More Answers to Your COVID-19 Vaccination Questions
Vaccination efforts are racing against community spread of COVID-19. As more people become eligible for vaccination, a UArizona immunobiologist answers common questions about what to expect after the shot.

By Mikayla Mace Kelley, University Communications
Feb. 16, 2021

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Volunteers assist drivers at COVID 19 Vaccine Point of Distribution at the University of Arizona’s Campus Mall.
Volunteers assist drivers at COVID 19 Vaccine Point of Distribution at the University of Arizona’s Campus Mall. Chris Richards/University of Arizona


In the United States, more people have been at least partially vaccinated against SARS-CoV-2 – the virus that causes COVID-19 – than have contracted it. To date, over 27.4 million confirmed cases of COVID-19 have been reported, while 38.3 million people have received at least one dose of the vaccine, according to the Centers for Disease Control and Prevention.

In Arizona, nearly 800,000 COVID-19 cases have been reported to date, while more than 840,000 people have received at least one shot.

Yet, this is just the beginning of the battle. The number of confirmed cases per day is falling nationally, and the trend should continue as the vaccine reaches more people. But many scientists agree that for the population to reach herd immunity, at least 70% of people should receive both doses of the currently available Pfizer or Moderna vaccines.


Deepta Bhattacharya
Deepta Bhattacharya

As more people become eligible for vaccination and variants continue to spread, more questions arise. So, UArizona News again spoke with Deepta Bhattacharya, an associate professor in the Department of Immunobiology and a member of the university's BIO5 Institute who studies immune responses to infections and vaccines.

Bhattacharya's latest insights come on the heels of UArizona announcing that it will become a high-capacity state vaccination site this week. Appointments are required and can be made through the Arizona Department of Health Services website by those eligible in Priority Phase 1B.

Q: Why do many people feel bad after vaccination? What should we expect to feel after the first dose and second dose? How should we take care of the symptoms? 

A: The vaccines are designed to induce some inflammation so that your body triggers an immune response. This, in turn, can make you feel badly after the shots. For most people, the first shot doesn't do much – maybe a sore arm. After the second shot, many people feel worse, with a headache, fatigue or low-grade fever. This usually goes away within a day or two, and it is all a normal part of the process. You can take ibuprofen or Tylenol if you really don't feel great, but there is some experimental data that suggests these might inhibit your immune response.

Q: Why do people have such different reactions? It's often said that if you have symptoms, it means the vaccine is working. If you don't have symptoms, it's still working, right?

A: Yes, even if you don't have symptoms, the vaccine is still working. Most people will feel something. We don't really know why a minority of people avoid these symptoms, but as far as we can tell, it doesn't make much difference in the quality of your immune response. The University of Arizona does offer an antibody test if people would like to confirm that they have mounted an immune response.

Q: Can and should your behavior change after receiving the first and second doses?

A: After the first shot, definitely not. Protection doesn't kick in until about two weeks after the immunization, and it is not yet maximal if you take just the first shot. About a week or two after the second shot is when protection reaches its peak levels. As for behavior after that, well, that is complicated. Certainly, small gatherings with others who are all fully vaccinated becomes of much lower risk than it had been, and it is something that people can look forward to after they have gotten the vaccine. On the other hand, you will hear of people getting infected and sick even after the vaccine, especially if community transmission is high. They are excellent vaccines, but there is no such thing as perfection in this world. But as more and more people get vaccinated, and community transmission falls, the chances of getting infected and sick will start to drop by a lot. As that happens, the remaining risks will continue to decline, and activities we have been holding off from will become safer.

Q: What do we know about transmission after vaccination?

A: We are pretty confident it will decrease, probably by a lot, but can't quite put a number on it yet. Preliminary studies in Moderna's trial and from Pfizer/BioNTech's real-world data in Israel have made it clear that the number of infections are decreasing by a lot after vaccination. So, the vaccines are not just reducing symptoms; they are also reducing infections. If you are not infected, you obviously can't transmit. What we don't yet know is in the small fraction of vaccinated people who do get breakthrough infections, how likely are they to transmit to others? Based on the immunology of these vaccines and the biology of the virus, the chances of onward transmission are likely reduced. We just need some more contact tracing studies to put a number on it.

Q: If transmission can still occur after getting the vaccine, then how does it help us achieve herd immunity?

A: All indications are that the vaccine will reduce transmission, probably by substantial amounts. But I do want to make the distinction between "reduce" and "eliminate." I can say with 100% confidence that the vaccines will not eliminate 100% of transmission. People with breakthrough infections almost certainly can transmit to others, although the likelihood of this happening will likely be less than by unvaccinated people. This is one of the reasons we are asking people to hang on and be careful for just a little while longer while as the population gets vaccinated. As that happens, community transmission will drop, as will the chances of getting infected in the first place.

Q: If someone has already contracted and recovered from COVID-19, should they still get vaccinated?

A: There are no safety concerns, but there are some things to think about. First, there is now a lot of data showing that the risk of re-infection is pretty low after you have recovered, at least for six to eight months. As vaccine demand is still far greater than supply, you may want to consider waiting a bit and giving others who are at greater risk a chance to get immunized. Second, there is emerging data that one shot is generally sufficient to max out the immune response in people who have recovered. If people who have recovered from COVID relatively recently factor these things in, it may allow for more efficient usage of our vaccine supply.

Q: How well do the current vaccines protect us against new variants of the virus? Is one vaccine more effective than the other?

A: The vaccines seem to remain effective against the variant called B.1.1.7, which was first identified in the U.K. and is growing in prevalence here. Antibodies elicited by the vaccine stick a little bit worse to two other variants, called B.1.351 and P1, which were first identified in South Africa and Brazil, respectively. We are not exactly sure how much vaccine efficacy will be impacted yet by these variants, but I can guarantee that it won't fall to zero against either one. So far, we have some data from the Novavax and Johnson and Johnson (vaccine candidate) trials, and in both cases, the impact on vaccine efficacy is only partial. Both are still fully effective in preventing severe disease and keeping people out of the hospital. So far, neither the B.1.351 nor the P1 variants are widespread here, and it would really behoove us to do what we can with distancing, vaccinating, et cetera to keep them from taking hold.

Q: Should we continue to get tested after being vaccinated?

A: If you feel symptoms or had an encounter with someone with COVID, yes, you should get tested.

Q: No one can predict the future, but what do you think the next six months to a year look like in terms of some of the aspects of our lives that have been impacted most, such as traveling and gathering?  

A: I am very hopeful that many activities, like travel to see family and friends, will be much safer to do by the summer. I think that community transmission will likely be a lot lower by then, and even though there probably won't yet be a vaccine for children, most activities will still be much safer. We just need to get people immunized quickly.

Extra info

For the latest on the University of Arizona response to the novel coronavirus, visit the university's COVID-19 webpage.

For UANews coverage of COVID-19, visit


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