We're learning more about the Pfizer [1] and Moderna COVID-19 vaccines [2] every day, and one thing we already know is that both vaccines require not one but two doses (aka two shots) to be fully effective. You're not alone if you're confused about why, especially when you realise this makes an already difficult task (vaccinating the entire world) even more difficult (vaccinating the entire world . . . twice.) POPSUGAR talked to Carlos Malvestutto, MD, MPH, an infectious disease doctor at the Ohio State University Wexner Medical Centre [3], to find out why it's crucial that you return to get that second dose.
Why Do I Need 2 Doses of the COVID-19 Vaccine?
Put simply, getting a second dose of the Pfizer and Moderna vaccines leads to a significant increase in COVID-19 antibody levels compared to a single dose, Dr. Malvestutto said. (The two doses are identical in size.) Why are more COVID-19 antibodies a good thing? Because they're the proteins your body makes neutralise the coronavirus pathogen [4], eliminating the virus before it leads to disease. Data has shown that the more COVID-19 antibodies you have [5], the better protected you are.
So when early trials showed higher levels of antibodies after a second shot, Pfizer and Moderna decided to make their vaccines double-dose. It comes down to simple reasoning. "We know that a second dose leads to a higher concentration of the neutralising antibody that we want the body to produce," Dr. Malvestutto said. "So, the higher the neutralising antibody concentration, the better the protection is." It's not a novel concept; the Hepatitis B and Human Papilloma Virus (HPV) vaccines are also given in multiple doses to maximise antibody response.
It's worth noting that not all of the developing COVID-19 vaccines require two doses. The Johnson & Johnson vaccine, currently in Phase 3 trials, may only require one shot, though the company is also conducting a study using two doses [7]. "In preclinical trials, [Johnson & Johnson] found that they were achieving adequate levels of the production of these neutralising antibodies," Dr. Malvestutto explained.
Do I Need to Get Both Doses of the COVID-19 Vaccine?
Pfizer and Moderna are two-dose vaccines, so receiving both doses is crucial in ensuring maximum effectiveness. "People should not count on, 'Okay, I had one, that's good enough,'" Dr. Malvestutto explained. "Now that we have a vaccine, let's make sure that we get the full protection that we can get from this."
Yes, it's more challenging to get two doses, on both an individual and global level. "We are going to do everything possible to make it as easy and as painless as possible for people to come back for that second shot," Dr. Malvestutto stressed. While one shot will provide some protection, getting both doses gives your body a significantly stronger defence. "If we know that it works best with two doses," Dr. Malvestutto said, "then get the two doses."
POPSUGAR aims to give you the most accurate and up-to-date information about the coronavirus, but details and recommendations about this pandemic may have changed since publication. For the latest information on COVID-19, please check out resources from the WHO [8], CDC [9], and local public health departments [10].
