When should we get vaccinated against seasonal flu?

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Varo Baena" "autores" => array:1 [ 0 => array:2 [ "nombre" => "A." "apellidos" => "Varo Baena" ] ] ] ] ] "idiomaDefecto" => "en" "Traduccion" => array:1 [ "es" => array:9 [ "pii" => "S1576988719301487" "doi" => "10.1016/j.vacun.2019.10.002" "estado" => "S300" "subdocumento" => "" "abierto" => array:3 [ "ES" => false "ES2" => false "LATM" => false ] "gratuito" => false "lecturas" => array:1 [ "total" => 0 ] "idiomaDefecto" => "es" "EPUB" => "https://multimedia.elsevier.es/PublicationsMultimediaV1/item/epub/S1576988719301487?idApp=UINPBA00004N" ] ] "EPUB" => "https://multimedia.elsevier.es/PublicationsMultimediaV1/item/epub/S2445146020300029?idApp=UINPBA00004N" "url" => "/24451460/0000002100000001/v4_202105130819/S2445146020300029/v4_202105130819/en/main.assets" ] "en" => array:18 [ "idiomaDefecto" => true "cabecera" => "Vaccination strategy" "titulo" => "When should we get vaccinated against seasonal flu?" "tieneTextoCompleto" => true "paginas" => array:1 [ 0 => array:2 [ "paginaInicial" => "64" "paginaFinal" => "68" ] ] "autores" => array:1 [ 0 => array:3 [ "autoresLista" => "J. Vaqué Rafart" "autores" => array:1 [ 0 => array:3 [ "nombre" => "J." "apellidos" => "Vaqué Rafart" "email" => array:1 [ 0 => "jvaque@telefonica.net" ] ] ] "afiliaciones" => array:1 [ 0 => array:2 [ "entidad" => "Catedrático emérito de Medicina Preventiva y Salud Pública, Universitat Autònoma de Barcelona, Servicio de Medicina Preventiva y Epidemiología, Hospital Vall d’Hebron, Barcelona, Spain" "identificador" => "aff0005" ] ] ] ] "titulosAlternativos" => array:1 [ "es" => array:1 [ "titulo" => "¿Cuándo debemos vacunarnos ante la gripe estacional?" ] ] "textoCompleto" => "The relevance of influenza vaccinationVaccination is the best currently available means of preventing infection by the influenza virus. Its purpose is to reduce the morbidity and mortality occasioned by the infection and also lower its general impact on the population from the social and financial costs involved. Vaccination is particularly important in individuals with a high risk of presenting with complications from flu, and those who are living with them or who administer care. Major scientific evidence exists today proving the increased influenza risk for elderly people<a class="elsevierStyleCrossRefs" href="#bib0125">1,2</a> and for this reason this population group is priority in vaccination programmes against it.The American researchers Glezen et al.<a class="elsevierStyleCrossRef" href="#bib0125">1</a> have made an outstanding contribution regarding influenza in elderly people. After obtaining specific rates of influenza infection by age and complications for 11 consecutive years in Houston, Texas (1978–1989), they determined that people ≥65 years of age presented with an attack rate lower than that of children but that hospitalisations for acute respiratory disease and general mortality were much higher. Czaja et al.<a class="elsevierStyleCrossRef" href="#bib0130">2</a> recently studied the effects of influenza in people ≥65 years of age. To do so they assessed laboratory confirmed cases of flu infection according to age strata in a population group of over 9000 people. The study revealed that the risk of hospitalisation and of pneumonia and death in those hospitalised significantly increased for every 10 year increase in age. In other words, they observed that the risk of complications was clearly associated with more advanced ages. It may therefore be confirmed that although influenza is uncommon in the elderly, its effects may be serious, making it an epidemiological and healthcare issue of importance for the elderly.In the majority of Western countries flu vaccination is recommended for the following population groups,<a class="elsevierStyleCrossRef" href="#bib0135">3</a> which have been subdivided into two large categories:<ul class="elsevierStyleList" id="lis0005"><li class="elsevierStyleListItem" id="lsti0005">•Because of their vulnerability: (a) people ≥60 or ≥65 years of age, depending on the different countries; (b) those who present with a higher risk of complications from influenza, such as patients suffering from chronic diseases or immunodepression and (c) pregnant women.</li><li class="elsevierStyleListItem" id="lsti0010">•Because of their involvement in the transmission of the infection in the community: (a) healthcare or social services personnel; (b)people who provide essential public services, such as fire-fighters and security corps, and (c) international travellers.