Pfizer-BioNTech and Moderna Vaccines
The mRNA vaccines come in two doses. The first dose of the vaccine helps prepare your immune system and the second dose provides most of the immunity. Once you receive both doses of the vaccine, it will likely take several weeks for your body to develop immunity. Both doses are important to ensure full protection.
A study published in the New England Journal of Medicine in December found that protection from the Pzifer-BioNTech vaccine starts 12 days after the first shot and that it reaches 52% effectiveness a few weeks later. A week after the second vaccination, the effectiveness rate hits 95%.
Researchers are exploring whether the efficacy after the first dose is better than seen in the clinical trial. A recent study from Israel released in the Lancet, looked at 9,109 vaccinated and unvaccinated health care workers. They found:
The Moderna trial reported a protection rate of 51% two weeks after the first immunization and 94% two weeks after the second dose.
There has been recent discussion among public health officials, looking at population-level strategy, whether it is better to vaccinate more people with one dose (with lower efficacy) or a smaller group of people with two doses (with high efficacy). At this time, the recommendation remains that individuals receive two doses of the Pfizer-BioNTech or Moderna vaccine.
Johnson & Johnson Vaccine
The Johnson & Johnson is currently a one dose vaccine. In November 2020, Johnson & Johnson initiated a trial (ENSEMBLE 2) for a two dose regimen of the vaccine however results are not yet available.
Updated: March 1, 2021