As most Americans are aware, the three available COVID-19 vaccines in the U.S. include Pfizer BioNTech, Moderna, and Johnson & Johnson. While all three are extremely effective at preventing severe or even deadly symptoms due to the coronavirus, there are some differences between the three available shots. The Pfizer and Moderna vaccines require two doses for maximum effectiveness whereas Johnson & Johnson only requires one dose for protecting against COVID-19. Many people may not have the option of which vaccine brand to get, but for those that do, some may be wondering, why do Pfizer and Moderna require two doses while the J&J vaccine only requires one dose? And is the two-dose series truly necessary?

As per a recent survey from the CDC, some 5 million people who took the first dose, skipped their second dose of the COVID-19 vaccine. There could be many reasons for this, but the underlying theme in most of them was confusion about the necessity of a second dose.

Science behind the efficacy of the second dose

It is important to know how multi-dose vaccines work (especially Pfizer and Moderna), for us to understand their necessity. The first dose of the mRNA vaccine is meant to inform the body about the infection so that it prepares to attack and eliminate it (scientifically this is referred to as initiating immune response) and the second dose is meant to strengthen this response further by building a memory of the infection. The Johnson & Johnson vaccine uses the more traditional virus-based technology, in which the virus, called “adenovirus”, contains the gene to produce a protein of the SARS-CoV-2 structure in order to elicit an immune system response.

Why is a second shot of the COVID-19 vaccine important?

1. Stronger protection – As per research conducted by the CDC, the first dose of the Pfizer vaccine provides immunity of 60% to 80% against the coronavirus. Additional studies conducted by the CDC state that the Pfizer vaccine's second dose provides immunity of up to 90% against Covid. The official estimate of vaccine efficacy (with both doses) as published by Pfizer is above 91%. These results are proof of the enhanced ability of the second dose to improve the body’s capability to fight the virus. Considering how severe the symptoms and how infectious this virus can be, the second dose provides a more promising outlook in our fight against COVID-19.

2. Taming the pandemic – With countries experiencing one wave after the other and new variants appearing regularly, the only way to tame this pandemic is to prevent its spread. As we’ve witnessed, lockdown helps prevent the spread but is not a permanent solution since it restricts our natural instincts to socialize. The only way to truly protect ourselves and those around us is by getting vaccinated per the recommended schedule. For those who are fully vaccinated, their immune systems prevent the virus from replicating in enough numbers to be contagious and spread. This stage is referred to as herd immunity in scientific circles. As per Serpil Erzurum, MD, Chair of the Lerner Research Institute, some 70 to 85% of our population should be vaccinated to acquire herd immunity.

3. Returning to normal post-Covid – The COVID-19 pandemic not only wreaked havoc on people’s health but also fractured several economies around the world. Millions of people lost their jobs and financial security. For a big proportion of the world population, the future looks bleak. While authorities all over the world are still figuring ways to design the new normal post-Covid, one of the safer ways to reach it is by ensuring complete vaccination of a greater part of our population. The more people who complete their COVID-19 vaccine schedule, the more they become immune and are able to move forward with the new normal. It is in our hands to reduce the stress of the pandemic and the constant fear of a new variant lurking around by getting ourselves vaccinated with two doses as prescribed or the single-dose from J&J.

Why are some people skipping their second dose?

1. Scheduling conflicts – Some people may have something unexpected come up that interferes with their ability to receive the second dose--life happens! According to the CDC, the second dose of the COVID-19 vaccine should be taken preferably after 3 to 4 weeks (3 weeks in the case of Pfizer and 4 weeks for Moderna) and within 6 weeks for maximum efficiency. So, in case you missed your appointment, there is still time to get the second shot. 

2. Fear of repeat side effects - As per the CDC, some people might experience mild side effects of vaccines that may last for a few days like pain in the arm, mild fever, and headache. Some may have heard word-of-mouth that the side effects from the second shot can be more intense, swaying them to skip it. However, most recipients don’t experience severe side effects. Considering the kind of complications Covid patients can face up to 6 months post-recovery, the potential side effects of the vaccine are extremely mild and short-lived in comparison.

 3. Questioning the need – The second dose pumps up the body to fight against the virus. It is like a booster dose to strengthen the body’s immune system response against COVID-19. To get to this level, one must go for the second shot.

Can you get a different vaccine brand for the second dose?

It has not been advised by the CDC or any of the vaccine manufacturers to switch doses. However, you may choose to get the second dose from a different location than your original administration site. If you received your first shot from a pharmacy, the recent collaboration of national and local pharmacies under the Federal Retail Pharmacy Program ensures that you can go to a different pharmacy for your second dose if you choose.

One recent example of the efficacy of vaccination in eradicating a disease through a global vaccination program is smallpox, which used to kill thousands of people every year until a few decades ago. Another disease that is close to eradication due to vaccination is polio. Hopefully, in a short time, we will be able to put COVID-19 behind us due to successful vaccination and herd immunity. As per Israeli historian, professor and a public intellectual and author of Sapiens, Yuval Noah Harari, it is our ability to cooperate in large groups that were instrumental in the success of our species—hopefully, we can continue with this trend!

References:

1. COVID-19 Vaccines that Require 2 Shots | CDC
2. Possible Side Effects After Getting a COVID-19 Vaccine | CDC
3. How Much of the Population Will Need to Be Vaccinated Until the Pandemic Is Over? – Health Essentials from Cleveland Clinic
4. Vaccination - Our World in Data
5. COVID-19 Vaccination Federal Retail Pharmacy Partnership Program | CDC
6. Yuval Noah Harari: “Every crisis is also an opportunity” (unesco.org)
7. Understanding How COVID-19 Vaccines Work | CDC