Coronavirus Prevention: Vaccines, Isolation, and Quarantine

Diana Zuckerman, Ph.D., Thomas Eagen, Ph.D., Meg Seymour, Ph.D., Sophia Phillips, M.S., Avni Patel, Angelica Estrada

Updated December 15, 2022

What about the vaccines?

The COVID-19 vaccines that have been authorized or approved in the U.S. are designed to prevent serious illness, hospitalization, and death due to the virus. They are not 100% effective and some people who are fully vaccinated have become infected, sometimes called a breakthrough infection. These individuals have usually experienced mild illness, but some have become seriously ill.

On August 23, 2021, the Food and Drug Administration (FDA) approved Pfizer’s COVID-19 vaccine, which is now called Comirnaty, for the prevention of COVID-19 disease in individuals 16 years of age and older. This mRNA vaccine initially required two doses separated by 21 days, but as of late February 2022 the second dose is recommended to be 8 weeks later if possible, because immunity will last longer. The two-dose vaccine is also available under emergency use authorization (EUA) for children 5 years or older. Anyone ages 12 and older is encouraged to get a third “booster” dose.

On January 31, 2022, the FDA approved Moderna’s COVID-19 vaccine (now called Spikevax) for adults ages 18 and older. It also uses mRNA technology and initially included two doses administered 28 days apart, but as of late February 2022 is recommended to be 8 weeks apart if possible, because immunity will last longer. Boosters will be discussed in more detail below.

Two other vaccines are authorized for adults ages 18 and older under the FDA’s emergency use authorization (EUA).  That includes the vaccine made by Janssen, a subsidiary of Johnson & Johnson. It is a single-dose vaccine, using an adenovirus instead of mRNA technology, and it is available under EUA. However, as of May 5, 2022, the FDA is restricting its Emergency Use Authorization to only include adults 18 and older who are not able to obtain or use either of the other two vaccines. In July 2022, the FDA authorized a 2-dose vaccine made by Novavax.  As the newest vaccine, less is known about its long-term safety or effectiveness.

In March 2022, FDA declined to grant EUA for the Covaxin COVID-19 vaccine for use in children ages 2 to 18 years.

As of October 20, 2022, approximately 68% of the entire U.S. population fully vaccinated (recieving both primary doses). Additionally, 34% of the U.S. population is boosted. Rates of vaccination differ greatly by state and demographic traits.

As noted above, the Moderna and Pfizer vaccine are considered safer and more effective than the Johnson & Johnson vaccine. Nevertheless, all three vaccines have been shown to be effective at preventing serious illness from COVID-19. The vaccines are less effective for older people and those with a compromised immune system, such as those with organ transplants that take drugs to prevent organ rejection. While the initial studies of the three vaccines included few people under 18, pregnant women, people with compromised immune systems, or those with serious allergies, a study published in May 2021 in JAMA indicated that the vaccine has benefits that outweigh the risks for these individuals.

A major question is how long does the immunity from the vaccines last? In October 2021, FDA authorized a third primary dose of the Pfizer-BioNTech and Moderna vaccines under an EUA for individuals who are immunocompromised.  This should be administered 6 months after the second dose. As of January 5, 2022, booster doses of the Pfizer vaccine are recommended for anyone ages 12 and older, and of the Moderna vaccine for anyone ages 18 and older.  Both boosters should be given at least 5 months after their second dose. Although available for all adults, the CDC specifically recommends the booster for adults ages 50 and older. The booster dose of the Moderna vaccine is 1/2 the dose of the primary two doses, while the Pfizer booster dose is identical to the two previous doses. The CDC also recommends that adults 18 and older who received the Johnson & Johnson vaccine at least 2 months ago should get a booster shot.

A 2022 study, however, concludes that there is limited evidence that the vaccine is effective for children, particularly those aged 5-11 years. The study reports that vaccine efficacy declines overtime, and may be ineffective past the 34 day mark. While worrisome, this study does not negate the complete effectiveness of the vaccine, and experts still advise that children aged 5-11 years be vaccinated as it provides essential protection against severe cases of COVID-19. The results of the study highlight the need for alternative vaccine dosing schedules to ensure more layers of protection.

In October 2022, a study published in JAMA described the health outcomes of 1.6 million people served by the Veterans Health Administration (VA) who were fully vaccinated for COVID-19, including a booster shot. About 75% of those identified were 65 and older and more than 70% had a pre-existing health condition that put them at greater risk of severe COVID-19 infection. During the 24-week follow-up, only one in 1,000 (0.1%) were hospitalized with COVID or died. Even among those who were immunocompromised, less than one-third of 1% (one in 300) were hospitalized or died. For healthy adults over 65, the chance of hospitalization or death was 0.02% (2 out of 10,000). While there was no control group in this study and the study population was primarily men, it demonstrates the life-saving impact of full vaccination with boosters.

