{"id":1059,"date":"2021-01-23T10:14:23","date_gmt":"2021-01-23T15:14:23","guid":{"rendered":"https:\/\/covidqanda.org\/?p=1059"},"modified":"2021-01-23T10:14:23","modified_gmt":"2021-01-23T15:14:23","slug":"what-is-vaccine-efficacy-if-someone-gets-only-one-dose","status":"publish","type":"post","link":"https:\/\/covidqanda.org\/?p=1059","title":{"rendered":"What is vaccine efficacy if someone gets only one dose?"},"content":{"rendered":"\n

Question:<\/u><\/strong>\u00a0What, if anything, is known about vaccine efficacy for either vaccine if someone only gets 1 shot?<\/p>\n\n\n\n

Answer:<\/span><\/strong>\u00a0We talked about this issue in our Q&A of 1\/6<\/a>.\u00a0 Since then (on 1\/21), CDC updated its clinical guidance<\/a>, stating [bold font is mine]:\u00a0<\/p>\n\n\n\n

“The second dose should be administered as close to the recommended interval as possible [21 days after first dose for Pfizer \/ 28 days for Moderna]. However, if it is not feasible to adhere to the recommended interval, the second dose of Pfizer-BioNTech and Moderna COVID-19 vaccines may be scheduled for administration up to 6 weeks (42 days) after the first dose<\/strong>. There are currently limited data on efficacy of mRNA COVID-19 vaccines administered beyond this window. If the second dose is administered beyond these intervals, there is no need to restart the series.”  <\/p><\/blockquote>\n\n\n\n

Based on currently available analyses of the Pfizer clinical trial data published<\/a> last month in the New England Journal of Medicine (NEJM)<\/em>, we know that the Pfizer vaccine efficacy in the interval between first and second dose is 52% (range: 30% to 68%) (Figure 1)<\/strong>.\u00a0 As authors state, this finding indicates “early protection by the vaccine, starting as soon as 12 days after the first dose.”\u00a0 For Moderna, researchers report in their analysis<\/a> of clinical trial data published last month in NEJM,<\/em>\u00a0“results from a preliminary exploratory analysis suggest that some degree of prevention may be afforded after the first dose.” The small number of infections\u00a0+ short follow-up time\u00a0+ non-random sample\u00a0was too limited to draw firm conclusions about the degree of protection afforded by just 1 dose. That said, in the document Moderna submitted to the FDA<\/a>, they also include efficacy data on those who had only received one dose at the time of interim analysis, showing an efficacy rate of 80% (range: 55% to 92%) with the caveat that the “small, non-random sample and short median follow-up time limits the interpretation of these results.”\u00a0 Both Pfizer and Moderna caution that the duration of protection afforded after just one shot is also unknown beyond the 21 day \/ 28 day interval.\u00a0 Studies designed to answer this question are ongoing.\u00a0\u00a0<\/p>\n\n\n\n

If you’d like to read more, this article from The BMJ,\u00a0<\/em>Covid-19 vaccination: What\u2019s the evidence for extending the dosing interval?<\/a>, and this one from the BBC<\/em>,\u00a0How effective is a single vaccine dose against Covid-19?<\/a>\u00a0are both worth your time!<\/p>\n\n\n\n

Figure 1. Efficacy of Pfizer-BioNTech Vaccine Over Time (upper box inset= after 1st dose, before 2nd dose)\u00a0<\/strong>(from NEJM<\/a>)<\/em><\/p>\n\n\n\n

\"\"<\/figure>\n","protected":false},"excerpt":{"rendered":"

Question:\u00a0What, if anything, is known about vaccine efficacy for either vaccine if someone only gets 1 shot? Answer:\u00a0We talked about this issue in our Q&A of 1\/6.\u00a0 Since then (on 1\/21), CDC updated its clinical guidance, stating [bold font is mine]:\u00a0 “The second dose should be administered as close to the recommended interval as possible […]<\/p>\n","protected":false},"author":1,"featured_media":1060,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"nf_dc_page":"","om_disable_all_campaigns":false,"_monsterinsights_skip_tracking":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":false},"categories":[50,64],"tags":[159,158],"class_list":["post-1059","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-guidelines","category-vaccines","tag-moderna","tag-pfizer","fallback-thumbnail"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"https:\/\/i0.wp.com\/covidqanda.org\/wp-content\/uploads\/2021\/01\/image-22.png?fit=1555%2C1501&ssl=1","_links":{"self":[{"href":"https:\/\/covidqanda.org\/index.php?rest_route=\/wp\/v2\/posts\/1059","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/covidqanda.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/covidqanda.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/covidqanda.org\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/covidqanda.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1059"}],"version-history":[{"count":1,"href":"https:\/\/covidqanda.org\/index.php?rest_route=\/wp\/v2\/posts\/1059\/revisions"}],"predecessor-version":[{"id":1061,"href":"https:\/\/covidqanda.org\/index.php?rest_route=\/wp\/v2\/posts\/1059\/revisions\/1061"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/covidqanda.org\/index.php?rest_route=\/wp\/v2\/media\/1060"}],"wp:attachment":[{"href":"https:\/\/covidqanda.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1059"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/covidqanda.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1059"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/covidqanda.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1059"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}