BACKGROUND Many studies have examined 'non-specific' vaccine effects on infant mortality: attention has been particularly drawn to diphtheria-tetanus-pertussis (DTP) vaccine, which has been proposed to be associated with an increased mortality risk. Both right and left censoring are common in such studies. METHODS We conducted simulation studies examining right censoring (at measles vaccination) and left censoring (by excluding early follow-up) in a variety of scenarios in which confounding was and was not present. We estimated both unadjusted and adjusted hazard ratios (HRs), averaged across simulations. RESULTS We identified scenarios in which right-censoring at measles vaccination was informative and so introduced bias in the direction of a detrimental effect of DTP vaccine. In some, but not all, situations, adjusting for confounding by health status removed the bias caused by censoring. However, such adjustment will not always remove bias due to informative censoring: inverse probability weighting was required in one scenario. Bias due to left censoring arose when both health status and DTP vaccination were associated with mortality during the censored early follow-up and was in the direction of attenuating a beneficial effect of DTP on mortality. Such bias was more severe when the effect of DTP changed over time. CONCLUSIONS Estimates of non-specific effects of vaccines may be biased by informative right or left censoring. Authors of studies estimating such effects should consider the potential for such bias and use appropriate statistical approaches to control for it. Such approaches require measurement of prognostic factors that predict censoring.

中文翻译：

---

在检查疫苗接种对婴儿期影响的研究中，信息检查引入了选择偏见。

背景技术许多研究已经检验了“非特异性”疫苗对婴儿死亡率的影响：已经特别关注白喉-破伤风-百日咳（DTP）疫苗，该疫苗被认为与增加的死亡风险相关。在这种研究中，左右审查都是很常见的。方法我们进行了模拟研究，研究了在存在和不存在混杂因素的各种情况下的右检查（进行麻疹疫苗接种）和左检查（通过排除早期随访）。我们估算了未经模拟和经过调整的危险比（HRs），这些危险比在整个模拟中均取平均值。结果我们确定了在麻疹疫苗接种中进行右检查是有益的情况，因此在DTP疫苗的有害作用方向上引入了偏见。在某些（但不是全部）情况下，根据健康状况进行调整，消除了审查制度造成的偏见。但是，这种调整不能总是消除由于信息审查带来的偏差：在一种情况下，需要对概率进行加权。当健康状况和DTP疫苗接种均与受检早期随访期间的死亡率相关时，由于左检查引起的偏倚出现，并且趋向于减弱DTP对死亡率的有益作用。当DTP的效果随时间变化时，这种偏见更加严重。结论疫苗的非特异性作用的估计可能因信息丰富的右或左检查而有偏差。估计此类影响的研究作者应考虑这种偏见的可能性，并使用适当的统计方法对其进行控制。