TL;DR: The Janssen vaccine is still definitely better than no vaccine at all, but the mRNA vaccine appears to be safer and more effective.
If you haven’t gotten your first vaccine yet, Pfizer or Moderna is preferred. If you already got the first Janssen shot but haven’t yet got your booster, the mRNA is recommended for your booster.
The CDC now recommends an mRNA vaccine (like Pfizer or Moderna) over the Janssen (also called Johnson and Johnson or J&J) COVID-19 vaccine. This is a change in the recommendation and comes after a recent meeting of the Advisory Committee on Immunization Practices (ACIP).
So, why the change? The ACIP met on 12/16/21 and reviewed new data from our extremely robust safety and efficacy monitoring systems. This info, along with increased access to mRNA vaccines, has altered the risk-benefit calculus a little bit.
Adenovirus vaccines (like Janssen or AstraZeneca) have been associated with a very rare syndrome called thrombosis with thrombocytopenia syndrome (TTS). This is when a person both develops blood clots (thrombosis) and low platelets (thrombocytopenia). Platelets are the cells in the blood that clump together to form blood clots. When someone doesn’t have enough platelets, they are at risk of dangerous bleeding. TTS is a rare and dangerous condition when someone can both form blood clots and have bleeding. If this develops after Janssen vaccination, the blood clots form in unusual places, like the central venous sinuses in the brain. The venous sinuses are veins that drain blood from the brain back to the heart. Blood clots here can cause strokes and bleeding into the brain.
The risk of TTS after the Janssen vaccine varies by age and sex assigned at birth. Women aged 30-39 have the highest risk (about 1 case for every 100,000 doses administered). Of people who develop this condition, about 15% will die from it and about 17% will need to spend time in a skilled nursing or rehabilitation facility after being discharged from the hospital. TTS has not been associated with mRNA vaccines.
The Janssen COVID-19 vaccine has also been associated with acute inflammatory demyelinating polyneuropathy, or AIDP (previously known as Guillain-Barre syndrome). This is a neurological disorder that happens when the body’s immune system attacks the lining of the nerves. Bacterial and viral infections (including COVID-19) are the most common causes of AIDP, but it has been reported with the Janssen vaccine. This is super rare (for example, for women age 18-49, we would estimate about 5 cases of AIDP per 1 million Janssen doses given). For those few folks that do develop it, about 1% will die and 10% will require breathing tubes at some point during the illness.
The Janssen vaccine also does not appear as effective at preventing COVID-19 hospitalizations as the mRNA vaccines. For example, between March and August 2021, the vaccine effectiveness (VE) for the Janssen vaccine was 73% for 18-49 year-olds, 69% for 50-64 year-olds, and 76% for folks aged 65 and up. Don’t get us wrong: That is still great. That’s still a TON of hospitalizations and ultimately death prevented by getting the Janssen vaccine. However, the estimates for the VE of the mRNA vaccines were about 92% for 18-49 year-olds, 92% for 50-64 year-olds, and 88% for folks aged 65 and up.
Long story short, while severe complications from any COVID-19 vaccine are super unlikely, the mRNA vaccines appear to be safer and more effective than the Janssen vaccine. The Janssen vaccine is DEFINETLY STILL BETTER THAN NO VACCINE AT ALL. Let’s again take women age 18-49. For every 9 cases of TTS and 5 cases of AIDP per million doses, 3,729 hospitalizations will be prevented. For older folks, that number is even more impressive. For women over 65, for every 2 cases of TTS and 9 cases of AIDP per million doses given, 24,159 hospitalizations will be prevented. So, if it is the only one available, getting the Janssen vaccine is most definitely safer than getting infected with COVID-19. There is no question about this. But, if an mRNA vaccine is available and you don’t have a contraindication to it (like a severe allergic reaction to it or one of its components), it is the preferred choice.
So here are some take home points:
1) If you haven’t started your vaccines yet for COVID-19, the mRNA vaccines are preferred.
2) If you don’t have access to an mRNA vaccine, get the Janssen vaccine! It will still reduce your risk of infection, hospitalization, and death.
3) If you already got the Janssen vaccine but haven’t gotten your booster, you are recommended to get an mRNA shot as your booster 2 months after the Janssen vaccine.
4) If you already got the Janssen vaccine AND booster, you don’t have to start again or rush out to get an mRNA shot! You are considered fully vaccinated.
5) Our safety monitoring system works and helps us keep our recommendations up to date.
6) Any vaccine is still better than no vaccine. Please get vaccinated and encourage those around you to get vaccinated too.
Stay Safe. Stay Sane.
Those Nerdy Girls
Ok, so that was super long. But if you want more, here are the links!
