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Coronavirus 2019 (COVID-19)

Updated August 1, 2024

Contents

Recommendations from the Advisory Committee on Immunization Practices (ACIP)

Children & Adolescents

  • All children without contraindications 6 months to 4 years of age should receive a primary COVID-19 vaccine series comprising either:
    • 3 doses of Pfizer-BioNTech COVID-19 vaccine (trade name: Comirnaty®) administered with 3-8 weeks between doses 1 and 2 and at least 8 weeks between doses 2 and 3, and at least 1 dose of which is updated for the current (2024-2025) season;
    • 2 doses of Moderna COVID-19 vaccine (trade name: Spikevax®) administered 4-8 weeks apart, at least 1 dose of which is updated for the current (2024-2025) season.
  • Children 6 months to 4 years of age who already received a primary COVID-19 vaccine series prior to the current season should receive an additional dose updated for the current (2023-2024) season, at least 8 weeks after their last dose.
  • All children ages 5-11 without contraindications should receive an mRNA (Pfizer-BioNTech or Moderna) COVID-19 vaccine updated for the current (2024-2025) season, at least 2 months after a previous dose of COVID-19 vaccine.
  • All adolescents ages 12-17 without contraindications should receive a COVID-19 vaccine updated for the current (2024-2025) season, at least 2 months after a previous dose of COVID-19 vaccine.
  • Children and adolescents who have moderately to severely compromised immune systems may receive additional updated doses at least 2 months after a previous dose of COVID-19 vaccine.

Adults

  • All adults (age 18 or older) without contraindications should receive a COVID-19 vaccine updated for the current (2024-2025) season, at least 2 months after a previous dose of COVID-19 vaccine.
  • Adults who have moderately to severely compromised immune systems may receive additional updated doses at least 2 months after a previous dose of updated COVID-19 vaccine 1, 2.
  • Adults ages 65 and older should receive an additional dose of COVID-19 vaccine updated for the current (2024-2025) season, at least 4 months after a previous dose of updated COVID-19 vaccine 3.

For More Information

Important Information for Obstetric Providers

  • COVID-19 vaccine is recommended during pregnancy.

Disease

COVID-19 is caused by the SARS-CoV-2 virus, a type of coronavirus that began spreading in humans in 2019. SARS-CoV-2 generally enters the body through the mouth or nose via small liquid particles (ranging from larger respiratory droplets to smaller aerosols). Prevention measures other than vaccination include avoiding poorly ventilated public indoor spaces, keeping at least 6 feet of separation from others, and wearing a mask when separation from others is not feasible.

The incubation period of COVID-19 averages 5-6 days and ranges 2-14 days. Most infected persons experience mild to moderate respiratory illness and recover without medical intervention. However, some infected persons develop severe illness and require medical attention to mitigate risk of serious complications or death.

Severe illness and death occur in persons of all ages but is much more common among older adults as well as those with underlying medical conditions such as cancer, cardiovascular disease, chronic respiratory disease, or diabetes.

The most common symptoms of COVID-19 are fever, cough, fatigue, and sudden olfactory dysfunction or anosmia (loss of smell/taste). Other less, but still relatively common, symptoms include sore throat, headache, body ache, and diarrhea. Symptoms indicating a need for emergency medical attention include difficulty breathing or shortness of breath, chest pain/pressure, loss of speech/mobility or increase in confusion, or discoloration (e.g. pale, grey, blue) of skin or nail beds of fingers/toes. 4, 5

Vaccines

Four COVID-19 vaccines have been authorized in the United States: two messenger ribonucleic acid (mRNA) vaccines (Pfizer-BioNTech and Moderna), one viral vector vaccine (J&J), and one protein subunit vaccine (Novavax). As of June 2023, J&J vaccine is no longer authorized in the US 6.

Although these are the first mRNA vaccines authorized for public use, the technology behind the mRNA vaccines has been studied and developed for years. This prior work allowed mRNA vaccines specific to COVID-19 to be created very quickly once the genome of the SARS-CoV-2 virus was determined. The injected mRNA uses a person’s own cells to produce the spike protein from the virus, stimulating an antibody response that provides protection against natural infection. mRNA does not enter the nucleus of cells and is broken down quickly 7. 

The J&J vaccine is a non-replicating adenovirus type 26-vectored vaccine. Viral vector technology has been well studied and used for other vaccines such as Ebola. In viral vector vaccines, a modified virus is used as a vector to deliver a specific gene to a person’s cells that instructs the cells to produce the target protein (the COVID-19 spike protein), stimulating antibody response and protection against disease. This is not considered a live vaccine. Although the vector delivers information to human cells, the virus does not replicate 8.

