Keay Sheila, Poljak Zvonimir, Alberts Famke, O'Connor Annette, Friendship Robert, O'Sullivan Terri L, Sargeant Jan M
Department of Population Medicine, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA.
Animals (Basel). 2023 Oct 3;13(19):3085. doi: 10.3390/ani13193085.
It is unclear if piglets benefit from vaccination of sows against influenza. For the first time, methods of evidence-based medicine were applied to answer the question: "Does vaccine-induced maternally-derived immunity (MDI) protect swine offspring against influenza A viruses?". Challenge trials were reviewed that were published from 1990 to April 2021 and measured at least one of six outcomes in MDI-positive versus MDI-negative offspring (hemagglutination inhibition (HI) titers, virus titers, time to begin and time to stop shedding, risk of infection, average daily gain (ADG), and coughing) ( = 15). Screening and extraction of study characteristics was conducted in duplicate by two reviewers, with data extraction and assessment for risk of bias performed by one. Homology was defined by the antigenic match of vaccine and challenge virus hemagglutinin epitopes. Results: Homologous, but not heterologous MDI, reduced virus titers in piglets. There was no difference, calculated as relative risks (RR), in infection incidence risk over the entire study period; however, infection hazard (instantaneous risk) was decreased in pigs with MDI (log HR = -0.64, 95% CI: -1.13, -0.15). Overall, pigs with MDI took about a ½ day longer to begin shedding virus post-challenge (MD = 0.51, 95% CI: 0.03, 0.99) but the hazard of infected pigs ceasing to shed was not different (log HR = 0.32, 95% CI: -0.29, 0.93). HI titers were synthesized qualitatively and although data on ADG and coughing was extracted, details were insufficient for conducting meta-analyses. Conclusion: Homology of vaccine strains with challenge viruses is an important consideration when assessing vaccine effectiveness. Herd viral dynamics are complex and may include concurrent or sequential exposures in the field. The practical significance of reduced weaned pig virus titers is, therefore, not known and evidence from challenge trials is insufficient to make inferences on the effects of MDI on incidence risk, time to begin or to cease shedding virus, coughing, and ADG. The applicability of evidence from single-strain challenge trials to field practices is limited. Despite the synthesis of six outcomes, challenge trial evidence does not support or refute vaccination of sows against influenza to protect piglets. Additional research is needed; controlled trials with multi-strain concurrent or sequential heterologous challenges have not been conducted, and sequential homologous exposure trials were rare. Consensus is also warranted on (1) the selection of core outcomes, (2) the sizing of trial populations to be reflective of field populations, (3) the reporting of antigenic characterization of vaccines, challenge viruses, and sow exposure history, and (4) on the collection of non-aggregated individual pig data.
目前尚不清楚仔猪是否能从母猪接种流感疫苗中获益。首次应用循证医学方法来回答“疫苗诱导的母源免疫（MDI）能否保护猪后代免受甲型流感病毒感染？”这一问题。对1990年至2021年4月发表的攻毒试验进行了综述，这些试验测量了MDI阳性与MDI阴性后代的六个结果中的至少一个（血凝抑制（HI）滴度、病毒滴度、开始排毒时间和停止排毒时间、感染风险、平均日增重（ADG）和咳嗽）（ = 15）。由两名审阅者对研究特征进行重复筛选和提取，由一名审阅者进行数据提取和偏倚风险评估。同源性由疫苗和攻毒病毒血凝素表位的抗原匹配来定义。结果：同源而非异源的MDI可降低仔猪的病毒滴度。在整个研究期间，以相对风险（RR）计算，感染发病率风险没有差异；然而，MDI猪的感染风险（即时风险）降低（对数风险比 = -0.64，95%置信区间：-1.13，-0.15）。总体而言，MDI猪攻毒后开始排毒的时间大约长半天（平均差 = 0.51，95%置信区间：0.03，0.99），但感染猪停止排毒的风险没有差异（对数风险比 = 0.32，95%置信区间：-0.29，0.93）。对HI滴度进行了定性合成，虽然提取了关于ADG和咳嗽的数据，但细节不足以进行荟萃分析。结论：在评估疫苗效力时，疫苗株与攻毒病毒的同源性是一个重要考虑因素。猪群的病毒动态很复杂，可能包括在实际生产中的同时或相继暴露。因此，断奶仔猪病毒滴度降低的实际意义尚不清楚，攻毒试验的证据不足以推断MDI对感染发病率风险、开始或停止排毒时间、咳嗽和ADG的影响。单株攻毒试验的证据在实际生产中的适用性有限。尽管综合了六个结果，但攻毒试验证据既不支持也不反驳母猪接种流感疫苗以保护仔猪。还需要进一步的研究；尚未进行多株同时或相继异源攻毒的对照试验，相继同源暴露试验也很少见。在以下方面也需要达成共识：（1）核心结果的选择，（2）能反映实际生产群体规模的试验群体大小，（3）疫苗、攻毒病毒和母猪暴露史的抗原特征报告，以及（4）非汇总的个体猪数据的收集。
