Skip to main content

COVID-19 vaccines and variants: What you should know

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on April 7, 2021.

Official answer


Which coronavirus variants are in the U.S.?

Several coronavirus (SARS-CoV-2) mutations (variants) have become clinically important in the U.S since the fall of 2020, and include:

  • B.1.1.7 (UK variant), first detected in the UK in Sept. 2020 and in the U.S. in Dec. 2020. Over 15,000 cases with B.1.1.7 have been reported in the U.S through surveillance. B.1.1.7 is spreading rapidly and has been detected in every U.S. state.
  • B.1.351 (South Africa variant), first detected in South Africa in October 2020 and in the U.S. in Jan 2021. Over 370 cases of B.1.351 have been reported in the U.S.
  • P.1 (Brazil variant), initially identified in travelers from Brazil, who were tested during routine screening in Japan in January 2021. The P.1 variant was first detected in the U.S. in Jan 2021. Over 280 cases of P.1 have been reported in the U.S.
  • B.1.427 and B.1.429 variants, first identified in California in February 2021.

These numbers do not represent the total number of variants in the U.S. In the U.S., sequence-based strain surveillance is ongoing in academic, state and public health government institutions. Other variants are currently circulating worldwide, and new variants may occur over time.

How dangerous are the coronavirus COVID-19 variants?

All viruses can mutate which leads to changes in their internal genetic code, creating "variants." Mutations are an expected part of the virus life-cycle, and not all variants are dangerous or harmful.

Scientists are researching how the new variants may alter COVID-19 disease, natural immunity, and the effect on vaccine effectiveness.

  • Some mutations of the coronavirus have been shown to be more contagious or to cause more serious COVID-19 illness. In January 2021, researchers in the UK reported that B.1.1.7 variant may cause an increased risk of death compared to other variants, but more studies to prove this effect are needed as reported by the CDC.
  • Variants may affect the effectiveness of the COVID-19 vaccines. Experts state that the virus would need to develop multiple mutations in the spike protein to evade immunity induced by vaccines or by natural infection.
  • A person's natural immunity from a previous COVID-19 infection could be affected by variants. This could lead to a spike in new cases, although experts think this in unlikely to occur.
  • Variants theoretically may also alter treatments for COVID-19 such as monoclonal antibodies and the results of lab tests used to detect the virus or antibodies.

How do mutations affect vaccines?

Mutations can make vaccines hard to develop because of the change of the genetic footprint of the virus. Viruses often naturally mutate.

One example is the flu vaccine. New strains of influenza often appear worldwide each year, and those strains are incorporated into a new vaccine each flu season. Because the influenza vaccine gets a reboot each year, and it’s protective effect wanes over time, you need a yearly vaccine for protection against influenza.

But other viruses do not mutate so quickly. For example, the measles is slow to mutate. To protect yourself or your child from measles, one set of shots, typically given in childhood, is protective for a lifetime.

COVID-19 is a highly contagious viral infection due to the SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) virus. The coronavirus is a long virus microscopically with 30,000 nucleotides and is twice the size of the flu virus. Coronavirus is an RNA virus, as are the flu and measles virus. Variants appear to have developed mutations in the spike protein of the coronavirus. The spike protein is the part that helps the virus to attach to infect human cells.

As of now, studies suggest that vaccination with the currently available vaccines in the U.S. recognize these SARS-CoV-2 variants. As the SARS-CoV-2 virus mutates over time, vaccines updates or boosters may be needed. Scientists are rapidly investigating how variants may affect the vaccines and if booster shots will be needed.

Which COVID-19 vaccines are available in the U.S.?

In December 2020, Pfizer / BioNTech's BNT162b2 and Moderna's mRNA-1273 COVID-19 vaccines were given Emergency Use Authorization (EUA) by the FDA. In studies, the vaccines were found to be 94% to 95% effective in preventing COVID-19 disease.These vaccines require two shots, given 3 or 4 weeks apart depending upon the vaccine. The Pfizer vaccine is used in people 16 years and older, while the Moderna vaccine is for adults at least 18 years old.

In February 2021, Janssen's single dose COVID vaccine also received EUA for adults 18 years and older and demonstrated a 66% to 67% effectiveness against COVID disease. It is not made with mRNA technology but with an adenovirus vector.

