The number of booster shots you need depends on which vaccine you’re talking about. For COVID-19, the current approach has shifted away from stacking multiple boosters and now centers on a single updated dose each year for most people. Other routine vaccines like tetanus require a booster every 10 years, while some vaccines like shingles and pneumococcal need no boosters at all after the initial series.
COVID-19 Boosters: A Simpler System Now
The early years of COVID-19 vaccination involved a primary series (two shots for Pfizer or Moderna, one for Johnson & Johnson) followed by one or more booster doses as new variants emerged. Between 2021 and 2023, many people received two, three, or even four total boosters on top of their original series. That layered approach created a lot of confusion, and the system has since been simplified.
Starting with the 2024-2025 season and continuing into 2025-2026, the CDC moved to a model that looks more like the annual flu shot. For most people ages 5 through 64, the recommendation is one updated dose of the current season’s vaccine, regardless of how many shots you’ve had before. If you’ve never been vaccinated against COVID-19, you still need just one dose to start.
Two groups need more than one dose. Adults 65 and older are recommended to get two doses of the updated vaccine, spaced apart, whether or not they’ve been previously vaccinated. Young children between 6 and 23 months who haven’t been vaccinated yet also need two doses to build adequate protection. Children ages 2 and up follow the same one-dose pattern as adults.
Extra Doses for Weakened Immune Systems
People who are moderately or severely immunocompromised, such as organ transplant recipients or those on certain medications that suppress the immune system, can receive additional doses beyond what’s recommended for the general population. After completing their initial series or updated dose, they may get another dose at least two months later, based on a conversation with their doctor. There’s no hard cap on the number of extra doses for this group; the decision is individualized based on how well their immune system responds.
Tetanus and Pertussis: Every 10 Years
The tetanus-diphtheria-pertussis vaccine is the classic example of a lifelong booster schedule. After the childhood series, adults need a booster every 10 years for the rest of their lives. That means someone who lives to 80 could receive six or seven boosters during adulthood alone. If you get a deep or dirty wound, the timeline shortens to five years since your last dose.
Pregnant women are a special case. A dose is recommended during every pregnancy, typically in the early part of the third trimester, to pass protective antibodies to the newborn. This applies even if the last booster was recent.
Vaccines That Don’t Need Boosters
Not every vaccine requires ongoing boosters. Several common immunizations are considered complete after a defined series of shots.
- Shingles: Two doses, given 2 to 6 months apart, for adults 50 and older. No booster is currently recommended after that. If you’re immunocompromised, the second dose can be moved up to as early as one month after the first.
- MMR (measles, mumps, rubella): One or two doses for adults born in 1957 or later, depending on risk factors. No boosters needed.
- Chickenpox: Two doses for adults born in 1980 or later who haven’t had the disease. No boosters after that.
Pneumococcal Vaccines for Older Adults
Pneumococcal vaccines protect against bacterial pneumonia and are recommended for adults 50 and older. The number of shots depends on which vaccine you receive. If you get PCV20 or PCV21 (the newer options), you need just one dose and you’re done. If you get PCV15 instead, you’ll need a follow-up dose of a different pneumococcal vaccine about a year later. Either path, there are no recurring boosters.
Why the Word “Booster” Gets Confusing
Part of the confusion around booster counts comes from the term itself. In vaccine science, a “booster” is a dose given after the primary series has already built immunity, meant to strengthen or extend that protection over time. An “additional primary dose,” by contrast, is an extra shot given to people whose immune systems didn’t respond well enough to the original series. During 2021 and 2022, both types of doses were being recommended for different groups at the same time, which muddied the public conversation considerably.
The current COVID-19 framework sidesteps this issue by treating each season’s updated vaccine as a single recommendation rather than labeling doses as “third booster” or “fourth booster.” For most adults, the practical answer is now straightforward: one updated COVID shot per year, a tetanus booster every decade, and a handful of other vaccines that are one-and-done after their initial series.