How COVID vaccines affect sleep, HRV, and resting heart rate data

Originally published on April 27, 2021

COVID vaccines can temporarily change sleep, heart rate variability, Recovery, and resting heart rate, and WHOOP data helps show how long those shifts last. In Episode 121 of the WHOOP Podcast, Emily Capodilupo, Senior Vice President of Research, Algorithms, and Data at WHOOP, breaks down what happened across nearly 51,000 reported vaccine doses, including why second doses hit harder, why younger people often react more strongly, and why the changes usually fade fast.

This conversation is useful if you want a data-based view of what to expect before and after a shot. Capodilupo also explains how mRNA and viral vector vaccines work at a high level, how symptom reports lined up with physiological changes, and how sleep the night before vaccination may affect the response you want from the shot.

To listen to episode 121 in full, head to the WHOOP Podcast on Spotify.

How do COVID vaccines show up in WHOOP data?

COVID vaccines showed up in WHOOP data as a short-lived stress response. Across just under 51,000 reported doses, the main pattern was higher resting heart rate, lower heart rate variability, or HRV, lower Recovery, and one night of worse sleep after vaccination.

That dataset mattered because WHOOP could compare each person's post-shot data against their own baseline, rather than treating everyone as if they started from the same place. Capodilupo said this work built on earlier WHOOP COVID-19 research, including findings on respiratory rate and COVID-19 and broader COVID-19 trends in WHOOP data. By the time of Episode 121 of the WHOOP Podcast, the team had enough scale to compare Pfizer, Moderna, Johnson & Johnson, and AstraZeneca responses side by side.

Capodilupo framed the size of the dataset clearly:

“We’ve had just under 51,000 vaccines reported on WHOOP.”

What you should take away

• WHOOP data showed a repeatable short-term vaccine response in resting heart rate, HRV, Recovery, and sleep.
• The analysis used each person’s own baseline, which makes post-vaccine changes easier to interpret.
• Episode 121 expanded earlier WHOOP COVID-19 research into vaccine response patterns.

If you want to hear Capodilupo unpack how WHOOP identified the main vaccine response pattern, listen to the full episode on Spotify.

Why do second doses hit harder than first doses?

Second doses of Pfizer and Moderna produced stronger reactions than first doses in both symptom reports and WHOOP metrics. The same people who reported more fatigue, chills, or nausea after dose two were also more likely to show a higher resting heart rate, lower HRV, lower Recovery, and more disrupted sleep.

That match between subjective reports and objective data is one of the clearest parts of the episode. Capodilupo explained that the same pattern people had heard about publicly also showed up in the physiological data coming from WHOOP members. The response was still short, but the second dose created a larger bump in the metrics the team tracked.

In the conversation, Capodilupo summed it up this way:

“For both the Pfizer and the Moderna vaccines, people tend to have stronger reactions to the second one than they did for the first.”

What you should take away

• Second doses of Pfizer and Moderna were more likely than first doses to lower Recovery and HRV and raise resting heart rate.
• Symptom reports and WHOOP metrics moved in the same direction after vaccination.
• A stronger second-dose response was common, but it was still brief in this dataset.

If you want to hear Capodilupo go deeper on why second doses changed Recovery and sleep more than first doses, listen to the full episode on Spotify.

Which vaccine responses looked strongest in this dataset?

The strongest reactions in this dataset came from the Moderna second dose, followed by the Pfizer second dose, while the single Johnson & Johnson dose looked similar to a Moderna second dose. For AstraZeneca, WHOOP only had first-dose data at the time, and that first dose looked closer to Johnson & Johnson and the second doses of the mRNA vaccines than to a first Pfizer or Moderna shot.

Once Capodilupo moved from patterns to percentages, the differences became easier to see. For the second Moderna dose, 71% of people saw a Recovery decrease, 65% saw HRV decrease, and 44% had a 10% or greater increase in resting heart rate. For the second Pfizer dose, the same measures were 60%, 52%, and 27%. Capodilupo added that Moderna used about four times the dose of Pfizer, even though public trial data at the time suggested similar protection.

Capodilupo gave the numbers directly on the show:

“We’re seeing 71% and 60% of people experiencing a Recovery score decrease translating to about 44% and 27% having this 10% increase in resting heart rate and 65% and 52% having this decrease in HRV.”

What you should take away

• The Moderna second dose produced the highest rates of Recovery decrease, HRV decrease, and resting heart rate increase in this dataset.
• The Pfizer second dose still produced a clear response, but at lower rates than Moderna.
• The single Johnson & Johnson dose looked closer to a second-dose reaction than a first-dose reaction.
• AstraZeneca first-dose data was available, but second-dose AstraZeneca data was not yet available in Episode 121.

If you want to hear Capodilupo unpack the vaccine-by-vaccine numbers, listen to the full episode on Spotify.

Why do younger people react more strongly to COVID vaccines?

Younger people showed stronger vaccine responses than older groups in both symptoms and WHOOP metrics. In this episode, Capodilupo said younger cohorts were more likely to report fatigue, chills, muscle aches, and fever, and more likely to show increased resting heart rate and decreased HRV.

