Public health officials in the United States have recommended influenza vaccination for pregnant people since 1960, but the first recommendation by the Advisory Committee on Immunization Practices (ACIP) for influenza vaccine administration during pregnancy was made in 1997. ¹ Three other vaccines, including those to prevent tetanus-diphtheria-acellular pertussis (Tdap) in 2011,² coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in 2021,³ and respiratory syncytial virus (RSV) in 2023,⁴ have since been recommended for pregnant people. Several vaccines, including human papillomavirus (HPV) vaccine and live viral vaccines like varicella, are not recommended during pregnancy.⁵ Hepatitis B, hepatitis A, and travel vaccines may be administered if the pregnant person is at risk.⁵ The Vaccine Safety Datalink (VSD),⁶ a collaboration between 13 healthcare organizations and the Centers for Disease Control and Prevention (CDC), monitors vaccination, including during pregnancy, to assess coverage and safety and to inform public health officials about the uptake of these vaccines.

The VSD uses two validated algorithms to identify ongoing and completed pregnancies, including those ending in non-live births (e.g., spontaneous abortion, stillbirth).⁷ The algorithms estimate gestational age, pregnancy start date, and end date using data from electronic health records (EHR), insurance claims, linked birth certificates, and administrative databases. For this analysis, we identified completed pregnancies (i.e., those that ended in live births, non-live births, or terminations) that started January 1, 2002 through December 31, 2022 among people 12 through 55 years of age. Eight VSD sites contributed data to this analysis: Denver Health [CO], HealthPartners [MN], Marshfield Clinic [WI], and the Colorado, Northern California, Northwest [OR/WA], Southern California, and Washington Kaiser Permanente regions. Two of these sites were not able to contribute data for the full study period.

To describe the uptake of vaccination during pregnancy, we identified all vaccines received during the pregnancies in the study period, excluding those received on the pregnancy end date. Vaccination data were extracted from EHR, insurance claims, and linked regional and state immunization information systems (IIS).⁸ We excluded vaccine records that were implausible based on calendar date and product availability (e.g., COVID-19 vaccine administered in 2012), experimental vaccines, and non-vaccine products, such as immunoglobulins. We described vaccines received by trimester (1^st trimester=less than 14 weeks’ gestation, 2^nd trimester=14 through less than 28 weeks’ gestation, 3^rd trimester=28 weeks’ gestation through the pregnancy end date) based on the gestational age estimated by the algorithms. We also calculated the average number of vaccines administered during pregnancy annually by dividing the number of vaccines administered during pregnancy by the number of pregnancies that started in each calendar year. This study was approved by the institutional review boards of all participating sites with a waiver of informed consent because this was a minimal risk observational study and was conducted consistent with federal law and CDC policy (see 45 C.F.R. part 46.114; 21 C.F.R. part 56.114).

Over the study period, we identified 2,943,789 completed pregnancies among people 12 through 55 years of age, and 2,472,612 vaccinations during those pregnancies (Table). The average number of pregnancies identified each year was 140,180 and ranged from 104,434 (2003) to 163,026 (2021). We excluded 175 vaccine records with implausible dates (172 novel pandemic monovalent H1N1 influenza, 2 COVID-19, 1 HPV), and 153 records of non-vaccine products administered during pregnancy. The average number of vaccinations per pregnancy increased from 0.07 in 2002 to 1.35 in 2022, with larger increases noted in 2009, 2013, 2014, and 2021. The average number peaked in 2021 at 1.86 when the primary COVID-19 series was widely available in the United States.

Inactivated seasonal influenza (1,122,749 doses) and Tdap (1,067,739 doses) vaccines accounted for 89% of all vaccinations received during pregnancy during the study period (Table). From 2020 through 2022, 164,043 doses of COVID-19 vaccines were administered during pregnancy. In 2009 and 2010, 48,610 doses of pandemic monovalent H1N1 influenza vaccine were administered. Other vaccines administered included: hepatitis B (23,100 doses), HPV (9,991 doses), tetanus-diphtheria (Td) (8,701 doses), hepatitis A (4,876 doses), pneumococcal (4,744 doses), and measles-mumps-rubella (MMR) (3,082 doses). An additional 13,162 vaccine doses were categorized as “other”. Included in this “other” category were live viral vaccines contraindicated during pregnancy: 2,247 doses of varicella vaccine, 1,824 doses of live attenuated influenza vaccine (LAIV), 29 doses of zoster vaccine, and 18 doses of smallpox (vaccinia) vaccine (data not shown).