The FDA has also authorized “mixing and matching” vaccines for booster doses. For example, someone who got the Johnson & Johnson vaccine could get a booster dose of the Moderna (half dose) or Pfizer-BioNTech vaccines at least 2 months after their initial dose, or someone who got both primary doses of the Moderna vaccine could get a booster dose of the Pfizer-BioNTech vaccine 5 months after completing their two doses of Moderna.

It is important that anyone getting vaccinated is told about potential risks. Common side effects from the vaccines include: pain, redness, and swelling on the arm where you receive the shot; and tiredness, headache, muscle pain, chills, fever, and nausea throughout the rest of your body. Most side effects last only one day, and are typically stronger following the second dose of Pfizer or Moderna. In April 2021, there was a temporary pause to the use of the Johnson & Johnson vaccine after reports of rare blood clots, primarily in adult women younger than 50 years old. Following a review of the data, the FDA added a warning label to the vaccine about these rare blood clots. In December 2021, the CDC recommended that the Pfizer and Moderna vaccines be the preferred choice over the Johnson & Johnson vaccine, due to the risk of blood clots. However, the Director of the CDC, Dr. Rochelle Walensky, noted that despite the risk, “any vaccination is better than no vaccination” because the side effects are much less severe than the risks of COVID-19.

Sweden, Denmark, and Finland have paused the use of the Moderna vaccine in young people, due to the risk of myocarditis (inflammation of part of the heart muscle) and pericarditis (inflammation of the tissue around the heart), particularly in young men. However, one study found a 16 times higher risk of myocarditis among patients with COVID-19 compared to those without.

Some people are allergic to one or more of the ingredients of COVID-19 vaccines, and some people with compromised immune systems will find the vaccine is much less effective for them compared to people with well-functioning immune systems. In December 2021, the FDA issued an EUA for a new AstraZeneca monoclonal antibody drug called Evusheld, which is intended for those ages 12 and older who have compromised immune systems, such as those with cancer. The drug (taken as two injections) contains laboratory-made antibody proteins, and is intended to help reduce the risk of COVID-19 infection for up to 6 months. The FDA is careful to note that this drug is not a substitute for vaccination, which is the best form of protection from infection. Instead, Evusheld is meant to help provide protection to those who have a compromised immune system that makes them even more vulnerable to infection.

With the rise of variants that have increasing rates of infection, some vaccine manufacturers have been working on booster’s that directly target current strains of the coronavirus.

On August 15, 2022, The U.K. became the first to authorize a vaccine that targets both the original COVID-19 virus from 2020 as well as the increasingly common Omicron BA.1 variant. The vaccine made by Moderna was approved by Britain’s Medicines and Healthcare products Regulatory Agency and their scientific advisory body, the Commission on Human Medicines. The booster, Spikevax bivalent Original/Omicron, is 50 micrograms, with half dedicated to each strain. It had side effects similar to the original Moderna booster dose.

A week later on August 22, 2022, Pfizer and BioNTech followed suit in in the U.S., submitting an Emergency Use Authorization for their Omicron BA.4/BA.5 bivalent vaccine for people 12 and older. On August 31, 2022 the FDA approved the amended EUA for the Moderna and Pfizer-BioNTech COVID-19 bivalent vaccines as a single use booster at least two months following a primary or booster dose. As of December 8, 2022 the Moderna and Pfizer-BioNTech COVID-19 Bivalent is authorized for individuals 6 months or older.

The U.S. Department of Health and Human Services and the U.S. The Department of Defense purchased 66 million doses of Moderna’s vaccine in addition to the previous 105 million bivalent COVID-19 boosters from Pfizer the U.S. purchased earlier this year. Bivalent vaccines are looking to become the norm however, as the Food and Drug Administration’s Vaccine Advisory Committee voted to require an Omicron component in this upcoming 2022 season’s booster dose.

In addition to the bivalent vaccine booster, the CDC authorized the Novavax monovalent booster for adults 18 years and older as a third dose six months post completion of the primary series. This dose is available to those who had the Novavax, Pfizer, Moderna, or Johnson & Johnson primary shots. This authorization provides a booster option to individuals who cannot or will not receive mRNA boosters/vaccines.

Can children be vaccinated against COVID-19?

The short answer is, yes! The FDA has authorized the emergency use of the Pfizer and Moderna vaccine for children 6 months through 5 years, and 5 years through 11 years.  The FDA reviewed the data on the studies of children taking the vaccines and consulted an independent Vaccine Advisory Committee before making the decision.

