CIDRAP - Center for Infectious Disease Research & Policy Preliminary findings of mRNA Covid-19 vaccine safety in pregnant persons. We were not able to evaluate more detailed measures of relative clinical severity in hospitalised patients (such as intensive care unit admittance), but our finding that estimated severity reductions comparing omicron with delta are larger for more severe endpoints (death and hospital admission versus hospital attendance) agrees with observations that the proportion of hospitalised COVID-19 patients requiring intensive care or mechanical ventilation (or both) has been substantially lower during the omicron wave in England than the preceding delta wave. Article 226, 236 e1236.e14 (2022). By comparison, from two to 25 weeks after the second dose, protection against Omicron hospitalization was 64%, the UKHSA said. conducted all statistical analysis in collaboration with O.Z. Google Scholar. **** ICU admission and IMV are not mutually exclusive categories, and patients could have received both. A free-text field for other types of residences was examined; patients with an LTCF-type residence were also categorized as LTCF residents. JAMA Netw. https://www.medrxiv.org/content/10.1101/2022.01.11.22269045v1, https://data.cdc.gov/Vaccinations/COVID-19-Vaccination-Demographics-in-the-United-St/km4m-vcsb. Cookies used to make website functionality more relevant to you. Christopher A. Taylor, PhD1; Michael Whitaker, MPH1; Onika Anglin, MPH1,2; Jennifer Milucky, MSPH1; Kadam Patel, MPH1,2; Huong Pham, MPH1; Shua J. Chai, MD3,4; Nisha B. Alden, MPH5; Kimberly Yousey-Hindes, MPH6; Evan J. Anderson, MD7,8,9; Kenzie Teno, MPH10; Libby Reeg, MPH11; Kathryn Como-Sabetti, MPH12; Molly Bleecker, MA13; Grant Barney, MPH14; Nancy M. Bennett, MD15; Laurie M. Billing, MPH16; Melissa Sutton, MD17; H. Keipp Talbot, MD18; Keegan McCaffrey19; Fiona P. Havers, MD1; COVID-NET Surveillance Team (View author affiliations). Age-adjusted rates were calculated by dividing the number of hospitalized COVID-19 patients by population estimates for race/ethnicity, and vaccination status in the catchment area. In conclusion, in this population-based cohort study, we found that infants born to mothers who received at least two doses of an mRNA COVID-19 vaccine during pregnancy were at lower risk of testing positive for SARS-CoV-2 and were at lower risk of hospitalization during the first 6 months of life compared with infants whose mothers were unvaccinated during pregnancy. These findings are consistent with estimates of booster effectiveness against symptomatic Omicron infection using healthcare ascertainment. The results were unchanged when no adjustments for covariates were made (Supplemental Table3). Without the vaccines many more people would likely be in hospital. 20, 15225 (2016). Marks, K. J. et al. CDC. Wkly. The company also said full results of its 2,250-person study confirmed the pill's promising early results against the virus: The drug reduced combined hospitalizations and deaths by about 89. During the Omicron-predominant period, hospitalization rates increased among unvaccinated persons and those who completed a primary series, with and without receipt of a booster or additional dose (Figure 2). IMV status was missing in 1.4% (weighted) of hospitalizations; these hospitalizations are otherwise included elsewhere in the analysis. J. The TND is designed to better control for bias related to health care-seeking behavior31,32. During the Delta period, we found that protection extended through the infants first 6 months of life. If material is not included in the articles Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. Shook, L. L. et al. In the Omicron variant period, the effectiveness of maternal vaccination in these three age intervals was 21% (CI: 21,48), 14% (CI: 9,32) and 13% (CI: 3,26), respectively. Maternal vaccination with at least two doses reduced the infants risk of testing SARS-CoV-2 positive initially by 84% which decreased to 56% by 6 months of life in the Delta dominant period. However, infants aged <6 months are not currently eligible for any currently available COVID-19 vaccines and must rely on placentally acquired immunity from their mothers. Vaccination offers the best way to protect against COVID-19 and its complications. Iowa does not provide data on vaccination status. J. TN and NMF were responsible for visualisation. Am. "The subpopulations with the highest risk should be considered a priority for COVID-19 therapeutics and further booster doses.". Author's reply, Efficacy, safety, and immunogenicity of the DNA SARS-CoV-2 vaccine (ZyCoV-D): the interim efficacy results of a phase 3, randomised, double-blind, placebo-controlled study in India, Centers for Disease Control and Prevention, MRC Biostatistics Unit COVID-19 Working Group, Cases, hospital admissions, and hospital attendances in those with delta and omicron SARS-CoV-2 variants, between Nov 29, 2021, and Jan 9, 2022, Risk of hospitalisation and mortality for COVID-19 cases with omicron compared with delta, overall and by age group, Estimated HRs for vaccination categories, secondary analysis. 