COVID-19 Vaccine vials
COVID-19 Vaccine vials
COVID-19 Vaccine vials

A One-Shot COVID-19 Vaccine

Featured Experts:

As progress continues in developing and administering coronavirus vaccines to fight the COVID-19 pandemic, a vaccine that only requires a single shot was authorized for use in late February 2021. The U.S. Food and Drug Administration (FDA) issued an emergency use authorization (EUA) for a Johnson & Johnson COVID-19 vaccine for people age 18 and older.

In April 2021, the Johnson & Johnson vaccine was temporarily paused while the FDA and the Centers for Disease Control and Prevention (CDC) investigated rare cases of  serious blood clots in women who had received that vaccine. After careful review, the FDA and CDC recommended that using the J&J COVID-19 vaccine could resume. Johns Hopkins Medicine followed CDC guidelines, temporarily pausing and then resuming use of the J&J vaccine. Learn more about how Johns Hopkins Medicine responded to the pause.

Lisa Maragakis, M.D., M.P.H., senior director of infection prevention, and Gabor Kelen, M.D., director of the Johns Hopkins Office of Critical Event Preparedness and Response, answer your questions about the one-shot COVID-19 vaccine.

Does Johns Hopkins Medicine recommend the Johnson & Johnson vaccine?

Yes, we recommend that everyone who is eligible (currently all people over the age of 16) get vaccinated with one of the 3 currently authorized COVID-19 vaccines, including the Johnson & Johnson vaccine. A rare but serious blood clot developed in a few cases out of more than 8 million J&J vaccines administered in the U.S., as of April 23, 2021. After careful review of these cases, the FDA and CDC determined that administration of the Johnson & Johnson vaccine could safely continue. We view all three available COVID-19 vaccines as highly efficacious for preventing serious disease, hospitalization and death from COVID-19.

The Johnson & Johnson vaccine has some advantages, including:

  • The vaccine requires only one shot, so you are protected earlier than with other currently available vaccines. You also do not have to deal with possible side effects associated with the second dose of the other vaccines.
  • Reports on the Johnson & Johnson vaccine show extremely high efficacy in preventing hospitalizations and deaths due to COVID-19 28 days after vaccination.
  • In clinical studies, the Johnson & Johnson vaccine worked at preventing infection with the U.K. and South African COVID-19 variants.
  • The Johnson & Johnson vaccine seems to reduce asymptomatic infections, which can spread the virus to others.

We, along with the CDC, encourage those interested in getting vaccinated to take any authorized vaccine that is available from any legitimate and authorized organization.

Warning Signs: TTS Blood Clot Symptoms

The Johnson & Johnson vaccine was paused when a rare but serious blood clot disorder called thrombosis with thrombocytopenia syndrome, or TTS, developed in a small number of people who had received the Johnson & Johnson COVID-19 vaccine.

  • Nearly all reports of this serious condition have been in adult women younger than age 50.
  • The risk of this adverse event is rare, occurring at a rate of about 7 per 1 million vaccinated women between 18 and 49 years old. For women 50 years and older and men of all ages, this adverse event is even rarer.
  • A review of all available data at this time shows that this vaccine’s known and potential benefits outweigh its known and potential risks.
  • However, women younger than age 50 should be aware of this rare adverse event and should know that other COVID-19 vaccines are available. Symptoms related to the rare blood clots are listed below.

Although very rare and treatable when diagnosed in time, TTS is serious. Get medical help immediately if you have any of these symptoms within 3 weeks of receiving the Johnson & Johnson coronavirus vaccine:

  • Severe or persistent headaches or blurred vision
  • Shortness of breath
  • Chest pain
  • Leg swelling
  • Persistent abdominal pain
  • Easy bruising or tiny blood spots under the skin near the injection site

Learn more about how Johns Hopkins Medicine responded to the pause.

Does Johns Hopkins consider the Johnson & Johnson vaccine any less effective than the Pfizer and Moderna vaccines?

No, all three of these vaccines are very good at preventing the most important COVID-19 outcomes, including severe infection, hospitalization and death. For this reason, Johns Hopkins Medicine considers them to be equally valuable. The reported efficacy of each vaccine cannot be compared directly to the others because the study design and conditions were different across the trials.  We encourage anyone who wants to be vaccinated to take any legitimate and authorized vaccines available to them.

Will I have the chance to choose which type of vaccination I receive, the Johnson & Johnson, Pfizer or Moderna vaccine?

All three FDA-authorized COVID-19 vaccines are being given at Johns Hopkins Medicine: Pfizer-BioNTechModerna and Johnson & Johnson. We regard all three as highly effective in preventing serious disease, hospitalization and death from COVID-19. People ages 16 and 17 can only have the Pfizer-BioNTech COVID-19 vaccine at this time, as this is the only vaccine currently authorized for this age group.

At some Johns Hopkins Medicine locations, we list the days which vaccine is offered. Only one type of vaccine is administered at each site on a given day. You can use this information to schedule vaccination with a preferred vaccine type, but you cannot choose which vaccine to receive on the day of your appointment.

Does the Johnson & Johnson vaccine work on coronavirus variants?

In clinical studies, the Johnson & Johnson vaccine was efficacious against the U.K. and South African COVID-19 variants. These variants were not circulating widely at the time of the clinical trials for the other vaccines.

What is a viral vector vaccine, and how does it work on the coronavirus?

The Johnson & Johnson vaccine is a viral vector vaccine. This is another difference between this shot and the Pfizer and Moderna vaccines, which use messenger RNA (mRNA) technology.

Viral vector vaccines take a harmless virus, known as a vector — which cannot cause disease or replicate — and load it with information that informs cells how to manufacture a look-alike, harmless part of the coronavirus. That part, the spike protein, cannot infect a person or cause COVID-19 illness by itself.

Once a person gets the shot, their cells receive the “directions” from the vector, telling them how to create copies of the spike protein. The cells then go to work and make them. As the spike proteins accumulate in the body, the immune system is alerted to their presence and creates antibodies and an immune reaction to fight them. After about four weeks, there is enough protection to fight off the coronavirus that has the spike protein, and prevent severe illness.

Viral vector vaccines have been created and used against infections since the 1970s. They have also been used in gene therapy to treat cancer. In addition, they have been used in studies for HIV and influenza. Some of the vaccines developed to fight the Ebola virus used this technology.

syringe close up - covid19 coronavirus vaccine

COVID-19 Vaccine

Get information and updates from Johns Hopkins Medicine.

Updated May 6, 2021