</li></ul>In contrast, in the United States, with the intention of extending the benefits of vaccination to the whole population, from the 2010–2011 flu seasons onwards it was recommended that all people ≥6 months<a class="elsevierStyleCrossRef" href="#bib0140">4</a> of age should have an annual influenza vaccination.The composition of the vaccines is renewed every year, and aims at including the influenza viruses predicted to circulate during the influenza tracking period and against which the population should be protected. Even when the composition does not vary, i.e. it is the same as the previous year, recommendation for annual vaccination still holds forth, since after vaccination there is a fall in protective antibodies and it is very important to establish a high starting point each year.Administration of the vaccine is parenteral, in a single dose for adults and in two doses for children ≥6 months of age. At present, Finland, Lithuania and United Kingdom have established official vaccination programmes for children using nasal sprays, a formulation that is also in use in the United States.Flu season, influenza tracking period and epidemic waveThe flu season is the period during the year in which flu epidemics associated with influenza viruses circulate. In Europe this starts at the beginning of December and may last until May. The term influenza tracking period stems from public health and refers to the period of the year in which the epidemiology services record and analyse the detected flu cases. It spans from the first week in October until the third week in May of the following year, when surveillance is concluded.<a class="elsevierStyleCrossRef" href="#bib0145">5</a>During each influenza tracking period there is an epidemic wave or period in which the rate of cases rises notably until it reaches a maximum peak from which it then generally rapidly drops. Duration is usually between 9 and 13 weeks. It is somewhat difficult to determine the precise moment in which the epidemic wave begins. Mid autumn is usually when the weekly number of cases increases without the beginning of the wave being specified. A quantitative method is used to determine this. In Spain the epidemic wave is considered to begin when the rate of cases surpasses a baseline threshold determined from the rates prior to the wave from the last 10 influenza tracking periods and the wave is considered terminated when the rate is below the baseline rate.<a class="elsevierStyleCrossRef" href="#bib0145">5</a> For example, the epidemic wave of the 2018–2019 period began in the first week of January, the maximum peak was recorded in the fourth week of that month and the incidence rate returned to pre-epidemic values during the first week of March. The total duration was 9 weeks.<a class="elsevierStyleCrossRef" href="#bib0150">6</a> The week during which for 10 seasons the rise has most often begun is the second week in December.<a class="elsevierStyleCrossRef" href="#bib0145">5</a> In the United States the wave is considered to begin in the first week in which the number of cases is 2% or more than the total accumulation of cases.<a class="elsevierStyleCrossRef" href="#bib0155">7</a>Vaccination campaign or flu vaccination progammeEach year the public health authorities of the country or region organise a vaccination campaign where the people included in the groups recommended for vaccination are invited to go to their corresponding health centres for its administration. This programme lasts 5–6 weeks. The determination of when to start the campaign and how long it should last requires the assessment of the logistic complexities and the cost of its design and maintenance, the characteristics of the groups involved, the ideal interval for the population to take advantage of the opportunities to receive the vaccine, and the most appropriate epidemiological period to achieve effective immune protection in keeping with the foreseeable characteristics of the epidemic wave.It is important to ensure that the population is vaccinated against flu before the onset of the epidemic wave. Vaccinating too early or too late cannot offer the desired protection. Authorised immunological studies have shown that the effective immune response is achieved 14 days after vaccination,<a class="elsevierStyleCrossRef" href="#bib0155">7</a> which means that for the vaccinated to have sufficient protective immunity, there should be a minimum of 14 days between the end of the vaccination campaign and the probable onset of the epidemic wave. Therefore, theoretically, a person who wishes to have maximum immune protection against the next influenza wave would be wise to be vaccinated just 14 days before the foreseeable start of the wave.Countries in the Northern hemisphere offer their vaccination campaigns between mid September and the first week of December, with notable variations. During recent years, many countries have delayed the start of the campaign by two weeks, due to the current argument for leaving vaccination until the foreseeable commencement of the epidemic wave. In Spain the beginning of the 2019–2020 influenza tracking period was fixed between the third week of October and the first week of November.