{"id":11686,"date":"2025-10-28T05:34:24","date_gmt":"2025-10-28T09:34:24","guid":{"rendered":"https:\/\/blogs.nejm.org\/hiv-id-observations\/?p=11686"},"modified":"2025-11-03T16:07:35","modified_gmt":"2025-11-03T21:07:35","slug":"two-covid-vaccine-studies-one-actionable-the-other-not-so-much","status":"publish","type":"post","link":"https:\/\/blogs.nejm.org\/hiv-id-observations\/index.php\/two-covid-vaccine-studies-one-actionable-the-other-not-so-much\/2025\/10\/28\/","title":{"rendered":"Two Covid Vaccine Studies — One Actionable, the Other Not So Much"},"content":{"rendered":"

\"\"As we await the results of placebo-controlled Covid-19 vaccine studies, what are we clinicians to do when our patients ask us whether they should get a booster this fall? What once was a no-brainer in the early days of limited immunity to the virus — and the spectacular results of the first placebo-controlled trials<\/a> — is now a much more nuanced clinical question. Essentially 100% of the population has had either Covid or been vaccinated or both, the disease is on average less severe, the vaccines do have side effects — and who wants another shot anyway?<\/p>\n

Now, along comes one of the more clever (cleverer?) observational studies to date addressing this question.<\/p>\n

Published here in the New England Journal of Medicine<\/em><\/a>, researchers from the U.S. Department of Veterans Affairs evaluated the 2024\u201325 Covid-19 vaccine among more than 160,000 veterans who received it on the same day as their flu shot, compared with 130,000 who received the flu shot alone. Participants were followed for six months.<\/p>\n

This inclusion of the flu shot only group was absolutely critical, as it diminished the inevitable bias of many observational vaccine studies — which is that those who choose to be vaccinated may intrinsically have more healthy behaviors overall, and that these differences lead to better outcomes, not the vaccines. It’s a form of confounding that no amount of statistical pyrotechnics can completely remove.<\/p>\n

Indeed, the “Table 1” of the study, showing baseline characteristics, showed that the group getting the Covid-19 vaccine was quite similar to those who did not, even before statistical adjustment. Hooray. The study included a very typical VA population: age in the early 70s, over 90% were men, and about 18% smoked.<\/p>\n

The results?<\/p>\n