Is One Shot Enough? Understanding Vaccine Dosing

Vaccines imitate an infection, triggering an immune system response that helps the body effectively defend itself when it is exposed to the infection in future. In the late 19th century, smallpox, cholera, and typhoid were among the first diseases to have vaccines developed. As vaccinology has advanced, the US government has passed legislation to standardize and regulate vaccine development, including the Biologics Control Act and the formation of the National Institutes of Health. This increased oversight has contributed to important immunization discoveries, including proper dosages for each unique vaccine to maximize their effectiveness.

Why Some Vaccines Require Multiple Doses

When a vaccine is administered, the immune system remembers the infection and produces antibodies to prevent future infections from the same disease. There are several different types of vaccines, each triggering a different immune response. While immunity for some diseases can be achieved with a single vaccine dose, factors like disease mutations, immune system health, length of inoculation period, and vaccine type impact the overall protection the vaccine provides and can create a need for two or more vaccine doses to achieve optimal outcomes.

Live-attenuated Vaccines

Live-attenuated vaccines contain a weakened version of a virus, and often only require one or two doses to provide protective immunity. They are similar enough to the virus they are fighting to produce a strong and lasting immune response. The first live-attenuated vaccines were developed by Louis Pasteur in the late 19th century for rabies and chicken cholera. Today, live-attenuated vaccines help protect against illnesses like smallpox, rotavirus, measles, mumps, and rubella.

Subunit, Recombinant, Polysaccharide, and Conjugate Vaccines

Subunit, recombinant, polysaccharide, and conjugate vaccines are used to combat diseases like HPV, hepatitis B, and shingles, and require multiple doses. These vaccines use a small portion of the disease’s germ, allowing even patients who are at higher risk to receive these immunizations. Due to the small size of the virus sample that is used, additional booster shots may be needed to maintain lifelong immunity. The CDC recommends two doses of the shingles vaccine for adults fifty years or older. Hepatitis B is administered across a three-dose series, starting as early as infancy, and HPV is recommended as a two-dose series available from ages nine through twenty-six.

Inactivated Vaccines

Inactivated vaccines use dead samples of a germ, but do not typically provide the same level of protection as live vaccines. When a vaccine does not contain a live form of the virus, coverage can wane over time. As a result, multiple doses are needed in the form of booster shots or seasonal vaccinations to support and maintain the immune response. Some of the more common illnesses that can be prevented with inactivated vaccines include influenza, polio, and hepatitis A. The CDC recommends four doses by age six for the inactivated polio vaccine (IPV) and two doses administered six months apart for the hepatitis A vaccine (HepA). Influenza follows a seasonal vaccination schedule, which helps fight diseases that frequently mutate or become more prevalent during certain times of year.

Toxoid Vaccines

Toxoid vaccines contain toxins that are produced by disease-causing germs, meaning the immune response is triggered by toxins rather than the germ itself. These vaccine types are used to treat diphtheria and tetanus, requiring multiple doses to achieve immunity.

Staying Up to Date

The best way to ensure patients achieve full vaccine effectiveness is to follow the recommended routine immunization schedules. Providers play an important role in educating patients about routine vaccinations and helping them stay on track with their immunizations.