<a class="elsevierStyleCrossRef" href="#bib0160">8</a> In contrast, in Finland, vaccination was only to take place during the month of November.<a class="elsevierStyleCrossRef" href="#bib0165">9</a> Another notable fact is that vaccines should continue to be administered throughout the whole tracking period for people who, for whatever reason, could not receive it during the campaign.In 2015 in the United States the Advisory Committee on Immunisation Practices established the recommendation that all residents in the country ≥6 months of age should, whenever possible, receive vaccination at the end of October.<a class="elsevierStyleCrossRef" href="#bib0170">10</a> In other words, a very limited time period was recommended for vaccination. We believe this proposal was made so that the health agents could bring vaccination closer to the weeks before the beginning of the epidemic wave, since in the United States vaccines are available from the end of July and almost 20% of adults have already been vaccinated by the end of September.<a class="elsevierStyleCrossRef" href="#bib0175">11</a> In the recommendation it states that the population is now used to an extensive vaccination period being available and that its current early initiation in July or August may give rise to a suboptimal immunisation which would not last until the end of the flu season, particularly for elderly people. One disadvantage of shortening the established vaccination period would be the loss of vaccination opportunities.<a class="elsevierStyleCrossRef" href="#bib0170">10</a>Intraseason decline in influenza vaccine effectivenessInfluenza vaccination is moderately effective with regards to its capacity to produce a protective immune response. During the seasons in which concordance between vaccine and circulating strains is high an effectiveness of 60% may be reached for a certain viral subtype. However, in general, it is usually lower than this due to several factors. Apart from a desirable high effectiveness, another expected aim of vaccination is that protection will persist during the whole of the flu season, it will subsist for 5–6 months. However, the immunity achieved wanes over time, an effect which triggers a decline in vaccine effectiveness during the flu season. Because of its importance for public health this waning has been the subject of many different studies, the most relevant of which are commented upon below.Skowronski et al.’s<a class="elsevierStyleCrossRef" href="#bib0180">12</a> review of 14 articles on influenza vaccination in elderly people enabled them to reject the hypothesis that the antibody titre rapidly drops and that levels of seroprotection only lasted 4 months. On the contrary, they discovered that for A(H3N2) and A(H1N1) levels of protection remained high for 5 months or more in most studies assessed, and therefore historic affirmations referring to rapid fall and low duration of protection in the elderly would need to be reconsidered. For the authors, the result was associated with the vaccine limitations, not the low ability of elderly people for antibody induction. As influenza activity usually takes place during a 6–month period the review suggests that administration of a second dose should be considered. However, since the study consisted of a review of articles and was not a specific study based on firm evidence, results have to be interpreted as introductory or for generating hypotheses.In the study conducted by Ferdinands et al.,<a class="elsevierStyleCrossRef" href="#bib0155">7</a> from the CDC, in people of ≥9 years of age, maximum effectiveness was observed not long after vaccination, followed by a drop of 7% one month later for the influenza virus A(H3N2) and B, and a drop of 6% to 11% one month later for A(H1N1)pdm09. The vaccine effectiveness remained above zero for 6 months for the A(H1N1)pdm09 and B virus and for 5months for the A(H3N2). In other words, after vaccination a considerable decline in vaccine protection occurred for all viral subtypes, which after 6 months did not reach zero. These results raised interest and concern. They were discussed by several researchers and this motivated them to design a vaccine strategy called “compressed vaccination period”.<a class="elsevierStyleCrossRefs" href="#bib0185">13–15</a>In Spain, during the 2011–2012 influenza tracking season the epidemic wave began during the second week of December, which is normal, but its ascent was slow, since the peak of maximum activity recorded was as late as mid February. According to the National Centre of Epidemiology, since 1996 this peculiarity had only been observed in two seasons. In the period in question, 70% of the epidemic waves presented with their peak between the end of December and the beginning of January.