People are not considered fully protected until two weeks after their final shot. Getting vaccinated is a crucial step in protecting yourself and others from COVID-19 disease, in addition to wearing a mask and social distancing. Guidelines are available from the CDC on how to protect yourself and others after you've been fully vaccinated.

Children 12 to 15 years

A study in 2,260 adolescents 12 to 15 years of age released by Pfizer-BioNTech at the end of March 2021 states that their vaccine (BNT162b2) showed a 100% efficacy rate and robust antibody response to COVID-19. The vaccine was also well-tolerated. In the trial, 18 cases of COVID-19 were observed in the placebo group (n=1,129) versus none in the vaccinated group (n=1,131). The companies will submit data to the FDA to seek emergency use authorization, and to other regulators worldwide.

How do the mRNA vaccines work?

The messenger RNA (mRNA) vaccines encode a form of the spike (S) protein of SARS-CoV-2 virus. The vaccine teaches the cells to make a piece of the spike protein, which triggers an immune response to help prevent illness if later exposed to the virus. The partial piece of the spike protein cannot cause COVID-19 disease.

  • The dose for the Pfizer / BioNTech vaccine (for patients 16 years of age and older) is a series of two intramuscular (IM) injections in the upper arm given 3 weeks (21 days) apart.
  • The Moderna vaccine (for patients 18 years of age and older) is also a 2-dose series, but separated by 4 weeks (28 days). After administration, you’ll need to stay where you received the vaccine for 15 to 30 minutes for observation.

Commonly reported side effects with mRNA vaccines include injection site pain or swelling and flu-like symptoms such as fever, chills, tiredness, muscle and joint pain, and headache. These side effects subside in 24-48 hours in most patients. In some cases, side effects may be worse after the second dose than the first dose.

Severe allergic reactions (anaphylactic reactions) are rare but have been reported. These reactions can be treated, and most patients with allergies can still get the vaccine. It is recommended you do not use the vaccine if you have had a severe allergic reaction to any of the ingredients in the vaccine you receive, or to a previous dose of the vaccine.

How does the adenovirus vector vaccine work?

In Feb 2021, the FDA has issued an emergency use authorization (EUA) for the Janssen COVID-19 Vaccine, the third vaccine in the U.S. for the prevention of COVID-19 disease. The Janssen COVID-19 Vaccine is used in individuals 18 years of age and older, is given as a one-time shot, and can be shipped and stored under refrigeration.

The new vaccine is manufactured differently than the mRNA vaccines from Moderna and Pfizer / BioNTech: it uses the adenovirus type 26 (Ad26), a weakened cold virus to deliver DNA to temporarily make the “spike” protein of the SARS-CoV-2 virus. It does not cause COVID disease or a cold but helps to trigger the immune response against the SARS-CoV-2 virus.

  • In the ongoing Phase 3 ENSEMBLE studies from South Africa, Latin America and the U.S, over 44,000 participants aged 18 years and older received the vaccine or saline placebo and were followed for a median of 8 weeks.
  • Across geographies, the vaccine was approximately 66.9% effective in preventing moderate to severe/critical COVID-19 two weeks after vaccination and 66.1% effective in preventing moderate to severe/critical disease four weeks after vaccination. Vaccine efficacy against severe/critical COVID-19 at least 14 days after vaccination was 76.7% and 85.4% at least 28 days after vaccination.
  • None of the nearly 22,000 vaccinated people in the trial died of COVID-19 compared to five deaths in the placebo group.

Side effects were mild to moderate and usually cleared up in 1 to 2 days. The most commonly reported side effects were injection site pain, headache, fatigue, muscle aches, and nausea.

How long does the COVID vaccine last?

COVID-19 is still spreading rapidly throughout the U.S. The duration of protection from the vaccines is not fully known yet, but Pfizer / BioNTech and Moderna have reported in April 2021 that immunity lasts at least 6 months with their vaccine. Pfizer has noted that their vaccine remains up to 91% effective with no safety concerns.

Current guidelines to prevent the spread of COVID-19 in the public should still be followed after vaccination:

  • wear a mask
  • maintain 6 feet of distance
  • avoid crowds
  • wash your hands frequently.

Related medical questions

Related support groups