They could be less healthy than the wider population. A method is introduced for computing a Bayesian 95 per cent posterior probability region for vaccine efficacy. More than 22 million people have now received the first dose of the Covid-19 vaccine in the UK. Neonatal outcomes after antenatal influenza immunization during the 2009 H1N1 influenza pandemic: impact on preterm birth, birth weight, and small for gestational age birth. Infectious disease specialist Dr. Sumon Chakrabarti explains what the different efficacy rates for the COVID-19 vaccines mean. Pediatr Infect Dis J 2007;26:619–28. The final results, however, do indicate a slightly lower vaccine efficacy of 86% among volunteers aged 65 and older, although the difference may be the result of the smaller number of COVID-19 cases reported. H1N1 influenza vaccination during pregnancy and fetal and neonatal outcomes. Despite the universal importance of vaccines, approaches to human and veterinary vaccine evaluation differ markedly. An RCT of children aged 6–24 months reported vaccine efficacy of 66% against laboratory-confirmed influenza in 1999-2000 but no vaccine efficacy during the second year when there was little influenza activity[19]. How do we measure how well influenza vaccines work? It is not possible to predict how well the vaccine and circulating strains will be matched in advance of the influenza season, nor is it possible to predict how this match may affect vaccine effectiveness. Such trials may exclude children, or those who with compromised immune systems. How well does the live attenuated influenza vaccine (LAIV) work compared to inactivated influenza vaccine (IIV)? The test-negative study design minimizes selection bias related to health care seeking by enrolling patients who seek care for a respiratory illness. An observational study in the United States during 2010-11 and 2011-12 using a test-negative design reported vaccine effectiveness of 44% (95% CI: 5 to 67) against influenza among pregnant woman[28]. Even before the second dose, BNT162b2 was highly efficacious, with a vaccine efficacy of 92.6%, a finding similar to the first-dose efficacy of 92.1% reported for the mRNA-1273 vaccine … Since the match between circulating and vaccine viruses is not known before the season, annual estimates of vaccine effectiveness give a real-world look at how well the vaccine protects against influenza caused by circulating viruses each season. Several RCTs have been done in healthy adults aged <65 years[7,8,9,10,11,12]. studies on their pharmaceutical quality and studies to check first the effects in laboratory tests and animals).. Then vaccines are tested in human volunteers in studies called clinical trials.These tests help confirm how the vaccines work and, importantly, to evaluate their safety and protective efficacy. This is not a survival ratio. The efficacy of the vaccine after the first dose is about 52 percent, according to Dr. William C. Gruber, senior vice president of Pfizer Vaccine Clinical Research and Development. It is typically estimated based on a marginal, or population-based, parameter, which is an average of the individual vaccine effects, specific to a geographically and temporally defined population ( Halloran et al . No effect of maternal immunization on infant birth weight was reported in the South African trial described above. This is at the 95% confidence level. 2014;371:635-45. The formulae and calculations can get quite complicated, so I will only give a simple example here. Formula where PCV = proportion of the cases vaccinated and PPV is as defined above b. What is the evidence that influenza vaccines work? For growth to be linear and not exponential, we need the average number of new infections to be one. The latter number is an estimated proportion of infected people who do not die. For example, chronic medical conditions can confound the association between influenza vaccination and hospitalization with influenza in observational studies. Comparative efficacy of inactivated and live attenuated influenza vaccines. Safety, efficacy, and effectiveness of cold-adapted influenza vaccine-trivalent against community-acquired, culture-confirmed influenza in young children attending day care. Therefore, it is important that bias be minimized with the study design or adjusted for in the analysis. In