Vaccines protect against infectious diseases and have long been hailed as a primary public health victory, preventing disease and saving millions of lives. While many Americans anxiously await their turn to be vaccinated against COVID-19, we are beginning to hear, “what now?” from those who have been vaccinated. We sat down with Dr. Donald J. Alcendor to get answers to some of your questions.    

When will I be fully protected from COVID-19 after vaccination?

According to the Food and Drug Administration (FDA) and Centers for Disease Control and Prevention (CDC), the COVID-19 vaccine best protects you against severe disease and death two weeks after you receive your second dose. However, it is important to understand that the vaccine was created to help your body fight off the disease, which means it will help prevent the most severe symptoms of the disease if you become infected. So even after getting full protection from of the vaccine, you may still harbor and transmit the virus to others if you become infected.

Donald J. Alcendor, M.S., Ph.D., Associate Professor, Center for AIDS Health Disparities Research, Division of Microbiology & Immunology, Physiology & Obstetrics & Gynecology, Meharry Medical College

How long am I protected once I am fully vaccinated? Is the coverage different from those who have recovered from COVID-19?

The immune response and immune duration, or the protection you get from the vaccine, can vary from one person to the next. Virus specific antibodies decrease over time, with some preliminary studies suggesting the vaccine will offer six months to a year of protection. We are still learning how long antibodies last with the vaccine, but we have collected some data about how long antibodies last after someone recovers from the virus. In one report, Rita Wilson and Tom Hanks, who were early contractors of the disease, reported that after 11 months they have no detectable antibodies in their plasma. They both participated in a UCLA study that regularly tested them for antibodies to learn more about how long they linger. For Wilson, they lasted 11 months. There are unpublished studies that are not peer reviewed that suggest eight months of detectable antibodies to the COVID-19 virus after infection. 

Why are two doses of the vaccine needed?

Two doses of the Pfizer and Moderna vaccine are recommended for better effectiveness. Some vaccines like the influenza vaccines are given as a single dose and they have a 40 to 60% effectiveness. The Pfizer and Moderna vaccines in clinical trials have shown to be 95% and 94% effective respectively with two doses. 

The number of doses is determined during the course of drug development. Manufacturers will notice if they get a better immune response with one or two doses in the preclinical models and in volunteers during Phase I clinical trials. After coming out of Phase I they will know if two doses are better than one. Higher levels of neutralizing antibodies will likely equal greater efficacy. People vary in their response to the antigen (vaccine) stimulation, which could make two doses more important especially among the elderly. 

What level of protection do you have after the first shot? 

You develop an immune response/antibodies response after the primary dose in one to two weeks; however, the second dose is used to boost or enhance the primary response. The boost usually corresponds to higher levels of antibodies with an expansion of both B- and T- memory cells that can quickly respond and prevent a natural infection by SARS-CoV-2 (the virus that causes COVID-19). Currently it is unknown if a single dose is protective with the currently authorized for emergency use vaccines (Pfizer and Moderna: FDA-EUA). The Johnson & Johnson vaccine is the only single dose coronavirus vaccine that has been authorized for emergency use by FDA. The Johnson & Johnson vaccine has been shown after clinical trials to be 72% effective after a single dose in the U.S.


Some volunteers in the Moderna trial produced low/no antibodies to the vaccine. However, the T-cell response may offer a certain level of protection against natural infection. The antibody response can vary from one person to the next based on age, sex, medical condition, etc.

Once fully vaccinated, can I still contract and spread COVID-19? Will I still need to wear a mask?

If you are infected after being fully vaccinated, the amount of virus in your system will be far less than the amount of virus found in an unvaccinated, infected person. Therefore, you will have a reduced chance of transmitting the infection to another person, but it can still happen. This is why you’re still advised to adhere to CDC guidelines including wearing a mask, maintaining good hygiene and social distancing. The CDC guidance has said that you don’t have to continue with quarantine guidelines.

In addition, individuals with low-immune memory could be susceptible to reinfection. As I shared when discussing antibodies, we’re still determining how long antibodies last after vaccination or infection. In fact, a 25-year-old man was the first case of confirmed COVID-19 reinfection in the U.S., though this was only the fifth confirmed case of reinfection in the world.

Can the vaccine protect against the new variants?

Viral variants are a moving target meaning that they are constantly evolving and changing. To address this concern, researchers are using antibodies from recovered COVID-19 patients to test how the new variants respond to antibodies developed against the vaccine. Moderna and Pfizer-BioNTech can update their vaccines quickly because of their mRNA technology, which can be reprogrammed to target new variants whereas viral vector vaccines are not as easily updated. Moderna has specifically studied how the U.K. and South Africa respond to its vaccine and found that it was about the same for the U.K. variant, but they noticed a diminished response for the South African variant. More research is being done to determine this.

Do you recommend the vaccine to your patients?

I highly recommend the vaccine to all individuals that are eligible. The side effects associated with the vaccine are largely, minor and very similar to the side effects associated with the influenza vaccine.  There should also be no preference for getting a particular vaccine because all of them will protect against developing severe COVID-19 disease and all will prevent you from being hospitalized. 

Learn more about COVID-19 vaccines at You can also listen to OnDemand recordings of our recent Town Hall meetings focused on The Role Vaccines Play in Immunity and Vaccine Distribution

Disclaimer: The information in this article was medically reviewed and accurate at the time of posting. Because knowledge and understanding of COVID-19 is constantly evolving, data or insights may have changed. The most recent posts are listed on the EACH Breath blog landing page. You may also visit our COVID-19 section for updated disease information and contact our Lung HelpLine at 1-800-LUNGUSA for COVID-19 questions.

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