Read and report vaccine reactions, harassment and failures.
To learn the history of the original monovalent COVID-19 vaccines developed for visit NVIC’s What is the history of COVID-19 vaccines in America webpage.
At this time effectiveness of the 2023-2024 COVID-19 vaccine containing the SARS-CoV-2 Omicron XBB.1.5 variant is unknown, as effectiveness is based on real-world data of how the vaccine works in the general population and this vaccine has just been recently approved and authorized for use in the general population.
The vaccine efficacy for the 2023-2024 monovalent COVID-19 vaccine containing the SARS-CoV-2 Omicron variant XBB.1.5 is also unknown as clinical trial were not done prior to their approval for use. Approval and authorization of these vaccines were based on clinical trial data from the original COVID-19 vaccine, as well as bivalent COVID-19 vaccines that were never approved or authorized for use.
Vaccine efficacy is based on ideal situations like well-designed clinical trials. Notably, vaccine efficacy can differ from vaccine effectiveness because a vaccine may not work as well in the real world.
Understanding what efficacy and effectiveness mean is also important. Below is an example from Yale Medicine.
“An example: Imagine there were 100 people in the vaccine group, and 100 people in the placebo group. If 10 people in the placebo group became infected, but only 2 in the vaccine group got sick, that means the vaccine has reduced the chances of illness by 80%; thus, it is considered to have an efficacy of 80%.”
A study pending peer review that was conducted by the Cleveland Clinic in early 2023 found that during the time when Omicron variant XBB was the most dominant circulating strain, individuals who were up to date with the recommended COVID-19 vaccine doses (original 2-dose series, booster, and bivalent booster) were more likely to become infected with SARS-CoV-2 than those who were not. A study published in September 2023 from COVID-19 illness rate data across 33 California prisons also noted that between January and July 2023, inmates who received the updated bivalent booster dose were more likely to contract COVID-19 illness than those who were not vaccinated.
A research letter published by the Journal of the American Medical Association in September 2023 that looked at 177,000 emergency room (ER), urgent care (UC), and outpatient visits from July 2022 through May 2023 for infants and children 6 months through 4 years of age found that two doses of the Pfizer-BioNTech COVID-19 vaccine was associated with a decreased risk of ER and UC visits, but that three doses of the vaccine had no protective effect. No data was provided on the effectiveness of a single dose of the vaccine. Of note, three doses of Pfizer-BioNTech COVID-19 vaccine is the recommended primary series for all children aged 6 months through 4 years. The third dose was added after the initial clinical trials had begun when researchers discovered that two doses of the vaccine was not effective in this population.
Multiple studies have found that vaccine effectiveness wanes quickly and vaccinated persons may be more at risk of infection.
COVID-19 Vaccine Effectiveness Data from the CDC – September 2023
Data provided from the U.S. Centers for Disease Control and Prevention (CDC) in September 2023 also reports a rapid waning of protection from the vaccine.
The CDC also notes that vaccine effectiveness data is impacted by the rates of underlying infection acquired immunity in the population and that vaccine effectiveness “findings should be interpreted as the incremental benefit provided by COVID-19 vaccination in a population with high prevalence of infection-induced immunity.”
Vaccine Effectiveness against ER/Urgent Care Visits (6 months through 5 years)
From data collected between July 2022 and August 2023, by two months following completion of the original 2 dose Moderna COVID-19 vaccine series, the vaccine was reported to be 24 percent effective in infants and young children against ER or urgent care visits. Similarly, from data collected between July 2022 and July 2023, by two months following completion of the original 3 dose Pfizer-BioNTech vaccine series, the vaccine was reported to be 16 percent in infants and young children.
CDC health officials report that a booster dose of the bivalent COVID-19 vaccine in this population given between December 2022 and June 2023 was 61 percent effective at protecting infants and young children against ER and urgent care visits. Data, however, is limited because few children received booster doses of the bivalent vaccine and vaccine effectiveness over time was not made available.
Vaccine Effectiveness in Immunocompetent Children (5 through 17 years)
From data collected between September 2022 and August 2023, three doses of the original monovalent COVID-19 vaccine were reported to be 7 percent effective against ER and Urgent Care visits in children and adolescents. A booster dose of the bivalent COVID-19 vaccine increased the vaccine effectiveness to 63 percent within the first 2 months, however, by 60 through 119 days post vaccination, the effectiveness had decreased to 36 percent.