1CDC COVID-19 Emergency Response Team; 2General Dynamics Information Technology, Atlanta, Georgia; 3California Emerging Infections Program, Oakland, California; 4Career Epidemiology Field Officer Program, CDC; 5Colorado Department of Public Health & Environment; 6Connecticut Emerging Infections Program, Yale School of Public Health, New Haven, Connecticut; 7Emory University School of Medicine, Atlanta, Georgia; 8Georgia Emerging Infections Program, Georgia Department of Public Health; 9Atlanta Veterans Affairs Medical Center, Atlanta, Georgia; 10Iowa Department of Public Health; 11Michigan Department of Health and Human Services; 12Minnesota Department of Health; 13New Mexico Emerging Infections Program, University of New Mexico, Albuquerque, New Mexico; 14New York State Department of Health; 15University of Rochester School of Medicine and Dentistry, Rochester, New York; 16Ohio Department of Health; 17Public Health Division, Oregon Health Authority; 18Vanderbilt University Medical Center, Nashville, Tennessee; 19Utah Department of Health. COVID-19Associated Hospitalizations Among Adults During SARS-CoV-2 Delta and Omicron Variant Predominance, by Race/Ethnicity and Vaccination Status COVID-NET, 14 States, July 2021January 2022. J. Med. Relative to the Delta-predominant period, a larger proportion of hospitalized Black adults were unvaccinated. ***** An additional 172 (3.4%, 95% CI=2.7%4.2%) adults were partially vaccinated, 69 (0.9%, 95% CI=0.61.2) received a primary vaccination series <14 days before a positive for SARS-CoV-2 test result, and 186 (4.1%) had unknown vaccination status; these groups are not further described in this analysis. Omicron data in UK is 'enormously worrying,' immunologist says "In the last two weeks, no fewer than 80% of admissions were below the age of 50 years. The aim of the secondary design was to compare the results of the cohort with TND. * Data are from a weighted sample of hospitalized nonpregnant adults with completed medical record abstractions and a discharge disposition. The views expressed are those of the authors and not necessarily those of the NIHR or the Department of Health and Social Care. Annually, approximately 40,000 births occur at KPNC facilities. Abbreviation: COVID-NET = COVID-19Associated Hospitalization Surveillance Network. Danino, D. et al. Maternal vaccination was protective, but protection was lower during Omicron than during Delta. Maryland did not contribute data after December 4, 2021, but did contribute data for previous weeks. B., Lewis. During the period of Omicron predominance, hospitalization rates increased most sharply among Black adults in the United States relative to all other racial and ethnic groups examined and reached the highest rate observed among all racial and ethnic groups since the beginning of the pandemic. After adjusting for covariates, vaccination during pregnancy significantly reduced the risk of the infant testing SARS-CoV-2 positive by 84% (95% confidence interval [CI]: 66, 93) during the first 2 months of life, 62% (95% CI: 39, 77) during the first 4 months of life and 56% (95% CI: 34,71) during the first 6 months of life. According to the CDC, hospitalization rates among the unvaccinated were 16 times higher in December overall. The average death rate among Americans over age 65 who contract the flu has ranged between 1 in 75 and 1 in 160 in recent years, according to the C.D.C. Thompson, M. G. et al. However, protection estimates greater than 90% might be too high if individuals with a previous infection were more likely than those without one to come forward for a test for reasons other than suspicion of COVID-19. In this analysis, we estimated the odds ratio (OR) of vaccination of mothers of infants who tested positive for SARS-CoV-2 versus infants who tested negative using logistic regression models conditioned (stratified) on the calendar date of the test so that infants testing positive on a certain day were compared to infants testing negative on that same day. On March 18, 