Vaccines for Children between the ages of 6 months and 5 years

As of June 17, 2022, the Moderna and Pfizer vaccines are authorized for the prevention of COVID-19 disease in children ages 6 months and older. Although the COVID vaccines do not always prevent infections in children or adults, they are expected to protect against severe illness and death.

The Moderna COVID-19 vaccine is administered to children ages 6 months to 5 years in two doses, one month apart. A third dose is administered at least one month after the second dose for immunocompromised children. The Pfizer-BioNTech COVID-19 vaccine is administered to all children ages 6 months to 5 years in three doses. The initial two doses are administered three weeks apart, and the third is administered at least eight weeks after the second dose.  All doses of both vaccines are lower than the doses for adults.

Effectiveness and Safety of the Moderna COVID-19 Vaccine

In two ongoing, blinded, and randomized clinical trials, the vaccine was 51% effective in preventing COVID-19 infection in children 6-23 months, and 37% effective for children between 2 and 5 years of age. The most commonly reported side effects for children between 6 months and 5 years were: pain, redness and tenderness/ swelling at the injection site, and fever. In children between 6 and 36 months, commonly reported side effects were crying, irritability, sleepiness, and loss of appetite. For example, 11% of children 6-23 months experienced any fever after the first dose, and almost 15% experienced any fever after the second dose. Children 37 months and older experienced fatigue, nausea, headache, muscle aches, chills, and joint stiffness. Fatigue was very common, with 48% of children 37 months-5 years experiencing any fatigue after the second dose.

Effectiveness and Safety of the Pfizer-BioNTech COVID-19 Vaccine

Studies show that the immune response to this vaccine in children ages 6-23 months and 2-4 years is comparable to the immune response of older participants. The most commonly reported side effects in these age groups are irritability, decreased appetite, fever, and tenderness/swelling at the injection site. For example, 51% of children ages 6-23 months experienced any irritability after the first dose, and 47% experienced any irritability after the second dose. In vaccine recipients aged 2-4 years, additional side effects included fever, headache, and chills.

Since the side effects were expected to be short-term, the FDA decision to authorize the vaccines for children and adults was based on just a few months of safety data.  As was the case for adults, safety monitoring of the vaccines for children is ongoing.

Vaccines for Children between the ages of 5 and 11 years

On October 29, 2021, the FDA approved the emergency use of the Pfizer-BioNTech vaccine for the prevention of COVID-19 disease in children ages 5 through 11 years. This vaccine is administered in 2 doses, 3 weeks apart, at a lower dose than the vaccine for adults.

Effectiveness and Safety of the Pfizer-BioNTech COVID-19 Vaccine

 The vaccine was 91% effective in preventing severe COVID-19 infection in children 5 through 11. An ongoing, randomized study of approximately 4,700 children ages 5 through 11 years is being conducted in the U.S., Finland, Poland, and Spain. The FDA compared the immune response of 264 children in this age group and compared them with the immune responses of participants ages 16 through 25, determining that the immune responses in children were similar to the older participants.

The vaccine’s safety was studied in an ongoing clinical trial of approximately 3,100 children ages 5-11. In addition, 1,444 participants were monitored for safety at least 2 months after the second dose.  Commonly reported side effects included: “injection site pain (sore arm), redness and swelling, fatigue, headache, muscle and/or joint pain, chills, fever, swollen lymph nodes, nausea and decreased appetite”. More children reported side effects after the second dose.  For example, 34% of children ages 5 through 11 experienced any fatigue after the first dose, and 39% experienced any fatigue after the second dose.  Fewer than 1% experienced more severe side effects, such as developing a rash or swelling triggered by an allergy. Almost all of the side effects reported went away within one to two days and were described as generally mild to moderate in severity.

How can I protect myself and others?

If you live in the U.S., the best way to protect yourself and others it to get one of the 3 vaccines available. The vaccines are widely available throughout the U.S. in multiple locations from community health centers to local pharmacies. Treatment options for COVID-19 do not cure the virus but FDA has designated treatments can help prevent hospitalization and death. The FDA has approved one drug treatment for COVID-19 and granted EUAs for 12 drug treatments, two of which were later rescinded. However, several of the remaining 10 treatments are now rarely used. Details about available treatments are described here.

What if you are pregnant?  Research shows that COVID infection is dangerous to pregnant women and that vaccinating pregnant women is safe.  For example, a study of more than 24,000 newborns, of whom almost 17,000 were exposed to a mRNA COVID vaccine in the first or second trimesters when their mothers were vaccinated, found no differences in preterm birth rates, neonatal hospitalizations, congenital abnormalities or infant mortality.  A small study found that most infants born to COVID-vaccinated mothers had persistent antibodies at 6 months, compared with infants born to mothers who had been infected with SARS-CoV-2.