The Novavax vaccine is a protein subunit vaccines. Protein subunit technology has been well studied and used for decades for other vaccines such as Hepatitis B. Protein subunit vaccines contain proteins of a virus (the COVID-19 spike protein) to induce a person’s immune cells to create antibodies specific to that protein and protect against disease. Protein subunit vaccines also contain an adjuvant to stimulate the immune response 9.

Emergency Use Authorization and Accelerated Timeline

The Food and Drug Administration (FDA) issued Emergency Use Authorization (EUA) for both mRNA COVID-19 vaccines in December 2020; first the Pfizer-BioNTech vaccine (for ages 16 and older) 10, followed by the Moderna vaccine (for ages 18 and older) 11. The FDA issued EUA for the J&J vaccine (for ages 18 and older) in February 2021 12. The FDA issued EUA for the Novavax vaccine (for ages 18 and older) in July 2022 13. The FDA revoked EUA for J&J vaccine in June 2023, per the manufacturer request, as the vaccine purchased by the government had expired and there was no demand for new vaccine 6.

The FDA expanded the EUA for the Pfizer-BioNTech vaccine to include adolescents 12-16 years of age in May 2021 14, and children at least 5 years of age in October 2021 15. The FDA then expanded the EUAs for both the Pfizer-BioNTech and Moderna vaccines to include children at least 6 months of age in June 2022 16. To better protect against circulating variants, the FDA expanded the EUAs for the Pfizer-BioNTech and Moderna vaccines to include updated bivalent formulations in August 2022 17, initially for adolescents and adults but eventually for children as well 18-20. The FDA then expanded EUAs again to include the updated monovalent formulations corresponding to the Omicron variant XBB.1.5, for the Pfizer-BioNTech and Moderna vaccines in September 2023 21, and the Novavax vaccine in October 2023 22.

The Pfizer-BioNTech vaccine (trade name: Comirnaty®) was fully approved by the FDA in August 2021 for persons at least 16 years of age 23 and in July 2022 for persons 12 to 15 years of age 24. The Moderna vaccine (trade name: Spikevax®) was fully approved by the FDA in January 2022 for persons at least 18 years of age 25.

Many factors contributed to the unprecedentedly rapid development, testing, and authorization of COVID-19 vaccine candidates. Some of these factors include combining clinical phases, rapid accumulation of assessable cases due to the high rate of disease and reduction of financial risk to manufacturers. The FDA maintains rigorous standards for vaccine efficacy and safety for both EUA and final complete approval. The risk of moving at a rapid pace for EUA has been mainly financial; if a vaccine candidate is found not to meet safety and efficacy standards at any point, it is discontinued and the money invested to conduct these trials and create the manufacturing capacity for the vaccine ahead of time is lost. This financial risk has largely been taken on by governments and manufacturers. Supporting the development of multiple vaccine candidates increases the chances that some vaccine candidates will prove to be very safe and effective and will be manufactured at scale in time to make a difference in the fight against this ongoing pandemic 26, 27.

Contraindications and Precautions

A history of immediate allergic reaction of any severity to a COVID-19 vaccine, or to any component of a COVID-19 vaccine is a contraindication to receive additional doses of the vaccine. Persons with known allergic reactions to polyethylene glycol (PEG) should not receive the mRNA vaccines. Persons who had allergic reactions that were not severe may be able to receive a COVID-19 vaccine after evaluation by an allergist-immunologist.

A history of severe allergic reaction (e.g., anaphylaxis) to any other vaccine or injectable therapy is a precaution to COVID-19 vaccination; persons with such a history may be vaccinated but should be counseled about the potential risks before and observed for 30 minutes after vaccination. Moderate or severe acute illness is also a precaution to COVID-19 vaccination; such persons should be counseled about the potential risks and observed for 15 minutes after vaccine administration.

Those with a history of mild allergic reaction to a vaccine or a history of allergic reactions (including severe allergic reactions) unrelated to vaccines, PEG, and polysorbate may proceed with COVID-19 vaccination. There are currently no other contraindications or precautions to COVID-19 vaccination including immunocompromising conditions, pregnancy, and lactation. These recommendations may change as further information becomes available and will be updated on the CDC website accordingly 27.

