Yes, briefly. In 19 young doctors wearing a WHOOP strap, heart rate variability (HRV) fell by 13% from baseline Baseline Your own usual HRV level and range, built from weeks of readings taken the same way. Comparing a reading with your baseline says more than comparing it with other people. More about Baseline on the day after their first Pfizer-BioNTech COVID-19 dose and by 9% after the second, while resting heart rate Resting heart rate How many times your heart beats per minute while you are fully at rest. For adults it is usually 60 to 100 beats per minute, and lower in well-trained athletes. More about Resting heart rate and breathing rate Breathing rate How many breaths you take a minute. It moves HRV on its own: slower, deeper breathing makes the beat-to-beat swing larger, and below about 9 breaths a minute it shifts from the HF band into LF. More about Breathing rate did not change (Hajduczok and colleagues, 2021). A 2022 review of five such studies found the same short dip, mostly in RMSSD RMSSD Root mean square of successive differences: an HRV metric built from how much each heartbeat interval differs from the next, in milliseconds. It mainly reflects vagal activity. More about RMSSD , with recovery within up to three days (Kwon and Lee, 2022). The dip is the immune response doing its job, and it is far smaller than the response to the infection itself.
What the wearable studies found
19 doctors, one hospital. The participants were internal medicine residents, average age 29, who wore a strap through both doses. HRV was lowest the day after each dose. Sleep fell on the first night and then rose for up to four days. People who had slept more before the dose showed a bigger HRV change, which the authors took as a possible sign of a stronger response. Side effects were worse after the second dose. It was a small, young, healthy group.
Five studies reviewed. The systematic review found five observational studies published by mid-2022 that reported HRV around COVID-19 vaccination. Four used RMSSD and one an HRV-based stress score. All found short-term changes with quick recovery, within up to three days. Some found the effect larger in women and in younger people. The review rated the studies’ methods as not optimal, and noted that none reported anything about HRV beyond the first days.
Ring data at scale. A study by Oura employees used data from 20,267 members who logged a vaccination to compare the physiological response to confirmed COVID-19 infections and to vaccination across temperature, breathing rate, heart rate, HRV and sleep. Responses to vaccination were smaller in both size and duration than responses to infection, larger after the second dose, and larger in people under 35 than in people over 50; all five measures stayed off baseline for about four days (Pho and colleagues, 2023). This is company data rather than an independent trial.
Why a vaccine moves the number
A vaccine asks the immune system to mount a response, with the same inflammatory messengers that a mild infection would raise. Those messengers push heart rate up a little and ease the vagal brake, so short-term HRV falls for a day or two. The page on HRV when you’re sick describes the same mechanism during a real infection, where it runs for longer and often comes with a clear rise in heart rate and breathing rate as well.
How to read your own data
- Tag the jab. A low morning or two after a vaccine has an obvious cause and should not go into your mental picture of your baseline. The lesson on building your HRV baseline explains why single days mislead.
- Expect a few days. The review found recovery within up to three days, and the Oura data stayed off baseline for about four. If the number is back inside your usual range within a few days, that matches the studies.
- Go easy if you feel it. Soreness, tiredness or a mild fever are reasons for an easy day, as with any low reading that has a clear cause. See should I train when my HRV is low?
- Look elsewhere for longer dips. A trend that stays low for weeks is about something else: sleep, alcohol, training load, illness. Read why your HRV changes so much.
When to talk to a doctor
Mild side effects after a vaccine are common and short. Get medical help for chest pain, breathlessness, a racing or irregular heartbeat, or fainting in the days after a vaccine, whatever your HRV shows. A dip in HRV on its own is not a reason to skip a vaccine or a booster. HRV cannot diagnose anything, and this page is not medical advice.