2022, this report was posted online as an MMWR Early Release. During the study period, home testing became more prevalent. Google Scholar. All adults should stay up to date with COVID-19 vaccination to reduce their risk for COVID-19associated hospitalization. https://doi.org . State data show the average age for COVID deaths was about 80 in late 2020, but dropped in spring 2021 to as low as 69 after most older adults received their first COVID vaccines. To obtain From this cohort, the study excluded the following infants born to (1) mothers who were not between ages 16 and 50 years at pregnancy onset; (2) mothers who did not have a primary KPNC facility assignment; (3) mothers who were not continuous KPNC members from December 15, 2020 until delivery; (4) mothers who had a positive nasal/throat swab for SARS-CoV-2 by polymerase chain reaction (PCR) prior to pregnancy onset; (5) mothers who had a positive SARS-CoV-2 antibody test documented by KPNC prior to the onset of pregnancy; (6) mothers who received one or more doses of COVID-19 vaccine prior to pregnancy onset. Med. Pediatr. Ann Intern Med 2021;174:140919. They help us to know which pages are the most and least popular and see how visitors move around the site. Wkly. Johnson AG, Amin AB, Ali AR, et al. During the study period, the omicron variant experienced a rapidly increasing incidence, whereas the delta variant was experiencing a decreasing or less rapidly increasing incidence. COVID-19; IL-6 . Department of Health and Human Services. Safety and efficacy of the BNT162b2 mRNA covid-19 vaccine. Published by Elsevier Ltd. 1). Children and COVID-19: state data report. CDC is not responsible for Section 508 compliance (accessibility) on other federal or private website. Internet Explorer). On 13 December, Denmark released data showing that hospitalization rates for people infected with Omicron seemed to be on a par with those for people infected with other variants. The vaccines have proved highly safe and effective at reducing the risk of severe illness, hospitalization and death. BNT162b2 vaccine effectiveness against omicron in children 5 to 11 years of age. Hospitalisation associated with SARS-CoV-2 delta variant in Denmark. 383, 26032615 (2020). The funders played no direct role in the study. Our study was strengthened both by its large sample size and our ability to follow infants through 6 months of age. In all models, we used calendar days as the time scale to account for changes over time in SARS-CoV-2 circulation and vaccine uptake. and B.F. P.R. Among the infants in the cohort, 19,418 (64.06%) of the mothers were unvaccinated during pregnancy, 1138 (3.75%) of the mothers received one dose of an mRNA COVID-19 vaccine and 9755 (32.18%) received 2 doses during pregnancy (Table1). J. Med. Safety and efficacy of single-dose Ad26.COV2.S vaccine against Covid-19. Article Among nonpregnant and pregnant adults aged 18 years, hospitalization rates were calculated overall, and by race/ethnicity and COVID-19 vaccination status. 45 C.F.R. During the Omicron period, among children whose mothers received 1 dose before pregnancy and 1 dose during pregnancy, VE against infection was 46% (95% CI: 23, 77) during the first 2 months of life, 16% (95% CI: 28, 50) during the first 4 months of life and 3% (95% CI: 32, 36) during the first 6 months of life compared with children whose mothers were unvaccinated (Supplemental Table4). Klein, N. P. et al. Schrag, S. J. et al. Vaccine 35, 72977301 (2017). In this design, we used Cox proportional hazards models with calendar days as the underlying scale to estimate hazard ratios and calculated vaccine effectiveness as 1 minus the hazard ratio. Individual and neighborhood factors associated with failure to vaccinate against influenza during pregnancy. New federal data shows adults who received the updated shots cut their risk of being hospitalized with . In the meantime, to ensure continued support, we are displaying the site without styles Most mothers (66.14%) were between ages 25 and <35 years, and more than a quarter (27.27%) were of Asian race, 5.16% were Black, 24.44% were of Hispanic ethnicity and 37.57% were White. Health and Human Services. 241(d); 5 U.S.C. SARS-CoV-2 delta VOC in Scotland: demographics, risk of hospital admission, and vaccine effectiveness. 