Vaccine Effectiveness

The Pfizer-BioNTech vaccine prevented COVID-19 with 95% efficacy (95%CI: 90.3-97.6) in its phase III clinical trial starting one week after the second dose (among participants over 16 years of age without prior evidence of natural infection). Efficacy remained at least 94% when including participants with prior infection. Efficacy was consistent across demographic subgroups. One severe case of COVID-19 occurred in the vaccine group compared to 4 in the placebo group 29. Among a subset of adolescents 12-15 years of age, the Pfizer-BioNTech vaccine produced a greater immune response than among young adults (16-25 years of age) and prevented COVID-19 with 100% efficacy 30. Among children 5-11 years of age, the Pfizer-BioNTech vaccine prevented COVID-19 with 90.7% efficacy (95%CI: 67.7%-98.3%) 31.

The Moderna vaccine prevented COVID-19 with 94.5% efficacy (95%CI: 86.5%-97.8%) in its phase III clinical trial starting two weeks after the second dose (among adults without prior evidence of natural infection). Efficacy remained at least 93% when including participants with prior infection. Efficacy was consistent across demographic subgroups. All 11 severe cases of COVID-19 occurred in the placebo group 32.

The J&J vaccine prevented moderate to severe COVID-19 with 67% efficacy (95%CI: 59.0-73.4) among adults in its phase III clinical trial starting two weeks after vaccination. Efficacy was consistent across demographic subgroups (e.g., age, comorbidity, race, ethnicity). As of February 5, 2021, 7 COVID-19 related deaths occurred in the placebo group compared to 0 in the vaccine group 33.

Real-world data support the effectiveness of vaccines against COVID-19 infection, symptoms, hospitalization, and death. In a prospective cohort of nearly 4,000 health care personnel tested weekly for 13 weeks through March 2021, full immunization (≥14 days after dose 2) was 90% effective against infection (95%CI: 68-97), and partial immunization (≥14 days after dose 1 but before dose 2) was 80% effective against infection (95%CI: 59-90), regardless of symptoms 34. In a multisite test-negative study among health care personnel through March 2021, full immunization was 94% effective against symptomatic disease, and partial immunization was 82% effective against symptomatic disease 35. In a retrospective case-control study of more than 136,000 individuals in five states between December 2020 and April 2021, at least one dose of Pfizer-BioNTech or Moderna vaccine was 86% and 93% effective against infection, respectively, and both vaccines were 100% effective in preventing COVID-19-associated intensive care unit (ICU) admission 36. The effectiveness of J&J vaccine against COVID-19 infection and hospitalization was lower than the effectiveness of either mRNA vaccine, though still impactful 37.

The effectiveness of COVID-19 vaccines against infection slowly declines over time and are also somewhat less effective against infection with some newer variants (such as Delta and Omicron) compared to the original strain. However, COVID-19 vaccines still greatly reduce the risk of infection and remain highly effective at preventing severe disease and death 38, 39, provided persons stay up to date with recommended booster doses 40.

Vaccine Safety

Common side effects from Pfizer-BioNTech vaccine among participants in its phase III clinical trial over 16 years of age included: injection site reactions (e.g., pain, redness, swelling) (84%), fatigue (63%), headache (55%), muscle pain (38%), chills (32%), joint pain (24%), and fever (14%). The vast majority of these were mild to moderate, resolving within a couple of days after onset. Systemic effects were more common and severe after the second dose compared to the first, with the most frequent “severe” side effects of the second dose being fatigue (5%), headache (3%), chills (2%), and muscle pain (2%). Most of these effects were less common and milder among older adults compared to younger adults. Among adverse events of special interest (AESIs) which could possibly be related to vaccination, lymphadenopathy (axillary swelling and tenderness of the vaccination arm) was reported in 64 vaccine recipients (0.3%) compared to only 6 (<0.1%) in the placebo group, lasting 10 days on average. Facial nerve palsy was reported in four vaccine recipients (<0.1%) and none in placebo recipients. The observed rate is consistent with the expected background rate in the general population, and there was no time clustering to suggest a causal relationship. No other notable patterns that would suggest a causal relationship were noted by the FDA. This includes deaths, of which 2 were reported among vaccine recipients and 4 among placebo recipients, numbers consistent with the expected background rate in the general population for these age groups 29. Rates of common side effects among adolescents 12-15 years of age were similar to rates among young adults (16-25 years of age), and no vaccine-related serious adverse events occurred among adolescents 12-15 years of age 30. Among children 5-11 years of age, some injection site reactions (e.g., redness, swelling) were higher than among young adults, but rates of systemic reactions (e.g., fever) were lower than among young adults, reactogenicity was mostly mild to moderate and quickly resolving, and no vaccine-related serious adverse events occurred 31, 41, 42.