a RCT, vaccine allocation is usually double-blinded, which means neither the study volunteers nor the researchers know if a given person has received vaccine or placebo. Clin Infect Dis 2014; 58(4): 449-57. However, a randomized, school-based study in Canada reported lower rates of confirmed influenza among students vaccinated with live-attenuated vaccine compared to students vaccinated with inactivated influenza vaccine, as well as decreased influenza transmission among family members of students vaccinated with live-attenuated influenza vaccines[42]. A third candidate vaccine being developed by Johnson & Johnson may require only one shot. Efficacy and effectiveness of influenza vaccines: a systematic review and meta-analysis. Even before the second dose, BNT162b2 was highly efficacious, with a vaccine efficacy of 92.6%, a finding similar to the first-dose efficacy of 92.1% reported for the mRNA-1273 vaccine … The AstraZeneca vaccine was praised for its cost-effectiveness and its easy-to-store advantages. Many factors affect the real-world effectiveness of vaccines. Technically the FDA has requested a vaccine with 50 percent efficacy, with a margin ranging from as low as 30 percent to as high as 70 percent. Procedure—An equation was coded into a computer spreadsheet to compare the traditional sample size calculation with that needed when evaluating the effi- cacy of a vaccine applied in a population. Observational studies of influenza vaccine effectiveness can be subject to three forms of bias: confounding, selection bias, and information bias. Several observational studies have reported significant vaccine effectiveness against RT-PCR confirmed influenza-related hospitalization among older adults. Lancet 2011; 377(9767): 751-9. In addition, even when some circulating influenza viruses are significantly drifted, it is possible for other influenza viruses in circulation to be well matched to the vaccine. Vaccine effectiveness is defined as the percentage reduction in the incidence of disease among vaccinated persons compared with unvaccinated persons, as given in the following equation: Attack rates can be substituted for incidence, but in either case, some form of population denominators are needed to calculate vaccine effectiveness. DiazGranados CA, Dunning AJ, Kimmel M, Kirby D, Treanor J, Collins A, Pollak R, Christoff J, Earl J, Landolfi V, Martin E, Gurunathan S, Nathan R, Greenberg DP, Tornieporth NG, Decker MD, Talbot HK. Vaccine for prevention of mild and moderate-to-severe influenza in children. This is a simplified calculation. In a four-year RCT of inactivated vaccines among children aged 1–15 years, vaccine efficacy was estimated at 77% against influenza A (H3N2) and 91% against influenza A (H1N1) virus infection[18]. The ratio of vaccinated to unvaccinated persons (i.e., the odds of influenza vaccination) is then compared for patients with and without laboratory-confirmed influenza. Not adjusting for confounders could bias the vaccine effectiveness estimate away from the true estimate. That is 100,000 infected people — of which 1,000 die. Effect of influenza vaccination of children on infection rates in Hutterite communities: a randomized trial. Fell DB, Sprague AE, Liu N, et al. Lancet ID 2011(12): 36-44, Neuzil KM, Dupont WD, Wright PF, Edwards KM. For human vaccines, vaccine efficacy is the proportion of vaccinated individuals protected by the vaccine against a defined outcome under ideal conditions, whereas for veterinary vaccines the term is used for a range of measures of vaccine protection. For Pfizer's vaccine, the two doses are given 3 to 6 weeks apart. Talbot HK, Griffin MR, Chen Q, Zhu Y, Williams JV, Edwards, KM. Some observational studies in developed and developing countries have found lower risk of prematurity or low birth weight in babies born to vaccinated mothers, but the effect has not been consistently demonstrated[31,32,33,34,35]. Observational studies are subject to various forms of bias (see above for definition) more so than RCT studies. Pediatrics 2006;118:2298–312. Influenza viruses are continuously changing through a natural process known as antigenic drift. BMC Infect Dis 2010; 10: 71. Selection bias occurs when people with the outcome being measured by the study (i.e., influenza infection) differ from people who do not have the outcome. N Engl J