26K views, 1.2K likes, 65 loves, 454 comments, 23 shares, Facebook Watch Videos from Citizen TV Kenya: #FridayNight All authors (O.Z., B.F., N.P.K., T.R., M.G., E.L., P.R., K.G., S.O., and E.L.) critically reviewed the manuscript and decided to proceed with publication. However, data currently available on the persistence of immunity after vaccination on the one hand and the emergence of viral variants with reduced sensibility to vaccine immunity on the other, raise the need to administer boosters to maintain the protection and to compare . The study setting was Kaiser Permanente Northern California (KPNC), an integrated healthcare delivery organization that provides comprehensive healthcare to ~4.4 million members as of 2019. Racial and ethnic disparities in rates of COVID-19associated hospitalization, intensive care unit admission, and in-hospital death in the United States from March 2020 to February 2021. The efficacy of COVID 19 vaccines for reducing the risk of severe COVID-19 infection is demonstrated in real life. To ensure stability and reliability of rates by vaccination status, data are presented beginning 14 days after at least 5% of the age group-specific population of the COVID-NET surveillance catchment area has received an additional or booster dose. Protection during both periods decreased as infants aged from 2 months to 6 months. JAMA 326, 16291631 (2021). We observed a similar pattern in vaccine effectiveness by trimester during the Omicron dominant period, however, estimates of vaccine effectiveness by trimester were imprecise and much lower than during the Delta period (Table3). Dis. If SARS-CoV-2 test date was missing, hospitalization admission date was used. The final study population included 30311 (48.8%) infants who were KPNC members at least 2 months after birth. Structural changes in the brain may explain the persistent fatigue and neuropsychiatric complications tied to long COVID. However, a milder virus could still put pressure . The images or other third party material in this article are included in the articles Creative Commons license, unless indicated otherwise in a credit line to the material. Foo, D., Sarna, M., Pereira, G., Moore, H. C. & Regan, A. K. Longitudinal, population-based cohort study of prenatal influenza vaccination and influenza infection in childhood. All these results were similar to those when no adjustments for covariates are made (Supplemental Table1). Data from the COVID-19Associated Hospitalization Surveillance Network (COVID-NET) were analyzed to compare COVID-19associated hospitalization rates among adults aged 18 years during B.1.617.2 (Delta; July 1December 18, 2021) and Omicron (December 19, 2021January 31, 2022) variant predominance, overall and by race/ethnicity and vaccination status. Rep. 71, 2630 (2022). part 56; 42 U.S.C. of Omicron-infected patients with a high rate of vaccination in China. Starting the week ending December 4, 2021, Maryland data are not included in weekly rate calculations but are included in previous weeks. J. Med. As of January 26, 2022, 39.6% of Black persons received a primary vaccine series; of those, 43.9% of adults received a booster dose once eligible. We examined the effectiveness of maternal vaccination against SARS-CoV-2 infection in 30,311 infants born at Kaiser Permanente Northern California from December 15, 2020, to May 31, 2022. Atlanta, GA: US Department of Health and Human Services, CDC; 2022. We calculated VE as 100% multiplied by 1- OR. The stats are for COVID-associated hospitalizations, which may include people for whom COVID-19 was not the primary reason for admission. We conducted secondary sensitivity analyses restricting the population to infants who received at least one SARS-CoV-2 PCR test. The findings in this report are subject to at least four limitations. Dr. Klein reported receiving grants from Pfizer, Merck, GlaxoSmithKline, and Sanofi Pasteur. Gordon, N. & Lin, T. The Kaiser Permanente Northern California adult member health survey. Questions or messages regarding errors in formatting should be addressed to A previous study conducted before the Omicron-predominant period that showed increased risk for COVID-19associated hospitalization among certain racial and ethnic groups, including Black adults, and suggested the increased hospitalization rates were likely multifactorial and could include increased prevalence of underlying medical conditions, increased community-level exposure to and incidence of COVID-19, and poor access to health care in these groups (7). 