<a class="elsevierStyleCrossRef" href="#bib0200">16</a> The epidemic of 2011–2012 was singular in character for its late presentation of the influenza wave. This unexpected wave, which occurred 3 months after the vaccination period, resulted in some of the immunised subjects acquiring the infection due to the decline in vaccine effectiveness. This effect was detected by several European studies.<a class="elsevierStyleCrossRefs" href="#bib0205">17–20</a> It was also observed by a multicentre case-control study which studied the 2010–2011 to 2014–2015 seasons, and included over 10,000 cases of laboratory-confirmed influenza infection. For the A(H3N2) subtype the effectiveness obtained was 50.6% 38 days after vaccination, dropping to 0% after 111 days. For the A(H1N1) effectiveness was 55.3% after 54 days and remained between this percentage and 50.3% up until the end of the season. The effectiveness of the virus B dropped to 70.7% 44 days after vaccination and to 21.4% by the end of the season. The authors argued that the fall in effectiveness could be due to the antigentic changes in the virus or the reduced effect of the vaccine, and on the hypothesis that viral changes are usually scarce in the initial stage of the season, the drop should have been present in all stages of the season, as it was in the study by Kissling et al.<a class="elsevierStyleCrossRef" href="#bib0225">21</a> In a study by Young et al.<a class="elsevierStyleCrossRef" href="#bib0230">22</a> on reduced vaccine effectiveness, the authors also rejected the emergence of mismatched viral strains during the flu season as a possible explanation of the drop in effectiveness.Compressed vaccination periodOne strategy employed in many countries is to limit the reduction of protection against vaccine effectiveness decline by delaying the vaccination period by one or two weeks.<a class="elsevierStyleCrossRefs" href="#bib0170">10,11</a> By doing this the vaccination period is moved or compressed towards the beginning of the epidemic wave. In any event it is always essential to maintain a broad time span between both as a precautionary measure against an occasional early beginning to the wave.This strategy limits the decline in effectiveness, and reduces the number of flu cases in the elderly. However, reducing or modifying the period could lower the percentage of people who regularly use the vaccination programme, and an early wave could give rise to an increase in the number of cases.<a class="elsevierStyleCrossRef" href="#bib0190">14</a> According to the recent study by Ferdinands et al.,<a class="elsevierStyleCrossRef" href="#bib0235">23</a> from the CDC, a compressed vaccination period could be beneficial in a typical season, when no more than 38% of the people with appointments for delayed vaccination fail to be vaccinated. They also state that the effects of delayed vaccination are less favourable when total effectiveness of the vaccine is high. The study ends without any clear inclination in favour of compression as they state that it is premature to make recommendations in favour of or against a changes in timing of influenza vaccination programmes based on contemporary knowledge.One further comment is that ideally vaccination should be administered shortly before 14 days prior to the onset of the epidemic wave, which, as expressed above, is the time required by the vaccine to generate protective immunity.<a class="elsevierStyleCrossRef" href="#bib0155">7</a> This would lead to maximum protection at the most appropriate moment, although it is unfeasible, because at present it is impossible to reliably predict the onset of an epidemic wave. Based on this, it would be much less possible to establish a vaccination campaign or vaccination programme for the population, which must always be based on contrasted certitudes. It is a fact that the current vaccination programmes have a fairly late vaccination termination date, at the end of October or beginning of November, and it is our understanding that it is inappropriate to compress this time span further. Whilst waiting for a universal vaccine, at present we can only optimise the time of immunisation to offer the best protection possible.