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Detailed Breakdown of ABRYSVO - Pfizer's New RSV Vaccine
This is a detailed breakdown of the studies referenced in the article covering Pfizer’s new RSV vaccine - ABRYSVO. You can click on any of the titles below to be taken directly to that studies breakdown. Once you’re at the study’s breakdown, there’s a link available in blue under the title to take you to the original published study. Enjoy!
Bivalent Prefusion F Vaccine in Pregnancy to
Prevent RSV Illness in Infants
Key Points
a. 3682 pregnant mothers received the vaccine and 3676 mother received placebo.
b. At 180 days (approx. 6 months) 57 infants from mothers who received the vaccine had contracted an RSV infection, and 117 infants from mothers who had received placebo had contracted an RSV infection
c. Absolute risk of contracting RSV for vaccinated group was 1.55% compared to 3.19% for placebo group.
Calculating Number Needed to Harm (NNH) and Number Needed to Vaccinate (NNV)
For these calculations, I used the data provided in their Supplementary appendix. According to Pfizer, there were 7126 infants (3568 in vaccinated group and 3558 in placebo group) that were followed during their first month of life. Among those in the vaccinated group, 2016 adverse events were reported in the first month. Among those in the placebo group, 1929 adverse events were reported. When we do the math, this means that the NNH is 43.73. In other words, for about every 44th mother who receives a vaccine, there’s a chance that one infant may experience and adverse event in the 1st month of life.
The investigators also reported on serious adverse events in the two groups over the course of the first 24 months of life. Here they stated that 794 of the infants within the vaccine group experienced a serious adverse event while 768 of the infants in the placebo group experienced a serious adverse event over the course of 24 months. Using these values, the NNH would actually be approximately 149.65. So, that means that based on this data, if 150 mothers received the Pfizer vaccine, there’s a chance that one infant may experience a serious adverse event that could be caused by the vaccine.
As a quick reminder, these NNH’s don’t tell us whether or not the vaccine is safe. And on their own they’re kind of just there. They’re most useful when we can put them alongside the number needed to treat/vaccinate (NNV). The NNV is a calculation of how many patients needed to be vaccinated in order for one patient to receive the benefit of vaccination. And again, this is an estimation.
For the Pfizer vaccine, we can use two separate instances to determine NNV. We can look at the NNV for general RSV infection and we can calculate NNV to prevent severe cases of RSV. Pfizer reported 57 cases of RSV in the first 180 days among infants whose mothers had received the vaccine. They reported 117 cases in the placebo group. Using these number, we can calculate the NNV to be 61.17. This means that we would need to vaccinate approximately 61 mothers in order to hopefully prevent one RSV case in infants within the first 180 days of life.
For severe cases, Pfizer reported 19 cases in the first 180 days among infants whose mothers had received the vaccine. They reported 62 cases in the placebo group. This would make the NNV to prevent severe cases of RSV approximately 85.43. These means that 85 to 86 mothers would need to receive the vaccine in order to hopefully prevent one single case of severe RSV infection in an infant that is younger than 180 days.
Putting these side by side, here’s what we find. The NNH in the first month of life is 43.73. The NNV to prevent any case of RSV in the first 180 days is 61.17 and to prevent severe infection is 85.43.
The NNH and potentially cause a serious adverse event in the first 24 months of life is 149.65. Again, this in comparison to the NNV of 61.17 to prevent an RSV infection in the first 180 days and 85.43 to prevent severe infection.
Medically Attended Illness due to Respiratory Syncytial Virus Infection Among Infants Born in the United States Between 2016 and 2020
Key Points:
a. Three data sources were reviewed for their analysis
b. Data was from 1 April 2016 to 29 February 2020
c. Reported on rate of outpatient, emergency department (ED), and hospitalization rates
d. Included rate for children who born at term and generally healthy, children who would qualify for preemptive RSV antibody use, and children born with other risk factors
i. Children born at term and generally health
1)Outpatient treatment: ranged from 2.34 - 2.8%
2)ED treatment: ranged from .72 - 1.9%
3)Hospitalized for treatment: ranged from .696 - 956%
ii. Children who would qualify for preemptive RSV antibody use
1)Outpatient treatment: ranged from .067 - .115%
2)ED treatment: ranged from .025 - .061%
3)Hospitalized for treatment: ranged from .064 - .10%
iii. Children with other risk factors
1)Outpatient treatment: ranged from .424 - .573%
2)ED treatment: ranged from .176 - .369%
3)Hospitalized for treatment: ranged from .252 - .366%
Incidence of Respiratory Syncytial Virus Lower Respiratory Tract Infections During the First 2 Years of Life: A Prospective Study Across Diverse Global Settings
Key Points
a. Observational study with 2401 participants across 8 countries, 329 were in the US.
