immunizations help build immunity. But a booster dose is needed at 4 years through 6 years old. Another booster against these diseases is needed at 11 or 12 years of age. This booster for older children – and teens and adults, too – is called Tdap.

                For some vaccines (primarily live vaccines), studies have shown that more than one dose is needed for everyone to develop the best immune response. For example, after one dose of the MMR vaccine, some people may not develop enough antibodies to fight off infection. The second dose helps make sure that almost everyone is protected.

                Finally, in the case of flu vaccines, adults and children (6 months and older) need to get a dose every year. Children 6 months through 8 years old who have never gotten a flu vaccine in the past or have only gotten one dose in past years need two doses the first year they are vaccinated. Then, an annual flu vaccine is needed because the flu viruses causing disease may be different from season to season. Every year, flu vaccines are made to protect against the viruses that research suggests will be most common. Also, the immunity a child gets from a flu vaccination wears off over time. Getting a flu vaccine every year helps keep a child protected, even if the vaccine viruses don’t change from one season to the next.

Although you may think many of these diseases are rare in your area, they do circulate around the world and can be brought into all areas, putting unvaccinated children at risk. Even with advances in health care, the diseases that vaccines prevent can still be very serious – and vaccination is the best way to prevent them.

  • Naomi Naik is the Communications Intern for Shot@Life and started working with the campaign this month. As a campaign intern, she helps support our communications team efforts at events, on our website, and on our social media channels.