Common side effects from Moderna vaccine in its phase III clinical trial included: injection site pain (92%), fatigue (69%), headache (63%), muscle pain (60%), joint pain (45%), chills (43%), and fever (15%). The vast majority of these were mild to moderate. Systemic effects were more common and severe after the second dose compared to the first, with the most frequent “severe” side effects of the second dose being fatigue (10%), headache (6%), muscle pain (9%), joint pain (5%), and chills (1%). However, most of these effects were less common and milder among older adults compared to younger adults. Among adverse events of special interest (AESIs) which could possibly be related to vaccination, lymphadenopathy was reported in 173 vaccine recipients (1.1%) compared to 95 (0.6%) in the placebo group. Facial nerve palsy was reported by three vaccine recipients and one placebo recipient; the low frequency was consistent with the expected background rate in the general population. Hypersensitivity wase reported in 1.5% of vaccine recipients compared to 1.1% of placebo recipients; however, no episodes of anaphylaxis or severe hypersensitivity had close temporal relation to the vaccine. Three vaccine recipients with dermal fillers reported swelling at the site of the fillers after vaccination; two of these were reported as serious adverse events (SAEs), but all resolved over time. No other notable patterns that would suggest a causal relationship were noted by the FDA. This includes deaths, of which 6 were reported among vaccine recipients and 7 among placebo recipients, numbers consistent with the expected background rate in the general population for these age groups 32.

Common side effects from J&J vaccine in its phase III clinical trial included: injection site pain (49%), headache (39%), fatigue (38%), muscle pain (33%), nausea (14%), and fever (9%). The vast majority of these were mild to moderate, resolving within a couple of days after onset. Adverse events with numerical imbalances between groups included: urticaria (hives), which was reported in 5 vaccine recipients compared to 1 in the placebo group; thromboembolic events, which were reported in 15 vaccine recipients compared to 10 in the placebo group; and tinnitus, which was reported in 6 vaccine recipients compared to none in the placebo group. These data are insufficient to determine causality. No other notable patterns that would suggest a causal relationship were noted by the FDA. This includes deaths; 5 were reported among vaccine recipients and 20 among placebo recipients as of February 5, 2021 33.

Rarely, allergic reactions occur after COVID-19 vaccination due to hypersensitivity to a vaccine component such as polyethelene glycol (PEG) 43. PEG can be found in osmotic laxatives and oral bowel preparations for colonoscopy procedures, among other medications. Cross-reactive hypersensitivity between PEG and polysorbates may also occur. Polysorbates can be found in many licensed vaccines, as well as some injectable drugs (e.g., corticosteroids), biological agents and monoclonal antibodies. Higher than expected rates of anaphylaxis following the Pfizer-BioNTech (~4.7 cases per million doses) and Moderna (~2.5 cases per million doses) COVID-19 vaccines have been identified 44, as compared to ~1 case per million doses for most other vaccines 45. The CDC provides guidance for screening to detect individuals who might be at risk, managing allergic reactions, and recommendations for those who experience an allergic reaction after receiving a COVID-19 vaccine or have a history of allergic reactions. Personnel at all sites administering these (and other) vaccines should be prepared to promptly treat individuals who develop allergic reactions. All vaccine recipients should be observed for at least 15 minutes after vaccination to safeguard against potential allergic reactions; persons with a history of anaphylaxis should be observed for at least 30 minutes 46. See the Contraindications and Precautions section above as well as the Do Vaccines Cause Hypersensitivity Reactions? summary for more details.

mRNA COVID-19 vaccines have been shown to rarely cause myocarditis, most frequently among adolescent males after their second dose. Estimates of incidence vary by study but have mostly ranged between about 1 case per 2,500 to 1 case per 10,000 among males aged 12-17 after their second dose. Estimates of incidence are lower after the first and booster doses, among males of other age groups, and among females. Estimates of incidence are also higher after SARS-CoV-2 infection than after vaccination 47-52. The risk of myocarditis seems to be about twice as high for Spikevax (Moderna) compared to Comirnaty (Pfizer) vaccines 49, 50, 53, 54. However, it is difficult to make direct comparisons and combine data between studies on this topic, due to variability in the populations and vaccines studied, the methods used for case ascertainment and study design, how associations are reported, and study limitations. In particular, much of the available data are not adequately stratified by age and sex. An increased risk of pericarditis has also been shown after second and booster doses of mRNA COVID-19 vaccines, though less common than myocarditis and more evenly distributed between sexes and age groups 51, 55. See the Do Vaccines Cause Myocarditis Or Myocardopathy/Cardiomyopathy? summary for more details.

