It is an open secret that I am somewhat of a quantified self nut. For many years, I measure a lot of data using different wearables and devices. Currently, I wear a Garmin Fenix 6 Smartwatch, and in addition, I recently got an Oura Smart Ring (more in a recent Podcast round).

Despite being a skeptic for the longest time, I even convinced my wife to wear the Garmin Vivomove that I got her. Now she is almost as obsessed as I am with the heart rate variability-based metrics Garmin provides.

Health wearables have come a long way, and we are now at a point where they can provide valuable insights into our bodies and actionable advice to improve our health, not just gamified step challenges.

Heart rate variability (HRV), the variance in time between your heartbeats, has over the past few years become a key metric in analyzing your overall fitness. HRV is very individual to a person and is highly reactive to all kinds of impulses, such as hydration, alcohol, sleep, physical activity, stress, and sickness. Especially when measured over time, your HRV value can provide a reliable data-based assessment of your health status. Garmin expresses your HRV over time in the form of a Body Battery (with a value between 5-100%), the Oura ring calculates a Readiness Score in the morning and gives a nightly average value for the HRV in ms.

Excellent examples of the quality of heart rate variability measures from current consumer devices are my wife's and my records from last week when both of us received our second dose of the BioNTech-Pfizer-Fosun mRNA Covid Vaccine.

Hong Kong – So far, a COVID but not a vaccination success story

In Hong Kong, we luckily avoided a larger COVID community outbreak so far. As per the middle of May 2021, Hong Kong ranks 148th by the total number of COVID cases, with less than 12k and just 210 deaths. The cases per capita ranking is even better; 171 other countries and regions had more COVID cases than the Special Administrative Region.

I wrote about it last year, and I still believe that Hong Kong has dealt so well with the pandemic mainly due to very proactive community response. Most people were already wearing a mask in public, long before it became mandatory.

Hong Kong people are much less proactive, though, when it comes to getting vaccinated. Hong Kong's community vaccination centers remain utilized way below their capacity, and the government reacted early by opening the booking system for the general public, not just high-risk groups. First, all residents older than 30 could register, then even all residents above 16 years could get the shot.

In Hong Kong, the vaccination is free; you can choose between the Sinovac shot and Cormirnaty, developed by BioNTech and Pfizer and distributed by Fosun Pharma.

Neither my wife nor I have family in Hong Kong. With the ability to travel ranking quite high on our hierarchy of needs, we decided pretty early that we would take the vaccination once available. Doing my research on the vaccines, I decided that taking one of the mRNA vaccines would be my preference.

Once the booking system was open, we booked our appointments to receive the Cormirnaty shot. Our bookings were for two Thursdays, both 6:30 pm, the two shots spaced precisely three weeks apart.

Two jabs: same poke, different impacts

For both of our appointments, my wife and I traveled to the Hong Kong International Airport, where a community vaccination center set up shop in a ground transportation lounge. Including the check-in, signing several disclaimers, getting the shot, and resting mandatory for 15 minutes after the jab, we were in and out of the center within half an hour.

After the first jab, I did not feel anything other than a slight soreness in my left arm. It felt as if I had met one of those overly enthusiastic shoulder punching guys from high school. After getting the shot Thursday evening, I worked out the next day during lunch break and was just fine.

My Garmin data for the first shot was relatively unremarkable. While I did not fully recharge overnight, my energy level on the day after the shot stayed fairly stable over the office day, despite working out over the weekend.

The day of the second shot was a home office day, so I did an 8km run in the morning. Just as three weeks earlier, I met my wife at the airport around 6:15 pm, and we got our second shot, got takeaway dinner, and went to bed at our normal time.

Waking up the day after, I felt ok. Garmin had me at a 70 % body battery; Oura showed a Readiness Score of 83 (good), a slightly elevated resting heart rate (51 compared to the usual 43-47 bpm and it registered a light increased body temperature (+0.2 degrees Celsius).

None of these values were unusual on the day after a longer mid-week run. In what soon turned out to be a clear error in judgment, I had booked a lunchtime training at my PT gym. The session, an evaluation training with a new coach, was not particularly pretty. My heart rate was higher than usual. I nearly choked breathing in my breath under the mask, and everything felt a bit more difficult than usual. My left arm also felt not fantastic, including my armpit that was slightly swollen.

After the training, Garmin had me at around 40 % remaining Body Battery, but this value continued to fall steadily over the afternoon. When I left my office at 7 pm, my body battery value flatlined at 5%, the lowest value on the Garmin scale.

My wife was not feeling much better; she sent me green-faced puking smileys as early as 11 am, and apparently, she felt alternatingly hot or had the shivers over the whole day.

We had a light dinner and called it a day early. We slept by 10 pm. I woke up during the night a few times, soaking wet in sweat and still feeling cold. Around 7:30 am, we woke up.

As it turned out, despite getting a generous amount of sleep, both of us were still at Garmin's minimum Body Battery of 5%; apparently, the rest did not help us to recover.

Oura’s data was not much better: my Readiness showed 38; heart rate variability was a mere 37ms, body temperature was 1.7 degrees Celsius higher than my base right, which should have brought me into fever territory. Resting heart rate was 61, another ten beats above the already elevated Friday.

I was not feeling deadly sick, but definitely felt the lack of energy and that I have drained myself further during sleep, instead of recovering.

Other than a bit of housecleaning, we didn't do much all Saturday. I spent time doing some changes to this very website (did anybody realize I added a books section?) and finished reading a book (Michael Lewis excellent Premonition: A Pandemic Story, Amazon affiliate link here). In the late afternoon, we went for a one-hour walk, at a moderate pace. While my wife's battery stayed flat all day, my HRV at least showed signs of recovery, reaching a high of 11 in the early evening.

As quickly as it came, our vaccination-induced battery discharge came to an end. I woke up on Sunday morning with a full 100 on my Body Battery score; Oura gave me a readiness score of 82, my HRV was back at 69 ms, my temperature -0.2 degree below average, and my resting heart rate back to a pretty standard 46 bpm.

My swollen left armpit lymph nodes took another day to recover. By Monday night the swelling normalized and I felt all normal again.

From what I heard and witnessed amongst friends, colleagues, and family members, our side effects were pretty typical and somewhat in the middle of the spectrum. Some colleagues of mine did not feel anything after the second shot, others were pretty much down for 2-3 days.

In a way, a bit of a side effect from vaccination has almost an encouraging effect, it just feels as if you are building antibodies.

Whether you take the shot or not, is up to you. Make an informed decision, but be aware that in the end, it helps all of us, if the virus is contained.

I hope our example didn’t scare you off. Our side effects were not a big deal, actually quite similar to the aftermath of running a marathon or trail running ultra. I have not yet encountered anybody personally who suffered much worse side effects.

If you already have taken your shot and you happen to wear any health wearable, shot me a message. I am very curious if you produced similar values as we did.