Can you get flu and COVID shots at the same time? What the trials show

Yes — the evidence from randomised trials supports getting a flu shot and a COVID-19 shot at the same visit, usually one in each arm. Two UK trials set out to test exactly this question, because giving both together in a single appointment eases the strain on clinics and means fewer people fall through the cracks between two separate trips. Both found the combination broadly safe and immunologically sound, with some caveats worth knowing.

The trial built to answer the question

ComFluCOV was a multicentre, randomised, controlled phase 4 trial that recruited 679 adults between 1 April and 26 June 2021 [s1]. Participants who had already received a first dose of either the ChAdOx1 or the BNT162b2 COVID-19 vaccine were randomly assigned to get an age-appropriate influenza vaccine either alongside their second COVID dose or three weeks later, with a placebo injection standing in on the other occasion so neither participants nor investigators knew which visit carried the real flu shot [s1].

The primary question was reactogenicity: whether giving both together produced more of the systemic reactions — fever, aches, fatigue — that people report in the week after vaccination. The trial set a non-inferiority margin of 25%, meaning co-administration had to add no more than that to the rate of reactions to pass [s1]. Non-inferiority was met in four of the six vaccine combinations tested; in the other two the confidence interval crossed the margin, so the result there was inconclusive rather than a signal of harm [s1]. Most systemic reactions were mild or moderate, and rates of local and unsolicited systemic reactions were similar between the groups [s1]. There was one serious adverse event considered related to the trial — a hospitalisation with severe headache. Crucially, immune responses to both vaccines were not adversely affected by giving them together [s1].

A second trial, with a nuance

A substudy nested inside the phase 3 trial of the Novavax protein vaccine (NVX-CoV2373) tested the same idea in 431 people: 217 received the COVID vaccine plus a licensed influenza vaccine, and 214 received placebo plus the influenza vaccine [s2]. Here the reactions were more common in the co-administration group than among those given the COVID vaccine alone: injection-site tenderness in 64.9% versus 53.3%, injection-site pain in 39.7% versus 29.3%, fatigue in 27.7% versus 19.4%, and muscle pain in 28.3% versus 21.4% [s2]. Serious adverse events were low and balanced between the groups, with no anaphylaxis or deaths in the substudy [s2].

The immunology carried a genuine caveat. Co-administration did not change the immune response to the influenza vaccine, but it did reduce antibody responses to the COVID vaccine [s2]. Whether that dip matters for protection is the key question, and the trial's efficacy figure is reassuring on that point while also being imprecise: vaccine efficacy against COVID-19 in the substudy was 87.5%, but with a wide 95% confidence interval running from −0.2 to 98.4 because the substudy was small [s2]. The honest reading is that protection appeared preserved, but the substudy was not large enough to measure it tightly.

What the two trials add up to

Taken together, the trials point the same way: giving a seasonal flu vaccine at the same appointment as a COVID-19 vaccine did not raise safety concerns beyond the ordinary sore arm and short-lived aches, and it left the flu response intact [s1][s2]. The main trade-offs are a somewhat higher chance of those local and systemic reactions in the days afterward, and, in the protein-vaccine substudy, a reduction in COVID antibody levels whose clinical importance the study could not fully resolve [s2]. Both trials were conducted in adults, so they do not speak directly to children.

What this does and does not tell you

These findings describe what happened on average in trial populations; they are not personal advice, and they do not tell any individual which vaccines they are due or when. The vaccines themselves change composition each season, and recommendations differ by country and by age. What the evidence does establish is that the practical convenience of a single visit does not come at the cost of a safety problem the trials could detect. Anyone weighing the timing of their shots — together or spaced apart — should confirm what they are eligible for with a clinician or pharmacist who can see their record.