Vaccine Effectiveness in Immunocompetent Adults (18 through 64 years)
Between September 2022 and August 2023, three doses of the original monovalent COVID-19 vaccine were reported to be 2 percent effective against ER and Urgent Care visits in adults aged 18 through 64 years. A booster dose of the bivalent COVID-19 vaccine increased the vaccine effectiveness to 56 percent within the first 2 months, but by 60 through 119 days, the vaccine’s effectiveness had decreased to 39 percent.
Three doses of the original monovalent COVID-19 vaccine in adults were reported to be 15 percent effective against hospitalization. A booster dose of the bivalent COVID-19 vaccine in immunocompetent adults was reported to increase the effectiveness to 61 percent within the first two months, but by four months, a bivalent booster dose in this population actually increased a person’s chance of hospitalization from COVID-19.
Vaccine Effectiveness in Immunocompetent Older Adults (65+ years)
From data collected between September 2022 and August 2023, three doses of the original monovalent COVID-19 vaccine were reported to be 17 percent effective against ER and Urgent Care visits in immunocompetent older adults. A booster dose of the bivalent COVID-19 vaccine increased the vaccine effectiveness to 59 percent within the first 2 months, however, by 60 through 119 days post vaccination, the effectiveness had decreased to 47 percent.
Three doses of the original monovalent COVID-19 vaccine in older adults were reported to be 25 percent effective against hospitalization. A booster dose of the bivalent COVID-19 vaccine in immunocompetent adults was reported to increase effectiveness to 67 percent within the first two months, but by four months, the effectiveness of this booster dose decreased to 28 percent.
Vaccine Effectiveness in Immunocompromised Adults (18+ years)
Three doses of the original monovalent COVID-19 vaccine in immunocompromised adults were reported to be 1 percent effective against hospitalization and critical illness. A booster dose of the bivalent COVID-19 vaccine in this population was reported to increase vaccine effectiveness to 31 percent within the first two months, but by four months, the effectiveness of this booster dose decreased to 12 percent.
There is evidence that COVID-19 vaccination can increase a person’s risk of COVID-19 illness immediately following vaccination. A pre-print study posted in February 2021 that examined Israeli vaccination data reported that COVID-19 infection rates strongly increased following vaccination, nearly doubling, until eight days post vaccination.
A published study that examined data from Public Health England found that within the first nine days following vaccination, an individual was 48 percent more likely to test positive for COVID-19 than unvaccinated individuals. Higher rates of COVID-19 were also noted in the first 13 days post vaccination among individuals who received the COVID-19 vaccine in Qatar.
An article published on September 30, 2021 in the European Journal of Epidemiology reported that vaccination has had no impact on COVID-19 rates. According to the published data that looked at COVID-19 cases in 68 countries and 2947 U.S. counties reported:
At the country-level, there appears to be no discernable relationship between percentage of population fully vaccinated and new COVID-19 cases in the last 7 days. In fact, the trend line suggests a marginally positive association such that countries with higher percentage of population fully vaccinated have higher COVID-19 cases per 1 million people.
Study authors recommended that strategies focusing on vaccination as a primary method of mitigating COVID-19 be re-evaluated.
A pre-print study pending peer review conducted primarily by Danish researchers and published in April 2022 found that mRNA COVID-19 vaccines have had no impact on reducing all-cause mortality in randomized controlled trials (RCTs). Scientists involved in the research found that mRNA COVID-19 vaccines were only protective against fatal infection, while adenovirus vaccines such as the Janssen/Johnson & Johnson vaccine "were associated with lower overall mortality and lower non-accident, non-COVID-19 mortality." The paper also found that while mRNA COVID-19 vaccines reduced COVID-19 deaths, the vaccine increased cardiovascular deaths, but that the data for either was not statistically significant.
An analysis conducted for The Health 202 in the fall of 2022 reported a higher mortality rate in COVID-19 vaccinated individuals than those who were unvaccinated. According to the study, in August 2022, 58 percent of deaths occurred in individuals who were either vaccinated or vaccinated and boosted. This was an increase from earlier in the year, when an estimated 42 percent of deaths occurred among vaccinated people.34
IMPORTANT NOTE: NVIC encourages you to become fully informed about covid-19 and the covid-19 vaccine by reading all sections in the Table of Contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.