Disclaimer: This should not be taken as medical advice as I am just sharing my experience as someone who had taken 2 Pfizer shots and decided to take Moderna as my booster.
I had my first and second vaccinations back in March and April 2021 and that made me eligible for my booster yesterday (19 October). I made the conscious effort to “mix” vaccines by going for Moderna even if it meant that I had to travel slightly further to a vaccination centre that carries Moderna when there’s already a Pfizer vaccination centre within a 5-minute walk from my home. I am also aware of the generally worse side effects based on anecdotal accounts from Moderna recipients.
So why did I still choose to bring this upon myself?
First of all, I have no doubt that Pfizer and Moderna are both great mRNA vaccines. They both greatly reduce the chances that one will get hospitalised due to severe symptoms from Covid-19. However, in the recent months, there has been early reports that Moderna is more effective than Pfizer against the Delta variant.
In a study of more than 50,000 patients in the Mayo Clinic Health System, researchers found that the effectiveness of Moderna’s vaccine against infection had dropped to 76 per cent last month – when the Delta variant was predominant – from 86 per cent early this year.
Over the same period, the effectiveness of the Pfizer-BioNTech vaccine had fallen to 42 per cent from 76 per cent, researchers said.
Historically, there were findings of vaccine mixing (heterologous prime-boost) could be more immunogenic than single vaccines (homologous prime-boost). While such a study has yet to be conducted on a Pfizer-Moderna combination, authorities around the world have begun allowing mixing of vaccines to ease the burden on logistics and supplies.
In Singapore, our authorities view mRNA vaccines as “similar” and have therefore officially allowed the mix as of 17 September 2021.
Side effects of mixing Pfizer and Moderna Vaccines
Before going for the booster shot, I tried searching for side effects of mixing the two vaccines but without success. So here’s my account of the 36 hours post vaccination:
19 October 2021
9:30am: I arrived at the vaccination site ahead of my 10am appointment. I was made to acknowledge that I am switching from Pfizer to Moderna – twice. Once at the registration counter and then at the vaccination booth.
9:36am: Vaccination done. Time for the 30-minute on-site observation.
10:06am: Called to the discharge counter to check if I’m okay. All good. I then took a 4km casual walk home (strenuous exercise is not allowed so I made sure that it was a casual stroll).
I technically had the day off from work (vaccination benefit) so I chilled for the most part of the afternoon.
4pm: Short nap – no fever yet.
6pm: Felt a bit lethargic. No fever yet. Unable to get up to send my daughter for her piano class.
7pm: Got up for dinner. No fever yet. Realised that there’s some work to be done.
8pm: Slight fever at 37.9 C.
10pm: Fever at 38.5 C.
11pm: Fever at 39 C, chills kicking in. This continued through the night.
20 October 2021
7am: A lot of pressure on my entire face – like it’s going to explode. I could barely wake my kids up for school. Temp: 38.9 C.
3pm: I only got up at 3pm and temperature was 38.1 C. Attended a few meetings and left home to get my medical leave to cover my absence for the good part of the work day.
7pm: Temperature at 37.6 C (Might be the paracetamol that I finally took)
10pm: Temperature 38.4 C + chills. Here we go again.
I’ll update this post until I’ve stopped experiencing any effects of the vaccination.
Conclusion about mixing Pfizer / Moderna for booster shot
It has always been anecdotally known that Moderna recipients suffer longer fevers, headaches and chills compared to Pfizer recipients. This is why I am not at all surprised if my symptoms is going to go on for another day or two. This is within my expectation and I made that informed choice.
Should you mix vaccines? My personal opinion is yes. Mixing vaccines could potentially offer a wider spectrum of coverage. Even if it does not offer significant benefits, there should not be any ill effects of mixing the vaccines otherwise this practice would have been banned around the world. At the end of the day, this is your personal choice. Mixing or not, just get your 2 +1 vaccinations done!