<a class="elsevierStyleCrossRef" href="#bib0240">24</a>Conflict of interestsThe author has no conflict of interests to declare." "textoCompletoSecciones" => array:1 [ "secciones" => array:11 [ 0 => array:3 [ "identificador" => "xres1510440" "titulo" => "Abstract" "secciones" => array:1 [ 0 => array:1 [ "identificador" => "abst0005" ] ] ] 1 => array:2 [ "identificador" => "xpalclavsec1370094" "titulo" => "Keywords" ] 2 => array:3 [ "identificador" => "xres1510441" "titulo" => "Resumen" "secciones" => array:1 [ 0 => array:1 [ "identificador" => "abst0010" ] ] ] 3 => array:2 [ "identificador" => "xpalclavsec1370095" "titulo" => "Palabras clave" ] 4 => array:2 [ "identificador" => "sec0005" "titulo" => "The relevance of influenza vaccination" ] 5 => array:2 [ "identificador" => "sec0010" "titulo" => "Flu season, influenza tracking period and epidemic wave" ] 6 => array:2 [ "identificador" => "sec0015" "titulo" => "Vaccination campaign or flu vaccination progamme" ] 7 => array:2 [ "identificador" => "sec0020" "titulo" => "Intraseason decline in influenza vaccine effectiveness" ] 8 => array:2 [ "identificador" => "sec0025" "titulo" => "Compressed vaccination period" ] 9 => array:2 [ "identificador" => "sec0030" "titulo" => "Conflict of interests" ] 10 => array:1 [ "titulo" => "References" ] ] ] "pdfFichero" => "main.pdf" "tienePdf" => true "fechaRecibido" => "2020-02-06" "fechaAceptado" => "2020-02-19" "PalabrasClave" => array:2 [ "en" => array:1 [ 0 => array:4 [ "clase" => "keyword" "titulo" => "Keywords" "identificador" => "xpalclavsec1370094" "palabras" => array:3 [ 0 => "Influenza" 1 => "Effectiveness" 2 => "Immunisation strategy" ] ] ] "es" => array:1 [ 0 => array:4 [ "clase" => "keyword" "titulo" => "Palabras clave" "identificador" => "xpalclavsec1370095" "palabras" => array:3 [ 0 => "Gripe" 1 => "Efectividad" 2 => "Estrategia vacunal" ] ] ] ] "tieneResumen" => true "resumen" => array:2 [ "en" => array:2 [ "titulo" => "Abstract" "resumen" => "Annual influenza vaccination is especially relevant for older people because of their high risk of complications caused by influenza virus infection. It is important to get the elderly and other groups at risk of influenza derived complications to be vaccinated before the onset of the epidemic activity. Vaccination administered too early or delayed will not allow for desired protection. In northern hemisphere countries, influenza vaccination campaign runs between mid-September and the first week of December, with marked variations across countries.Influenza vaccine has moderate effectiveness in its ability to produce a protective immune response, which is reached within 14 days of having received the vaccine. The immunity achieved is attenuated over time resulting in a marked decline in vaccine effectiveness. One strategy used in many countries to limit this decline is to delay the vaccination period by one to two weeks. This delay either compresses the period towards the onset when the epidemic wave usually begins, so that when it initiates the degree of protective immunity of individuals is high." ] "es" => array:2 [ "titulo" => "Resumen" "resumen" => "La vacunación antigripal anual es especialmente relevante para las personas mayores, debido a su elevado riego de presentar complicaciones por la gripe. Es importante conseguir que los ancianos y las personas de otros grupos de riesgo ante la gripe estén vacunados antes del inicio de la onda epidémica. Una vacunación demasiado precoz o bien retrasada no permitirá conseguir la deseada protección. En los países del hemisferio norte la campaña de vacunación se desarrolla entre mediados de septiembre y la primera semana de diciembre, con notables variaciones.La vacunación antigripal posee una efectividad moderada en cuanto a su capacidad para producir una respuesta inmunitaria protectora, que se alcanza a los 14 días de la vacunación. La inmunidad conseguida se atenúa con el transcurso del tiempo, produciéndose un notable declive de la efectividad vacunal. Una estrategia empleada en muchos países para limitar este declive consiste en retrasar una o dos semanas el periodo de vacunación. Con ello se retrasa o comprime el periodo hacia el momento en que habitualmente comienza la onda epidémica, de manera que cuando esta se inicie el grado de inmunidad protectora de los individuos sea elevado." ] ] "NotaPie" => array:1 [ 0 => array:2 [ "etiqueta" => "☆" "nota" => "Please cite this article as: Vaqué Rafart J. ¿Cuándo debemos vacunarnos ante la gripe estacional? Vacunas. 2020;21:67–71." ] ] "bibliografia" => array:2 [ "titulo" => "References" "seccion" => array:1 [ 0 => array:2 [ "identificador" => "bibs0015" "bibliografiaReferencia" => array:24 [ 0 => array:3 [ "identificador" => "bib0125" "etiqueta" => "1" "referencia" => array:1 [ 0 => array:2 [ "contribucion" => array:1 [ 0 => array:2 [ "titulo" => "Age distribution of patients with medically-attended illnesses caused by sequential variants of influenza A/H1N1: comparison to age-specific infection rates, 1978–1989" "autores" => array:1 [ 0 => array:2 [ "etal" => false "autores" => array:6 [ 0 => "W.P. Glezen" 1 => "W. Keitel" 2 => "L.H. Taber" 3 => "P.A. Piedra" 4 => "R.D. Clover" 5 => "R.B. 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