Abstract: We included six trials published between 2007 and 2014 that randomised 599 adult participants. Study size ranged from 46 to 158 participants. Participants were aged between 18 years and 80 years; we could not derive gender proportions, as participants' sex was not reported in all studies. One study was available in abstract form only. We did not find a significant difference in outcomes between people who exercised and those who did not exercise before receiving influenza vaccination. Pre-vaccination exercises included endurance activities such as walking or using a treadmill, and resistance activities included biceps curls and lateral raises. Five of the studies provided one session of exercise between 25 and 50 minutes. In five studies, exercise was undertaken on the same day as the vaccination. One study provided exercise over a period of eight weeks before vaccination, with one 2½ hour supervised session, plus daily home exercise practice of 45 minutes. Exercise intensity ranged from 55% to 85% of maximal heart rate. Control group participants undertook a range of activities, including quiet rest, sitting, reading, meditation or unspecified activity. One study reported numbers of people who contracted influenza; no significant difference was reported between exercise and no-exercise participants. None of the included studies reported complications related to influenza illness. Only one study, which we assessed as providing low-quality evidence, reported numbers of people who experienced adverse events. This study reported no significant difference in outcomes between people who exercised and those who did not. No studies reported numbers of working days or days lost related to influenza illness. Only two studies reported participant-centred outcomes. Overall, study quality was unclear; we assessed five of the six included studies to have at least four unclear 'Risk of bias' domains (allocation concealment, blinding of outcome assessment, selective reporting and other bias). Insufficient reporting in four studies about selective reporting did not provide enough information to enable judgement; only two studies were included in trials registers. From the available evidence, we found that exercising before influenza vaccination is neither beneficial nor harmful. However, study data were limited and of low quality. Small sample sizes, study design limitations, exercise types, and focus on biochemical rather than participant-centred outcomes strongly influenced our findings.

Plain-language summary: We looked at six studies that involved 599 people aged between 18 and 80 years that assessed exercise before flu vaccination. Exercises included walking or using a treadmill (endurance) and biceps curls and lateral raises (resistance) activities that ranged from 25 to 50 minutes per session. People in five studies did one session of exercise on the day of vaccination; in one study people exercised eight weeks before vaccination. Exercise was supervised in three studies. People not undertaking exercise (control group) were assessed after periods of quiet rest. Three studies did not report study funding sources; one received support from a drug company that donated flu vaccine, one from a professional society, and another from government agencies. We found no differences in numbers of people who caught flu or developed complications between people who exercised and those who did not before flu vaccination. Only one study reported how many people developed flu after exercise and vaccination. No studies reported complications related to flu; only one reported adverse events. None reported numbers of working or other days lost due to flu. No beneficial differences were reported between exercise and no-exercise groups before vaccination. Small numbers of people who were involved in the studies, limitations in study design, and different exercise types meant we were unable to draw robust conclusions about any benefits of exercise before vaccination. There appears to be no benefit or harm from exercising before receiving flu vaccination. Evidence quality was very low or low. More robust study designs that include enough people to enable assessment and analysis of findings may help to determine if exercise before vaccination can reduce numbers of people who develop flu or complications. We found that exercising before influenza vaccination is neither beneficial nor harmful. Small number of people in each included study, many types of exercises, and focus on blood examination instead of participant-centred outcomes strongly influenced our findings.