139, e20164091 (2017). During Omicron predominance, children aged <6 months accounted for 44% of hospitalizations among children ages 04 years3. This analysis describes weekly hospitalization rates during Delta- and Omicron-predominant periods. Overall, the study results support recommendations for vaccination during pregnancy to protect both mothers and their infants. With the emergence of the SARS-CoV-2 Omicron variant in late 2021, Canadian public health case/contact testing was scaled back due to high infection rates with milder symptoms in a highly vaccinated population. Urban Health 83, 10411062 (2006). The cumulative monthly age-adjusted hospitalization rate during January 2022 among unvaccinated adults (528.2) was 12 times the rates among those who had received a booster or additional dose (45.0) and four times the rates among adults who received a primary series, but no booster or additional dose (133.5). KPNC members are similar to the broad catchment population in Northern California in terms of sociodemographic characteristics34. Lipkind, H. S. et al. We take your privacy seriously. Effectiveness of Two Doses of BNT162b2 Vaccine before and during Proxy Omicron Period. E.L. coordinated administrative tasks. This activity was reviewed by CDC and conducted consistent with applicable federal law and CDC policy.. In the present study, the mothers of only 32% of infants in the cohort received at least 2 doses during pregnancy. A continuity correction has been applied to the denominators by capping the percent population vaccination coverage at 95% by assuming that at least 5% of each age group would always be unvaccinated in each jurisdiction. N. Engl. As with previous variants, being vaccinated greatly protects you from severe disease with omicron. N. Engl. Delta period: July 1, 2021December 18, 2021, reflects the time when Delta was the predominant circulating variant; Omicron period: December 19, 2021January 31, 2022, reflects the time when Omicron was the predominant circulating variant. Klein, N. P. et al. N. Engl. 2022 The Authors. Aircraft wastewater surveillance could be used with traveler-based surveillance to provide an early warning system for COVID-19 and other pathogens. The rate among adults who received a primary series, but no booster or additional dose (133.5), was three times the rate among adults who received a booster or additional dose (45.0). Because the immune status of all patients is not known, an additional dose (recommended for persons with a weakened immune system) cannot be distinguished from a booster dose. Infect. Mothers were classified as either having had 2 doses or one dose of mRNA COVID-19 vaccines during pregnancy (and completed more than 14 days prior to delivery) or not having had any COVID-19 vaccines prior to delivery. Adults who received booster doses were classified as those who completed the primary series and received an additional or booster dose on or after August 13, 2021, at any time after completion of the primary series, and 14 days before a positive test result for SARS-CoV-2, as COVID-19associated hospitalizations are a lagging indicator and time passed after receipt of a booster dose has been shown to be associated with reduced rates of COVID-19 infection (https://www.nejm.org/doi/full/10.1056/NEJMoa2114255). Arthur Reingold, Jeremy Roland, Ashley Coates, California Emerging Infections Program, Oakland, California; Breanna Kawasaki, Rachel Herlihy, Isaac Armistead, Madelyn Lensing, Jordan Surgnier, Sarah McLafferty, Colorado Department of Public Health & Environment; Ann Basting, Tessa Carter, Maria Correa, Daewi Kim, Carol Lyons, Hazhia Sorosindi, Connecticut Emerging Infections Program, Yale School of Public Health, New Haven, Connecticut; Emily Fawcett, Katelyn Ward, Jana Manning, Asmith Joseph, Allison Roebling, Chandler Surell, Stephanie Lehman, Taylor Eisenstein, Suzanne Segler, Grayson Kallas, Marina Bruck, Rayna Ceaser, Annabel Patterson, Sabrina Hendrick, Johanna Hernandez, Hope Wilson, School of Medicine, Emory University, Georgia Emerging Infections Program, Georgia Department of Public Health, Veterans Affairs Medical Center, Foundation for Atlanta Veterans Education and Research, Atlanta, Georgia; Jim Collins, Shannon Johnson, Justin Henderson, Sue Kim, Alexander Kohrman, Lauren Leegwater, Val Tellez Nunez, Sierra Peguies-Khan, Michigan Department of Health and Human Services; Kayla Bilski, Kristen Ehresmann, Richard Danila, Jake Garfin, Grace Hernandez, Kieu My Phi, Ruth Lynfield, Sara Vetter, Xiong Wang, Minnesota Department of Health; Daniel M. Sosin, Susan L. Ropp, Sunshine Martinez, Jasmyn Sanchez, Cory Cline, Melissa Judson, Florent Nkouaga, Mark Montoya, New Mexico Department of Health; Sarah Lathrop, Kathy M. Angeles, Yadira Salazar-Sanchez, Sarah A. Khanlian, Nancy Eisenberg, Dominic Rudin, Sarah Shrum Davis, Mayvilynne Poblete, Emily B. Hancock, Francesca