COVID-19 Vaccine Effectiveness

Are the COVID-19 vaccines effective at keeping me from getting sick?

COVID-19 vaccines are shown to be 86%-95% effective at preventing severe cases of the disease approximately 10-12 days after receiving the full recommended dose. That means a small number of vaccinated individuals (5-15%, or 1-2 in 20) could still be infected with and spread COVID-19 even after receiving the full-recommended dosage. But there’s good news: vaccinated individuals typically see a less severe form of the disease. These rare cases are why continuing to ACT (wearing a mask, social distancing, and washing hands often) is so important even among vaccinated individuals until larger herd immunity is achieved.

Learn more about how COVID-19 vaccines work.

Will more than one dose of COVID-19 vaccine be required?

Current COVID-19 vaccines approved by the FDA or authorized for emergency use in the United States require either one dose (Johnson & Johnson) or two doses (Pfizer or Moderna) to achieve optimum immunity levels. If you are receiving a two-dose vaccine, it is very important that you get both doses within the required time frame to ensure the best protection from COVID-19.

The one-dose vaccine seems to be less effective than the two-dose vaccines. And no vaccine is 100% effective. Should I be worried?

Vaccines that aren't showing 100% efficacy should not be cause for alarm. No vaccine is 100% efficacious and the COVID-19 vaccines currently available are actually more effective compared to other vaccines we routinely receive in the United States.  They all do an excellent job of preventing severe forms of the disease, including hospitalizations and mortality, which is the primary goal of any vaccine.

The Janssen (Johnson & Johnson) COVID-19 vaccine showed 66% efficacy across all regions where it was studied (the U.S., South Africa, and Latin America) and showed to be 85% effective at preventing severe disease/hospitalization and 100% effective at preventing death. So this vaccine, much like the two-dose vaccines currently available, is extremely effective at preventing severe COVID-19 complications such as hospitalization and death.

Typical Vaccine Effectiveness

By comparison, our flu vaccine effectiveness is typically 40-60%. These percentages vary from season to season because of different strains of flu circulating in any given year. Even at 60% efficacy, the flu vaccine is considered the standard of care for preventing both influenza spread and severe complications such as death. Additionally, these clinical trials were conducted in different geographic areas and at different points in time when transmission rates and the presence of variants differed. For these reasons, you cannot compare the efficacy rates of one COVID-19 vaccine to another.

Other Factors

Efficacy is only one factor that makes a good vaccine. Others include supply, logistic hurdles, and resource allocation. A one-dose vaccine requires far fewer resources as there is no follow-up for a second dose. Johnson & Johnson is expected to produce one billion vaccine doses by the end of 2021. This means one billion people across the world could receive a one-dose vaccine that is 66% percent effective by 2022. This is a huge step toward ending the pandemic, as experts believe 70% of the population should be vaccinated to achieve herd immunity.

COVID-19 Vaccine Effectiveness

All three vaccines are incredibly effective. Getting any of the available COVID-19 vaccines will protect you and the ones you love from this deadly disease.

Are current COVID19 vaccines effective against different strains?

COVID-19 virus mutations are expected. Some variants may be more transmissible or less responsive to vaccines, so it is important to avoid exposure. Scientists will continue monitoring variants of the virus and will assess the related efficacy of current vaccines. It is likely vaccine manufacturers will modify future vaccines to provide immunity to more than one strain, if necessary. 

It is important for eligible individuals to receive a vaccine as quickly as possible to help communities achieve herd immunity. This provides less opportunity for the COVID-19 virus to mutate into variants. To date, current vaccines appear to be effective against variants but we cannot predict if that will remain true if the virus continues to mutate into additional variants.

Where can I learn more about different vaccines?

The U.S. Centers for Disease Control & Prevention updates its COVID-19 vaccine pages regularly. Visit the link below for updated information on authorized and recommended vaccines as they become available in the United States. 

Information includes:

  • Who is and is not recommended to receive each vaccine
  • Side effects
  • Information from clinical trials, including study design and outcomes
  • How each vaccine works
  • What to expect after vaccination
  • Vaccine ingredients, and more
Visit the CDC