The timing of vaccination during pregnancy varied by vaccine (Table). Consistent with ACIP recommendations, influenza and COVID-19 vaccinations occurred across trimesters, and 82% of Tdap vaccines were given during the 3^rd trimester. For vaccines contraindicated or not recommended during pregnancy, 91% of HPV, 86% of smallpox, 73% of varicella, 72% of LAIV, 60% of MMR, and 59% of zoster vaccinations occurred in the 1^st trimester (data not shown for smallpox, varicella, LAIV, and zoster vaccines).

From 2002 through 2022, increases in the number of vaccinations administered per pregnancy were observed in the VSD, particularly following the introduction of pandemic vaccines (H1N1 influenza in 2009 and COVID-19 in 2020), and the 2013 updated recommendation for Tdap vaccination during every pregnancy.⁹ These observed increases do not represent increased vaccination coverage during pregnancy, but instead reflect the increasing number of vaccines approved or recommended for use during pregnancy. Seasonal influenza and Tdap vaccines accounted for 89% of all vaccinations administered during pregnancy.

Four vaccines are currently recommended during pregnancy in the United States,⁵ and additional vaccines may soon be licensed and recommended for use during pregnancy. The VSD will continue to monitor vaccination trends and safety during pregnancy and is well-positioned to provide timely estimates of vaccine uptake during pandemics or after new products are licensed and recommended.

VSD data presented here suggest that the timing of inactivated influenza, Tdap, and COVID-19 vaccine administration is largely consistent with ACIP recommendations for pregnant people. Some vaccines that are not recommended or are contraindicated for pregnant people, such as HPV and varicella, are also being administered during pregnancy, but the pattern of primarily 1^st trimester administration suggests that these vaccines may be received before the patient and/or provider are aware of the pregnancy.

This study is subject to several possible limitations. First, pregnant people included in the VSD are usually insured and receive health care during pregnancy; therefore, the vaccination patterns observed in this population may not be generalizable to those who are uninsured and/or not receiving care. While the populations included in the VSD are generally representative of the underlying communities at each VSD site,¹⁰ results may not be generalizable to other geographic regions of the United States that might have higher or lower rates of vaccination. Second, although the pregnancy algorithms have been shown to have high rates of agreement with medical record review, some misclassification of pregnancy start and end dates is possible.⁷ Third, vaccine records and administration dates may also be impacted by misclassification, although we excluded vaccines that were implausible based on administration dates and product availability. Fourth, VSD includes several sources of vaccine data, including EHR, insurance claims, and linked IIS, but it is possible that vaccines administered outside of participating healthcare systems were not captured, which would result in underestimates of vaccine uptake. Finally, because our study period ended with the 2022 calendar year, we did not describe uptake of the recently recommended RSV vaccine in this study. However, the VSD is monitoring RSV vaccine uptake and data are publicly available on the CDC’s RSVVaxView webpage (https://www.cdc.gov/vaccines/imz-managers/coverage/rsvvaxview/). Additionally, the VSD publishes detailed weekly seasonal influenza and COVID-19 coverage data on the CDC’s FluVaxView webpage (https://www.cdc.gov/flu/fluvaxview/) and COVIDVaxView webpage (https://www.cdc.gov/vaccines/imz-managers/coverage/covidvaxview/), respectively.

The VSD provides timely information about real-world implementation of vaccination recommendations for pregnant people, including uptake of vaccines during pandemics. These data can also highlight adherence to vaccination recommendations and can be used to monitor administration of vaccines that are not recommended or are contraindicated during pregnancy.