Pacheco, New Mexico Emerging Infections Program; Yassir Talha, Celina Chavez, Jennifer Akpo, Alesia Reed, Murtada Khalifa, CDC Foundation, New Mexico Department of Health; Suzanne McGuire, Kerianne Engesser, Nancy Spina, Adam Rowe, New York State Department of Health; Sophrena Bushey, Virginia Cafferky, Maria Gaitan, Christine Long, Thomas Peer, Kevin Popham, University of Rochester School of Medicine and Dentistry, Rochester, New York; Julie Freshwater, Denise Ingabire-Smith, Ann Salvator, Rebekah Sutter, Ohio Department of Health; Sam Hawkins, Public Health Division, Oregon Health Authority; Tiffanie Markus, Katie Dyer, Karen Leib, Terri McMinn, Danielle Ndi, Gail Hughett, Emmanuel Sackey, Kathy Billings, Anise Elie, Manideepthi Pemmaraju, Vanderbilt University Medical Center, Nashville, Tennessee; Amanda Carter, Andrea George, Andrew Haraghey, Ashley Swain, Caitlin Shaw, Laine McCullough, Mary Hill, Ryan Chatelain, Salt Lake County Health Department, Salt Lake City, Utah; Alvin Shultz, Robert W. Pinner, Rainy Henry, Sonja Mali Nti-Berko, CDC; Elizabeth Daly, Council of State and Territorial Epidemiologists. Morb. We did not assess whether vaccines received before pregnancy or immediately after pregnancy were associated with a reduced risk of testing positive for SARS-CoV-2 in infants. Vaccine 35, 58505857 (2017). Background: Risk stratification models have been developed to identify patients that are at a higher risk of COVID-19 infection and severe illness. It is critical that nursing home residents stay up to date with CO VID-19 vaccines and receive a bivalent booster dose to maximize protection against COVID-19. Additional COVID-NET methods for determining vaccination status have been described previously. This correction ensures that there is always a reasonable denominator for the unvaccinated population that would prevent hospitalization rates from growing unrealistically large because of potential overestimates of vaccination coverage. Weekly rates among unvaccinated adults and adults who received a primary COVID-19 vaccination series with a booster or additional dose peaked at 149.8 (January 8, 2022) and 11.7 (January 22, 2022), respectively. Rep. 70, 895899 (2021). Wkly. Pediatrics. Between December 15, 2020, and May 31, 2022, we identified 62,117 infants born at Kaiser Permanente Northern California (KPNC), an integrated healthcare delivery organization. Several conditions, including cancer of the blood or bone marrow and dementia, were associated with HRs greater than 3. By the end of December, Omicron made up 58% of all cases in the US, per Our World in Data, but Delta is thought to cause more severe disease and more hospitalizations than Omicron on average. Open 5, e2232760 (2022). Sign up for notifications from Insider! Vaccinated patients during the Delta wave were 37% (over with two doses), while during the Omicron wave they were 57%. Beginning the week of December 1925, 2021, the B.1.1.529 (Omicron) variant of SARS-CoV-2 (the virus that causes COVID-19) became the predominant circulating variant in the United States (i.e., accounted for >50% of sequenced isolates). The cohort analyses may be biased toward the null if some infected infants were misclassified as uninfected due to the absence of a SARS-CoV-2 test result in the medical record. ** Total hospitalizations include data from selected counties in 14 COVID-NET states irrespective of vaccination status and includes adults with partial or unknown vaccination status. Age was the most important risk factor for COVID-19 death (eg, HR, 31.3 for an 80-year-old vs a 50-year-old). The TND, a case-control study, has been commonly used in studies of the effectiveness of influenza vaccines and more recently COVID-19 vaccines. Rates cannot be stratified by pregnancy status because the underlying population of pregnant women in the catchment area is unknown. Association of COVID-19 vaccination during pregnancy with incidence of SARS-CoV-2 infection in infants. Three recent epidemiological studies found that vaccination during pregnancy was associated with a reduced risk of SARS-CoV-2 infection in infants during their first 4 months of life and a reduced risk of hospitalization during the first 5 months of life17,18,19. Hospitalization rates were 10.5 times higher in the unvaccinated and 2.5 times higher in vaccinated patients with no booster than in booster recipients. mmwrq@cdc.gov. You will be subject to the destination website's privacy policy when you follow the link. Cookies used to track the effectiveness of CDC public health campaigns through clickthrough data.