Med 1998;338:1405–12. In addition, RCTs of cell-based inactivated influenza vaccines (IIVs) and recombinant trivalent HA protein vaccines have been performed among healthy adults. Darvishian M, Bijlsma MJ, Hak E, van den Heuvel ER. Two recent studies found that a pair of widely-used vaccines, which are administered through two shots given on different days, display vaccine efficacy even … Madhi SA, Cutland CL, Kuwanda L, et al. For example, a BBC headline on 16th November was: Moderna: Covid vaccine shows nearly 95% protection. Clin Infect Dis 2013;56:1216-22. This method assumes independent vague gamma prior distributions for the incidence rates on each arm of the trial, and a Poisson likelihood for the counts of incident cases of infection. In the example given, the vaccine effectiveness estimate could be biased lower, or towards lower effectiveness. Comparison of the efficacy and safety of live attenuated cold-adapted influenza vaccine, trivalent, with trivalent inactivated influenza virus vaccine in children and adolescents with asthma. (See below for details.). 1994;272(21):1661-5, Osterholm MT, Kelley NS, Sommer A, et al. Zaman K, Roy E, Arifeen SE, et al. Estimates are reported annually, and often, an early estimate is reported during the season. A randomized trial in Bangladesh found that babies born to mothers vaccinated during pregnancy with trivalent inactivated influenza vaccines were significantly less likely to be born small for gestational age and weighed an average of 200g more than babies born to unvaccinated mothers[29,30]. Those include individual factors, such as age. Observational studies assess how influenza vaccines work by comparing the occurrence of influenza among people who have been vaccinated compared to people not vaccinated. The former number is vaccine efficacy. Pediatr Infect Dis J. This is another way of phrasing vaccine efficacy. We can calculate the approximate confidence interval for vaccine efficacy. Clin Infect Dis 2010; 51(9): 997-1004. CDC twenty four seven. The new analyses estimate that the vaccine has an efficacy rate of 74 percent against asymptomatic infections. In my experience I find this pretty accurate, but even though math cannot duplicate reality, if well-managed it can produce a reasonable facsimile. Prevention of symptomatic seasonal influenza in 2005-2006 by inactivated and live attenuated vaccines. N Engl J Med 2008; 359(15): 1555-64. This rate varies by country, and may improve over the course of the pandemic. A randomised control trial might exclude some people from volunteering. Observational studies can suffer from statistical biases. On Monday, AstraZeneca released interim analysis of its phase 3 trial data of 23,000 volunteers from the U.K. and Brazil. Efficacy of high-dose versus standard-dose influenza vaccine in older adults. It is the latest vaccine candidate based on a new technology known as messenger RNA. Maternal influenza immunization and reduced likelihood of prematurity and small for gestational age births: a retrospective cohort study. That finding will … N Engl J Med 2013; 369(26): 2481-91. Sanofi and Translate Bio said on Friday they had started a human trial of their mRNA COVID-19 vaccine candidate, the French drugmaker's second vaccine project, which follows a protein-based shot hit by a delay last year. Notice that the numerator of this formula is the absolute difference in the rates R R R = 1 − 0 1 The test-negative design removes selection bias due to health-care seeking behaviors. Vaccine efficacy is: the relative change in having a disease in the vaccinated group. Chung JR, Flannery B, Thompson MG, Gaglani M, Jackson ML, MontoAS, NowalkMP, Talbot HK, Treanor JJ, Belongia EA, Murthy K, Jackson LA, G. Petrie J, Zimmerman RK, Griffin MR, McLean HQ, Fry AM. For the Moderna vaccines, the two doses are given 4 to 6 weeks apart. In addition to the test-negative design, there are additional observational study designs that have been used to estimate vaccine effectiveness. But that calculation was based on … Vaccine effectiveness is the percent reduction in the frequency of influenza illness among vaccinated people compared to people not vaccinated, usually with adjustment for factors (like presence of chronic medical conditions) that are related to both … Thompson MG, Li DK, Shifflett P, et al. Saving Lives, Protecting