People with cardiovascular disease and older adults should get a flu shot each year

Cost: One shot costs 50 to 150 yuan. It should be given once each autumn.
In plain terms: In a trial involving people after a heart attack, the yearly death rate dropped from 4.9% to 2.9% after they received the flu vaccine. For people with cardiovascular disease and older adults, getting one shot each autumn for just 50 to 150 yuan can make a real difference.
Benefit: This trial included 2,571 participants after a myocardial infarction; neither doctors nor patients knew who got the vaccine or the placebo. Over 12 months, the overall death rate was 2.9% in the vaccine group versus 4.9% in the placebo group. The hazard ratio was 0.59, with a 95% confidence interval of 0.39 to 0.89. Cardiovascular death rates also showed a hazard ratio of 0.59. Another study pooled multiple trials and found that flu vaccination lowered the rate of major cardiovascular events to 3.6% from 5.4% in the control group; the relative risk was 0.66, with a 95% confidence interval of 0.53 to 0.83. Cardiovascular death risk showed a relative risk of 0.74, though this fell within the margin of error and was not statistically significant (95% CI 0.42 to 1.30).
Evidence grade: A
Sources:Fröbert O 等 (2021). Influenza Vaccination After Myocardial Infarction: A Randomized, Double-Blind, Placebo-Controlled, Multicenter Trial. Circulation. https://doi.org/10.1161/CIRCULATIONAHA.121.057042 ; Behrouzi B 等 (2022). Association of Influenza Vaccination With Cardiovascular Risk: A Meta-analysis. JAMA Network Open. https://doi.org/10.1001/jamanetworkopen.2022.8873；Demicheli V 等 (2018). Vaccines for preventing influenza in the elderly. Cochrane Database of Systematic Reviews. https://doi.org/10.1002/14651858.CD004876.pub4（备注里说的那份 Cochrane 汇总）
Notes: This recommendation is somewhat controversial. The Grade A rating applies only to people with cardiovascular disease. For otherwise healthy older adults, a Cochrane review offers only limited evidence. Flu vaccination also lowered the seasonal flu infection rate from 6% to 2.4%. The review rated the evidence for infection outcomes as “low” quality and the evidence for mortality as “very low” quality. This review was published in 2018 by Demicheli V et al.