Those age differences fit the immune-system explanation she gave on the podcast. A younger, healthier immune system may mount a faster, more forceful response to the vaccine target, which can feel unpleasant for a day but still reflect the intended immune activity. Capodilupo pointed to the 18 to 30 group as the clearest example, then added an important timing point: the youngest group also returned to baseline quickly. That short rebound stood in contrast to earlier WHOOP COVID-19 illness research and to the first-dose analysis shared in Episode 109 of the WHOOP Podcast.

Capodilupo explained the age pattern this way:

“We’re seeing a much stronger reaction in younger people than we are in older groups.”

What you should take away

• Younger WHOOP members were more likely to report symptoms and show stronger HRV and resting heart rate shifts after vaccination.
• Capodilupo linked that pattern to a stronger immune response, especially in people ages 18 to 30.
• Even in younger people, the vaccine response usually returned to baseline by the second night in this dataset.

If you want to hear Capodilupo go deeper on age-related vaccine responses and why younger people bounced back quickly, listen to the full episode on Spotify.

How should you plan sleep, training, and work around a vaccine?

The simplest plan is to expect an easier 24 hours after Johnson & Johnson, AstraZeneca, or a second Pfizer or Moderna dose. Capodilupo said most people getting a first Pfizer or Moderna shot could expect to feel fine, but the second dose or single-dose vaccines were the situations where it made sense to clear space for more sleep, less training, and lighter work if possible.

Fatigue was the most common symptom across vaccines. Capodilupo said just shy of 80% of people reported fatigue after the second Pfizer and Moderna doses and after the first AstraZeneca dose. Sleep also took a short hit. Total sleep time fell across vaccines, and restorative sleep dropped too. After the second dose, about 50% of Moderna recipients and 37% of Pfizer recipients had lower-quality sleep, but Capodilupo said that disturbance usually lasted one night.

Her practical advice lined up with that timeline: do not plan a very hard workout, get to bed earlier if you can, stay hydrated, eat well, and protect sleep the night before. That final point lines up with prior vaccine sleep research suggesting sleep deprivation before vaccination can reduce antibody response, and it fits broader WHOOP work on sleep measurement and sleep consistency during COVID-19.

Capodilupo put it plainly:

“It’s probably a good idea to plan to be nice to yourself in the 24 hours after the vaccine.”

What you should take away

• Fatigue was the most common post-vaccine symptom in this WHOOP dataset.
• One easier day after a second mRNA dose or a single-dose vaccine is a sensible plan.
• An earlier bedtime, lighter training, hydration, and a good night of sleep before the shot fit the patterns Capodilupo described.
• Sleep disruption after vaccination usually lasted one night in this dataset.

The bottom line

• WHOOP data showed that COVID vaccines commonly caused a short-term rise in resting heart rate and short-term drops in HRV, Recovery, and sleep quality.
• Second doses of Pfizer and Moderna produced stronger reactions than first doses in both symptom reports and WHOOP metrics.
• The Moderna second dose produced higher rates of Recovery decrease, HRV decrease, and resting heart rate increase than the Pfizer second dose in this dataset.
• The single Johnson & Johnson dose looked closer to a second-dose response than to a first-dose response.
• Younger people showed stronger vaccine responses than older groups, which Capodilupo linked to stronger immune activity.
• The post-vaccine response in WHOOP data usually returned to baseline by the second night after the shot.
• Fatigue was the most commonly reported symptom, and short-term sleep disruption was common after vaccination.
• A lighter training day, more sleep opportunity, hydration, and a good night of sleep before the shot matched the practical guidance in Episode 121.

Frequently asked questions about things discussed in this episode

How does WHOOP show a vaccine response in Recovery, HRV, and resting heart rate?

WHOOP showed a vaccine response as a short-term increase in resting heart rate and short-term decreases in HRV, Recovery, and sleep quality, usually appearing the night after vaccination.

What does WHOOP data suggest about first versus second COVID vaccine doses?

WHOOP data suggested that second doses of Pfizer and Moderna produced stronger responses than first doses, with larger shifts in Recovery, HRV, resting heart rate, and sleep.

How does WHOOP show vaccine-related sleep changes?

WHOOP showed vaccine-related sleep changes as lower total sleep time and lower restorative sleep after vaccination, with the largest changes after second doses and a return toward baseline after one night for most people in this dataset.

What does WHOOP data show about age and vaccine response?

WHOOP data showed that younger people were more likely to report symptoms and more likely to show stronger increases in resting heart rate and stronger decreases in HRV after vaccination.

How can WHOOP help you plan the day after a vaccine?

WHOOP can help you plan the day after a vaccine by showing whether Recovery, HRV, resting heart rate, and sleep shifted from baseline, which supports a lighter training load and more sleep opportunity when the response is stronger.

What does WHOOP say about getting vaccinated after having COVID-19?

WHOOP data in this episode did not answer that question on its own. Capodilupo said public health guidance at the time recommended vaccination even after prior COVID-19 infection.

For vaccine days, WHOOP gives you a baseline-based view of sleep, HRV, resting heart rate, and Recovery so a one-day response is easier to recognize and less likely to feel confusing.