The U.S Centers for Disease Control and Prevention (CDC) recommends the<unk>  vaccine as the best way to protect people against the<unk>  and prevent its spread. The<unk>  vaccine can also reduce the severity of the<unk>  if a person contracts a strain that the vaccine did not contain. It takes about two weeks following vaccination for protective antibodies to form. A 2012 meta-analysis found that<unk>  vaccination was effective 67percent of the time; the populations that benefited the most were HIV-positive adults aged 18 to 55 (76percent), healthy adults aged 18 to 46 (approximately 70percent), and healthy children aged six months to 24 months (66percent). The<unk>  also appears to protect against myocardial infarction with a benefit of 15 to 45%. Effectiveness US vaccine effectiveness by start year: 2004 10% 2005 21% 2006 52% 2007 37% 2008 41% 2009 56% 2010 60% 2011 47% 2012 49% 2013 52% 2014 19% 2015 48% 2016 40% 2017 38% 2018 29% 2019 39% 2020 N/A 2021 16% A vaccine is assessed by its efficacy – the extent to which it reduces risk of disease under controlled conditions – and its effectiveness – the observed reduction in risk after the vaccine is put into use. In the case of<unk> , effectiveness is expected to be lower than the efficacy because it is measured using the rates of<unk> -like illness, which is not always caused by<unk> .<unk> s generally show high efficacy, as measured by the antibody production in animal models or vaccinated people. However, studies on the effectiveness of<unk>  vaccines in the real world are difficult; vaccines may be imperfectly matched, virus prevalence varies widely between years, and<unk>  is often confused with other<unk> -like illnesses. However, in most years (16 of the 19 years before 2007), the<unk>  vaccine strains have been a good match for the circulating strains, and even a mismatched vaccine can often provide cross-protection. The virus rapidly changes due to antigenic drift, a slight mutation in the virus that causes a new strain to arise. Repeated annual<unk> tion generally offer consistent year-on-year protection against<unk> . There is, however, suggestive evidence that repeated vaccinations may cause a reduction in vaccine effectiveness for certain<unk>  subtypes; this has no relevance to current recommendations for yearly vaccinations but might influence future vaccination policy. , the CDC recommends a yearly vaccine as most studies demonstrate overall effectiveness of annual<unk> tion. COVID-19<unk> tion does not prevent COVID-19, but it does protect against getting<unk>  and COVID-19 at the same time, a combination which greatly increases the risk of serious illness. Research demonstrates patients infected with the two viruses are over twice as likely to die as patients with only COVID-19. Patients who have recovered from COVID-19 can safely receive an<unk> . An<unk>  and a COVID-19 vaccine may be given safely at the same time. Criticism Tom Jefferson, who has led Cochrane Collaboration reviews of<unk>  vaccines, has called clinical evidence concerning<unk>  vaccines "rubbish" and has therefore declared them to be ineffective; he has called for placebo-controlled randomized clinical trials, which most in the field hold as unethical. His views on the efficacy of<unk>  vaccines are rejected by medical institutions including the CDC and the National Institutes of Health, and by key figures in the field like Anthony Fauci. Michael Osterholm, who led the Center for Infectious Disease Research and Policy 2012 review on<unk>  vaccines, recommended getting the vaccine but criticized its promotion, saying, "We have overpromoted and overhyped this vaccine... it does not protect as promoted. It's all a sales job: it's all public relations." Children In April 2002, the Advisory Committee on Immunization Practices (ACIP) encouraged that children 6 to 23 months of age be vaccinated annually against<unk> . In 2010, ACIP recommended annual<unk> tion for those 6 months of age and older. Currently the CDC recommends that everyone except infants under the age of six months should receive the seasonal<unk> . Vaccination campaigns usually focus special attention on people who are at high risk of serious complications if they catch the<unk> , such as pregnant women, children under 59 months, the elderly, and people with chronic illnesses or weakened immune systems, as well as those to whom they are exposed, such as health care workers. As the death rate is also high among infants who catch<unk> , the CDC and the WHO recommend that household contacts and caregivers of infants be vaccinated to reduce the risk of passing an<unk>  infection to the infant. In children, the vaccine appears to decrease the risk of<unk>  and