People. The prevalence of lingering symptoms and complications is under study, A Modest Proposal for Tracking the Covid-19 Vaccine, Pfizer’s Promising mRNA Vaccine Is Welcome News for the Country, How to Keep a Fall Surge From Becoming a Winter Catastrophe, COVID Combat Fatigue: ‘I Would Come Home With Tears in My Eyes’, Spain speaks: voices from inside the lockdown, A Second Coronavirus Death Surge Is Coming. Denmark and Norway now have serious concerns. Procedure: An equation was coded into a computer spreadsheet to compare the traditional sample size calculation with that needed when evaluating the efficacy of a vaccine applied in a population. The trial included 30,420 participants randomized to receive two … BMC Infect Dis 2009; 9. There were 170 COVID-19 cases. How well do influenza vaccines work during seasons in which the flu vaccine is not well matched to circulating influenza viruses? This article uses a differential equation to model the evolution of a pandemic such as the Coronavirus. Efficacy of inactivated split-virus influenza vaccine against culture-confirmed influenza in healthy adults: a prospective, randomized, placebo-controlled trial. The vaccine works by breaking that key. This is the reverse of the infection fatality rate. Treanor JJ, El Sahly H, King J, et al. This is an example of confounding by indication because those at greatest risk for the outcome being measured (i.e., influenza associated hospitalization) are targeted for vaccination, and therefore, they are more likely than those without a chronic medical condition to receive a flu vaccine. Two general types of studies are used to determine how well influenza vaccines work: randomized controlled trials and observational studies. We can work through an example: the Pfizer & BioNTech phase III study. Vaccine efficacy is the change in having a disease amongst those vaccinated. Also, observational studies often are the only option to measure vaccine effectiveness against more severe, less common influenza outcomes, such as hospitalization. Pediatr Infect Dis J. A little algebraic manipulation shows us that V = 5 satisfies this equation. The pharmaceutical boss behind the Oxford vaccine says researchers have found a “winning formula” to improve the jab’s efficacy. How the flu virus can change: Drift and Shift, Bridges CB, Thompson WW, Meltzer MI, Reeve GR, Talamonti WJ, Cox NJ, Lilac HA, Hall H, Klimov A, Fukuda K. Effectiveness and cost-benefit of influenza vaccination of healthy working adults: A randomized controlled trial. Efficacy of inactivated and cold-adapted vaccines against influenza A infection, 1985 to 1990: the pediatric experience. Clinical trials during 2004-05, 2005-06, and 2007-08 that compared inactivated influenza vaccines and live attenuated influenza vaccines to no vaccine among adults suggested that inactivated influenza vaccines provided better protection against influenza than live attenuated influenza vaccines in adults7,8. Efficacy and safety of 1 and 2 doses of live attenuated influenza vaccine in vaccine-naive children. Barrett PN, Berezuk G, Fritsch S, et al. Therefore, serologic testing methods can result in biased VE estimates that inflate VE. PLoS medicine 2011;8:e1000441. Beran J, Wertzova V, Honegr K, et al. A case is a person having the disease, or virus. [13] A meta-analysis that included data from RCTs of licensed inactivated influenza vaccines reported a pooled vaccine effectiveness of 59% (95% CI 51-67) against influenza confirmed by RT-PCR or viral culture[14]. As a result, even when circulating influenza viruses are mildly or moderately drifted in comparison to the vaccine, it is still possible that people may receive some protective benefit from influenza vaccination. A meta-analysis of observational studies that used the test-negative design provided VE estimates for adults aged >60 years against RT-PCR confirmed influenza infection. 