J&J vaccination has been associated with very rare cases of thrombosis with thrombocytopenia syndrome (TTS). TTS is a serious condition involving blood clots with low platelets and has mostly occurred in women 30-49 years of age. The FDA and CDC paused J&J vaccination on April 13, 2021 after 6 cases of TTS were reported to the US passive safety monitoring system Vaccine Adverse Event Reporting System (VAERS) so that these cases could be investigated further. The pause was ultimately lifted on April 23, 2021, by which time the total cases reported to VAERS had grown to 15, as the ACIP determined that the benefits of vaccination outweighed the risks due to the rarity of TTS and the risks of COVID-19 56, 57. J&J vaccination may have also been associated with very rare cases of Guillain-Barré Syndrome (GBS). Data from the VSD, as of November 13, 2021, estimated an unadjusted incidence rate of 34.6 confirmed cases of GBS per 100,000 person-years within 21 days after J&J vaccination (95%CI: 15.8-65.7), significantly higher than the background rate, and an adjusted risk ratio (versus 22-42 days after vaccination) of 6.03 (95% CI: 0.79-147.79) 58. As of December 16, 2021, 54 cases of TTS (37 in females and 17 in males) and 8 TTS-related deaths had been confirmed following J&J vaccination (out of 14.1 million doses administered), and the ACIP recommended preferential use of mRNA COVID-19 vaccines over J&J vaccine 59. The FDA revoked EUA for J&J vaccine in June 20236.

Other rare adverse events identified in an evaluation of data from over 2.4 million persons receiving the Pfizer-BioNTech vaccine in Israel included lymphadenopathy (with an excess risk of 78.4 events per 100,000 persons), herpes zoster (with an excess risk of 15.8 events per 100,000 persons), and appendicitis (with an excess risk of 5.0 events per 100,000 persons) 60. See the Do Vaccines Cause Herpes Zoster? summary for more details.

COVID-19 vaccines cannot cause COVID-19 infection or disease as the SARS-CoV-2 virus is not contained in the vaccines. COVID-19 vaccines also cannot affect DNA 7,8.

Considerations in Pregnancy

Pregnant individuals should be vaccinated against COVID-19.

Initially, only limited data on vaccine efficacy and safety were available among pregnant and breastfeeding individuals, as they were excluded from clinical trials. The manufacturers conducted Developmental and Reproductive Toxicity (DART) studies in animals and identified no safety signals 61.

Early data on the efficacy of mRNA COVID-19 vaccines during pregnancy are promising. Immune responses among pregnant individuals appear similar to non-pregnant individuals, and vaccine-generated antibodies transferred to unborn infants via the umbilical cord and recently born infants via breastmilk 62. Effectiveness of the Pfizer-BioNTech vaccine among pregnant individuals appears high and comparable to the general population 63, 64.

Early data on the safety of mRNA COVID-19 vaccines during pregnancy are reassuring; no obvious signals have arisen in safety monitoring for pregnant individuals or their babies 65, and active case-control surveillance found no link between vaccination and spontaneous abortion 66.

The available COVID-19 vaccines are not live vaccines and the theoretical risks are minimal. COVID-19 vaccines help protect pregnant individuals and their unborn children from COVID-19. Thus, the American College of Obstetricians and Gynecologists (ACOG) has recommended that all pregnant and lactating individuals be vaccinated against COVID-19 67. Pregnancy registries have been established to monitor the outcomes of women pregnant at the time of vaccination 68, 69.

Fundamentals for Discussion

  1. Specific Concerns

  2. Disease Risk

    • As your doctor, I know that you want to make the best choices about vaccines for you and your family.
    • I also know there is a lot of information out there, and it is difficult to figure out who to trust.
    • Would it be okay if I share with you what I have learned from my experience, and what I share with my patients, my family and my friends about COVID-19?
  3. Vaccine Effectiveness
    • The good news about COVID-19 is that there are effective vaccines. mRNA COVID-19 vaccines are over 90% efficacious.

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