possibly<unk> -like illness. In children under the age of two data are limited. During the 2017–18<unk>  season, the CDC director indicated that 85 percent of the children who died "likely will not have been vaccinated". In the United States, , the CDC recommend that children aged six through 35 months may receive either 0.25milliliters or 0.5milliliters per dose of<unk> zone Quadrivalent. There is no preference for one or the other dose volume of<unk> zone Quadrivalent for that age group. All persons 36 months of age and older should receive 0.5 milliliters per dose of<unk> zone Quadrivalent. , Afluria Quadrivalent is licensed for children six months of age and older in the United States. Children six months through 35 months of age should receive 0.25milliliters for each dose of Afluria Quadrivalent. All persons 36 months of age and older should receive 0.5milliliters per dose of Afluria Quadrivalent. , Afluria Tetra is licensed for adults and children five years of age and older in Canada. In 2014, the Canadian National Advisory Committee on Immunization (NACI) published a review of<unk> tion in healthy 5–18-year-olds, and in 2015, published a review of the use of pediatric<unk> ad in children 6–72 months of age. In one study, conducted in a tertiary referral center, the rate of<unk> tion in children was only 31%. Higher rates were found among immuno-suppressed pediatric patients (46%), and in patients with inflammatory bowel disease (50%). Adults A US Navy hospital corpsman administers a<unk>  shot aboard the in 2020. In unvaccinated adults, 16% get symptoms similar to the<unk> , while about 10% of vaccinated adults do. Vaccination decreased confirmed cases of<unk>  from about 2.4% to 1.1%. No effect on hospitalization was found. In working adults, a review by the Cochrane Collaboration found that vaccination resulted in a modest decrease in both<unk>  symptoms and working days lost, without affecting transmission or<unk> -related complications. In healthy working adults,<unk> s can provide moderate protection against virologically confirmed<unk> , though such protection is greatly reduced or absent in some seasons. In health care workers, a 2006 review found a net benefit. Of the eighteen studies in this review, only two also assessed the relationship of patient mortality relative to staff<unk>  uptake; both found that higher rates of health care worker vaccination correlated with reduced patient deaths. A 2014 review found benefits to patients when health care workers were immunized, as supported by moderate evidence based in part on the observed reduction in all-cause deaths in patients whose health care workers were given immunization compared with comparison patients where the workers were not offered vaccine. Elderly Evidence for an effect in adults over 65 is unclear. Systematic reviews examining both randomized controlled and case–control studies found a lack of high-quality evidence. Reviews of case–control studies found effects against laboratory-confirmed<unk> , pneumonia, and death among the community-dwelling elderly. The group most vulnerable to non-pandemic<unk> , the elderly, benefits least from the vaccine. There are multiple reasons behind this steep decline in vaccine efficacy, the most common of which are the declining immunological function and frailty associated with advanced age. In a non-pandemic year, a person in the United States aged 50–64 is nearly ten times more likely to die an<unk> -associated death than a younger person, and a person over 65 is more than ten times more likely to die an<unk> -associated death than the 50–64 age group. There is a high-dose<unk>  vaccine specifically formulated to provide a stronger immune response. Available evidence indicates that vaccinating the elderly with the high-dose vaccine leads to a stronger immune response against<unk>  than the regular-dose vaccine. A<unk>  vaccine containing an adjuvant was approved by the US Food and Drug Administration (FDA) in November 2015, for use by adults aged 65 years of age and older. The vaccine is marketed as<unk> ad in the US and was first available in the 2016–2017<unk>  season. The vaccine contains the MF59C.1 adjuvant which is an oil-in-water emulsion of squalene oil. It is the first adjuvanted seasonal<unk>  vaccine marketed in the United States. It is not clear if there is a significant benefit for the elderly to use a<unk>  vaccine containing the MF59C.1 adjuvant. Per Advisory Committee on Immunization Practices guidelines,<unk> ad can be used as an alternative to other<unk> s approved for people 65 years and older. Vaccinating health
Influenza vaccine
Typhus vaccine
Measles vaccine
Polio vaccine
Hantavirus vaccine
MMR vaccine
Typhoid vaccine
Pertussis vaccine