2001;20(8):733-40, Hoberman A, Greenberg DP, Paradise JL, Rockette HE, Lave JR, Kearney DH, Colborn DK, Kurs-Lasky M, Haralam MA, Byers CJ, Zoffel LM, Fabian IA, Bernard BS, Kerr JD. Vaccine efficacy is measured by comparing the frequency of influenza illness in the vaccinated and the unvaccinated (placebo) groups. These studies have reported vaccine efficacy estimates ranging from 16%-75%; VE of 16% was reported during a season with few influenza infections. When the vaccine enters the body, the immune system recognizes the mRNA in it as foreign and begins producing … It also shows how to calculate approximate uncertainty around those central estimates. JAMA. The efficacy of the vaccine after the first dose is about 52 percent, according to Dr. William C. Gruber, senior vice president of Pfizer Vaccine Clinical Research and Development. For example, one group receives the vaccine; the other receives a placebo. JAMA. Vaccine efficacy refers to vaccine protection measured in RCTs usually under optimal conditions where vaccine storage and delivery are monitored and participants are usually healthy. These trials produce estimates — true efficacy could be somewhat higher or lower. Belshe RB, Gruber WC, Mendelman PM, et al. In a RCT, volunteers are assigned randomly to receive an influenza vaccine or a placebo (e.g., a shot of saline). Influenza vaccination of pregnant women and protection of their infants. In addition to virus factors, host factors such as age, underlying medical conditions, history of prior infections and prior vaccinations can affect the benefits received from vaccination. However, it is unknown if infections were missed by serology among the study participants that were vaccinated (and if the vaccine efficacy estimate is biased upwards – see previous description of how bias can occur in VE studies that test for influenza using serology). Effectiveness of seasonal trivalent influenza vaccine for preventing influenza virus illness among pregnant women: a population-based case-control study during the 2010-2011 and 2011-2012 influenza seasons. Effectiveness of maternal influenza immunization in mothers and infants. J Infect Dis 2009; 200(12): 1861-9. An efficacy of 0% means that the vaccine does not work (identical to … Monto AS, Ohmit SE, Petrie JG, et al. This article looks at what statements about ‘95% protection’ and similar claims mean. For both RCTs and observational studies, the specificity of the outcome measured in the study is important. In the test-negative design, people who seek care for an acute respiratory illness are enrolled at ambulatory care settings (such as outpatient clinics, urgent care clinics, and emergency department) and information is collected about the patients’ influenza vaccination status. Ohmit SE, Victor JC, Teich ER, et al. But still a lot find out. Although less effective than the reported results from the Pfizer or Moderna COVID-19 vaccine candidates, this vaccine is still more effective than annual influenza vaccines … Also, the characteristics of the vaccine itself — cost, storage, delivery — matter. Vaccine efficacy refers to vaccine protection measured in RCTs usually under optimal conditions where vaccine storage and delivery are monitored and participants are usually healthy. Peer-reviewed findings from the COVE trial showed the Moderna mRNA-1273 vaccine to have 94.1% efficacy for preventing Covid-19, with efficacy of 86.4% reported in older (≥65 years) study participants. J Infect Dis 2008; 198(3): 312-7. Overall, this trial provided confidence in the vaccine's efficacy and robustly documented its safety. The virus spreads, infecting 10% in the non-vaccinated population. This is a novel virus, so much still unknown about long-term effects. There are many factors which affect how effective a vaccine is. During 2010-11, the vaccine efficacy of a quadrivalent inactivated vaccine among children aged 3-8 years was 59% (95% CI: 45%-70%)[20]. Vaccine 2011; 29(44): 7733-9. Oxford vaccine says researchers have found a “winning formula” to improve the jab’s efficacy.. 2007;356(7):685-96, Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD), Reconstruction of the 1918 Influenza Pandemic Virus, 2019-2020 Preliminary In-Season Burden Estimate, Who is at High Risk for Flu Complications, Who Should & Who Should NOT Get Vaccinated, Live Attenuated Influenza Vaccine (LAIV)/Nasal Spray Vaccine, Selecting Viruses for the Seasonal Influenza Vaccine, Flu Vaccine and People with Egg Allergies, Frequently Asked Questions on Vaccine Supply, Historical Reference of Vaccine Doses Distributed, Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN), How Vaccine Effectiveness and Efficacy are Measured, What People with a Staph Infection Should Know about Flu, Resources for Hosting a Vaccination