Are COVID-19 systematic reviews up to date and can we tell? A cross-sectional study

COVID-19 led to a rapid acceleration in the number of systematic reviews. Readers need to know how up to date evidence is when selecting reviews to inform decisions. This cross-sectional study aimed to evaluate how easily the currency of COVID-19 systematic reviews published early in the pandemic could be determined and how up to date these reviews were at the time of publication.

We searched for systematic reviews and meta-analyses relevant to COVID-19 added to PubMed in July 2020 and January 2021, including any that were first published as preprints. We extracted data on the date of search, number of included studies, and date first published online. For the search date, we noted the format of the date and where in the review this was reported. A sample of non-COVID-19 systematic reviews from November 2020 served as a comparator.

We identified 246 systematic reviews on COVID-19. In the abstract of these reviews, just over half (57%) reported the search date (day/month/year or month/year) while 43% failed to report any date. When the full text was considered, the search date was missing from 6% of reviews. The median time from last search to publication online was 91 days (IQR 63-130). Time from search to publication was similar for the subset of 15 rapid or living reviews (92 days) but shorter for the 29 reviews published as preprints (37 days). The median number of studies or publications included per review was 23 (IQR 12-40). In the sample of 290 non-COVID SRs, around two-thirds (65%) reported the search date while a third (34%) did not include any date in the abstract. The median time from search to publication online was 253 days (IQR 153-381) and each review included a median of 12 studies (IQR 8-21).

Despite the context of the pandemic and the need to easily ascertain the currency of systematic reviews, reporting of the search date information for COVID-19 reviews was inadequate. Adherence to reporting guidelines would improve the transparency and usefulness of systematic reviews to users.