In contrast to vaccination, a COVID infection increases the chances of serious harm for pregnant women.  A retrospective study of more than 14,000 pregnant women found that those with COVID infections were more likely to die or have serious illness related to hypertensive disorders of pregnancy, postpartum hemorrhage, or infection other than SARS-CoV-2 compared to pregnant women who did not have a COVID infection (13% vs 9%).  All 5 maternal deaths in the study were women who were infected with COVID.

What else can I do to stay safe?

In addition to getting vaccinated, you can amend behaviors and limit certain types of interactions for extra protection from COVID-19:

  • Avoid spending time with others if you or any of them have symptoms of COVID-19.
  • For people who have tested positive for COVID-19 and have no symptoms at all, the CDC recommends (as of August 11, 2022) you isolate for at least five days. Day 0 starts the day you were tested, and day 1 is your first full day after you were tested. If you have to go in public, only go places where you are able to wear a high-quality mask. You should not travel. If you experience emergency symptoms, seek medical help immediately. If you experience any symptoms within 10 days of testing you should restart your isolation with day 0 on the day you first experience symptoms.
  • This CDC recommendation is highly confusing and controversial. We agree with experts who say the shorter 5-day isolation should depend on being vaccinated, having a negative COVID test after 5 days, and continued use of an effective mask after the 5 days. We also agree with experts who say that a negative test should be required before someone leaves isolation prior to day 5. People at higher risk of severe COVID-19 or who live or work near others at higher risk should be especially cautious, since the 5-day limit is based on the average risk of exposures, not all exposures.
  • For people who are fully vaccinated and who were in close contact (within 6 feet for at least 15 minutes) with someone with COVID-19, the CDC now recommends (as of August 24, 2022) that you get tested 5-7 days after exposure even if you don’t have symptoms.  CDC recommends that fully vaccinated people don’t need to quarantine if they don’t have symptoms, but should wear a mask for 10 days or until their test result is negative. Quarantine refers to the time following close contact with someone known to have COVID-19 if you do not have test results confirming COVID.
  • For anyone who is exposed, the best thing to do is get tested for SARS-CoV-2 on the 5thday after exposure. If you have symptoms, immediately quarantine until a negative test result indicates you do not have the COVID-19 virus.

In general, the more people you interact with, the more closely you interact with them, and the longer that interaction, the greater your chances of becoming infected or infecting others. Things to consider:

  • How many people will you interact with?  (The fewer the better)
  • Can you keep 6 feet of space between you and others?
  • Will you be outdoors or indoors? (Outdoors is safer if it isn’t crowded. It can be heated, but not if it has walls all around and a ceiling.)
  • What’s the length of time that you will be interacting with people? (Shorter than 15 minutes is better)

The CDC recommends all individuals, both vaccinated and unvaccinated, wear a face mask or covering in indoor public transportation settings. Masking may be required in other places by local or state authorities. Research conclusively shows that face masks that cover your mouth and nose help to prevent the spread of the coronavirus. Some masks are more effective than others: stretchy “gators” may actually do more harm than good, and bandanas and scarves are too loose to be very helpful. Paper surgical masks worn in hospitals are effective and so are cloth masks you can make for yourself or buy, if they are made of cotton and at least two layers thick. Masks are important to prevent people from spreading the virus and also to help prevent infection or serious symptoms for the person wearing the masks.

Other ways to reduce your risk of contracting COVID-19 include:

  • Wash your hands using soap and water for at least 20 seconds, especially after being out in public
  • Use alcohol-based hand sanitizer when soap and water aren’t available (or wash your hands as soon as you get home)
  • Avoid touching your face when your hands aren’t clean or you are out in public
  • Put the toilet seat down before flushing in a shared or public bathroom
  • A lower priority would be to clean and disinfect surfaces including doorknobs, light switches, faucet handles, and phones. An antibacterial cleaning agent won’t kill a virus, so try to find one that is effective for killing viruses.

If you have a weakened immune system or other serious health problems, here are extra steps to protect yourself:

  • Make a plan with your doctor to monitor for symptoms
  • Have a plan with your loved ones or caregiver if you or they get sick
  • Have the medications you rely on and order any you need in advance (to be delivered, if possible)
  • Ask a friend or family member to shop for groceries for you
  • Wash your hands (20 seconds with soap and water) even more often if you are exposed to others

For healthcare workers on the frontline of the COVID-19 pandemic, a study from Cantonal Hospital St. Gallen in Switzerland reported that workers who wore a respirator mask had a 21% likelihood of infection versus those with surgical masks who had a 35% likelihood of infection. However the study did not infer causality, so there isn’t concrete evidence that respirator masking policies should be stricter, but healthcare workers at risk could benefit from wearing respirators while caring for their patients with SARS-CoV-2.

View our other articles for basic information about the virus, and what to do if you have symptoms.


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