Clinic, Overview of Influenza Surveillance in the United States, Influenza Hospitalization Surveillance Network (FluSurv-NET), Weekly U.S. News reports shared trial findings of different vaccinations against COVID-19. These figures are not comparable. For all its simplicity, the Vaccine Efficacy equation has guided the development of modern vaccination and has saved millions of lives. In the Pfizer trial, the most common severe side effects were fatigue and headaches. CMAJ : Canadian Medical Association journal = journal de l’Association medicale canadienne 2012. Jackson LA, Gaglani MJ, Keyserling HL, et al. The Pfizer/BioNTech vaccine reports 90% efficacy, which means that their vaccine prevented COVID-19 symptoms for 90% of volunteers that received the vaccine compared to placebo. This is not true of observational studies. Procedure—An equation was coded into a computer … Oxford vaccine says researchers have found a “winning formula” to improve the jab’s efficacy.. N Engl J Med 2014; 371(10): 918-31. In addition, a cluster-randomized trial conducted in Hutterite communities in Canada found that vaccinating children aged 3 to 15 years with trivalent inactivated influenza vaccine before the 2008-09 season reduced RT-PCR confirmed influenza in the entire community by 61% (95% CI: 8-83), including a 59% reduction (95% CI: 5-82) in confirmed influenza among non-vaccinated community members, evidence of the “indirect” effect of influenza vaccination on prevention on disease transmission[21]. You will be subject to the destination website's privacy policy when you follow the link. An RCT in South Africa among HIV infected adults reported vaccine efficacy of 76% (95 CI 9-96). So even when circulating influenza viruses are mildly or moderately drifted in comparison to the vaccine, it is possible that people may still receive some protective benefit from vaccination; and if other circulating influenza viruses are well matched, the vaccine could still provide protective benefits overall. It is important to remember there is uncertainty around estimates. New influenza infections could be missed in a vaccinated person since antibodies are already high and a four-fold increase doesn’t develop. For example, people who visit their health care provider in outpatient settings (e.g., clinics and urgent care) are more likely to be vaccinated than people who do not go to a provider for care. Non-specific outcomes, such as pneumonia hospitalizations or influenza-like illness (ILI) can be associated with influenza virus infections as well as infections with other viruses and bacteria. Vaccination against H1N1 influenza with Pandemrix((R)) during pregnancy and delivery outcome: a Swedish register study. Blood-stage vaccine assessment. In the vaccinated population, only 10,000 people get the disease. For Canada, Finding a Vaccine Will Only Be Part of the Equation While researchers across Canada are among the scientists working on coronavirus vaccines… Surviving COVID-19 may mean suffering from long-term health conditions. For example, if researchers obtain information on vaccination for children with influenza from immunization records but ask parents of children without influenza if the child was vaccinated, this difference in data collection procedures could bias the results of the study. Safety, efficacy, and immunogenicity of an inactivated influenza vaccine in healthy adults: a randomized, placebo-controlled trial over two influenza seasons. In our situation, the approximate intervals may be too wide — or too conservative. The Pfizer/BioNTech Covid-19 vaccine being rolled out across the US should be safe for just about anyone -- even the frailest elderly people. Lancet Infect Dis 2014; 14(12): 1228-39. Vaccine efficacy (VE) is defined as the per cent reduction in the probability or hazard of disease conferred by the vaccine to an individual. Calculate the vaccine effectiveness from the varicella data in Table 3.13. Am J Public Health 2012;102:e33-40. The protective benefits of influenza vaccination are generally lower during flu seasons where the majority of circulating influenza viruses differ from the influenza viruses used to make the vaccines. In addition, the trial showed that vaccination reduced the incidence of laboratory-confirmed influenza among infants born to HIV-negative women by 49%; the