b. Participants were followed from birth to 2 years of age
c. No hospitalizations due to RSV were found in US cohort
d. Approximately 2% of US participants experienced their fist bout with RSV during the two years
Respiratory Syncytial Virus Burden and Healthcare Utilization in United States Infants <1 Year of Age: Study of Nationally Representative Databases, 2011-2019
Key Points
a. Estimated average rate of ED visits and hospitalizations due to RSV
b. Used data from Nationally Representative Databases from 2011 to 2019
i. Average rate of ED visits annually: 4.74%
ii. Average rate of RSV Hospitalization in 2019: 1.72%
Mortality Associated With Respiratory Syncytial Virus, Bronchiolitis, and Influenza Among Infants in the United States: A Birth Cohort Study From 1999 to 2018
Key Points
a. Calculated mortality rate of RSV in children younger than 12 months old using data from 1999 to 2018
b. Reported 561 infant deaths associated with RSV in those 20 years
c. Calculated average annual number of RSV deaths was 28 for a calculated mortality rate of .00062%
Respiratory Syncytial Virus-Associated Hospitalization Rates among US Infants: A Systematic Review and Meta-Analysis
Key Points
a. 25 studies were reviewed and analyzed
b. Looked specifically at hospitalization rates reported from four different types of studies : Active surveillance, Retrospective Medical Record Review (MRR), ICD-9 Codes, and Model Based
i. Active surveillance: Median rate of hospitalization – 1.112%
ii. Retrospective MRR: Median rate of hospitalization – .98%
iii. ICD-9 Code: Median rate of hospitalization – 2.20%
iv. Model Based: Median rate of hospitalization – 2.37%
References
1. Kampmann B, Madhi SA, Munjal I, Simões EAF,et al; MATISSE Study Group. Bivalent Prefusion F Vaccine in Pregnancy to Prevent RSV Illness in Infants. N Engl J Med. 2023 Apr 20;388(16):1451-1464. doi: 10.1056/NEJMoa2216480. Epub 2023 Apr 5. PMID: 37018474.
2. US FDA. FDA Approves First Vaccine for Pregnant Individuals to Prevent RSV in Infants. FDA News Release. 2023 Aug 21. Accessed on 2024 Feb 4 at https://www.fda.gov/news-events/press-announcements/fda-approves-first-vaccine-pregnant-individuals-prevent-rsv-infants
3. Gantenberg JR, van Aalst R, Zimmerman N, et al. Medically Attended Illness due to Respiratory Syncytial Virus Infection Among Infants Born in the United States Between 2016 and 2020. J Infect Dis. 2022 Aug 15;226(Suppl 2):S164-S174. doi: 10.1093/infdis/jiac185. PMID: 35968869; PMCID: PMC9377038.
4. Langley JM, Bianco V, Domachowske JB, et al. Incidence of Respiratory Syncytial Virus Lower Respiratory Tract Infections During the First 2 Years of Life: A Prospective Study Across Diverse Global Settings. J Infect Dis. 2022 Aug 26;226(3):374-385. doi: 10.1093/infdis/jiac227. PMID: 35668702; PMCID: PMC9417131.
5. Suh M, Movva N, Jiang X, Reichert H, et al. Respiratory Syncytial Virus Burden and Healthcare Utilization in United States Infants <1 Year of Age: Study of Nationally Representative Databases, 2011-2019. J Infect Dis. 2022 Aug 15;226(Suppl 2):S184-S194. doi: 10.1093/infdis/jiac155. PMID: 35968879; PMCID: PMC9377028.
6. Reichert H, Suh M, Jiang X, et al. Mortality Associated With Respiratory Syncytial Virus, Bronchiolitis, and Influenza Among Infants in the United States: A Birth Cohort Study From 1999 to 2018. J Infect Dis. 2022 Aug 15;226(Suppl 2):S246-S254. doi: 10.1093/infdis/jiac127. PMID: 35968877; PMCID: PMC9377030.
7. McLaughlin JM, Khan F, Schmitt HJ, et al. Respiratory Syncytial Virus-Associated Hospitalization Rates among US Infants: A Systematic Review and Meta-Analysis. J Infect Dis. 2022 Mar 15;225(6):1100-1111. doi: 10.1093/infdis/jiaa752. PMID: 33346360; PMCID: PMC8921994.