study was unable to assess vaccine efficacy among infants of HIV infected women. A three-year study (2006-07 through 2008-09) in Tennessee that used a test-negative design reported vaccine effectiveness of 61% (95% CI: 18-83) among hospitalized adults >50 years of age[5]. A randomized double-blind placebo-controlled trial. The Covid-19 vaccine developed by the British drugs group AstraZeneca and the University of Oxford has achieved a "winning formula" for efficacy, the company's chief executive said on Sunday. However, as stated above, these studies cannot be conducted when vaccination is recommended in a population and these studies are very difficult to conduct for more severe outcomes that are less common. The Centers for Disease Control and Prevention (CDC) cannot attest to the accuracy of a non-federal website. Keep reading to find out more about the vaccine's efficacy, and for more on the vaccine, You Won't Be Able to Get the Pfizer COVID Vaccine in These 2 Places. Challenge of conducting a placebo-controlled randomized efficacy study for influenza vaccine in a season with low attack rate and a mismatched vaccine B strain: a concrete example. Can you describe biases that are important to consider for observational studies measuring vaccine effectiveness? This is where trial volunteers are in groups. Protective efficacy of a trivalent recombinant hemagglutinin protein vaccine (FluBlok(R)) against influenza in healthy adults: a randomized, placebo-controlled trial. “Even before the second dose, BNT162b2 was highly efficacious, with a vaccine efficacy of 92.6%, a finding similar to the first-dose efficacy of 92.1% reported for the mRNA-1273 vaccine … In this study, there were “over 43,000” participants. Serologic assays to detect influenza infection (i.e., which require a four-fold rise in antibody titers against influenza viruses detected from paired sera) were often used in past flu VE studies to detect influenza infections prior to more accurate tests, such as RT-PCR, becoming more widely available. Gaglani M , Pruszynski J, Murthy K, Clipper L, Robertson A, Reis M, Chung JR, Piedra PA, Avadhanula V, Nowalk MP Zimmerman RK, Jackson ML, Jackson LA, Petrie JG, Ohmit SE, Monto AS, McLean HQ, Belongia EA, Fry AM, Flannery B. (For more information, see How the flu virus can change: Drift and Shift.) In observational studies of influenza vaccine effectiveness, people with and without influenza may have different likelihoods of being vaccinated, and this can bias the estimate of vaccine effectiveness. Kwong J, Pereira J, Quach S, Pellizzari R, Dusome E, Russell M, et al. Effectiveness of inactivated influenza vaccine in preventing acute otitis media in young children: a randomized controlled trial. Influenza vaccine prevents medically attended influenza-associated acute respiratory illness in adults aged ≥50 years. Let’s say the R 0 for COVID-19 is 2.5, meaning each infected person infects, on average, two and a half other people (a common estimate). Therefore, the presence of a chronic medical condition in a study participant is a potential confounding factor that should be considered in analysis. Vaccine efficacy is 1 minus the relative risk, shown here times by 100. Vaccine effectiveness (VE) a. N Engl J Med 2009; 361(13): 1260-7. The reduction from 0.75% to 0.04% is then 95%. Of those, 100 die. Vaccine programmes may give at-risk groups the vaccine first. One RCT of adults aged 60 years and older relied on serology for confirmation of influenza and reported a vaccine efficacy of 58% (95% confidence interval (CI): 26-77)[2]. Effectiveness of seasonal influenza vaccine in community-dwelling elderly people: a meta-analysis of test-negative design case-control studies. These people split into two even groups. An RCT that compared a high-dose, inactivated influenza vaccine (containing four times the standard amount of influenza antigen) to standard dose vaccine in persons aged 65 years or older during the 2011-12 and 2012-13 influenza seasons found that rates of laboratory-confirmed influenza were 24% lower (95% CI: 10-37) among persons who received high-dose vaccine compared to standard dose influenza vaccine, indicating that high-dose vaccine provided 24% better protection against influenza than standard dose vaccine in this trial.[4].
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