A person's arm is shown getting the vaccine
March 3, 2021



Author: Iqbal Pittalwala
March 3, 2021

Recently, experts at the University of California shared their views on whether COVID-19 is here to stay. They now answer more questions related to COVID-19 vaccines, face masks, antibodies, herd immunity, and coronavirus variants.

Dr. David Lo, distinguished professor of biomedical sciences, School of Medicine:

Can people who got the vaccine be carriers?

The vaccine against COVID is intended to produce an immune response against the virus SARS-CoV-2, which causes disease as it tricks the immune system into thinking it is responding to an actual infection. Ideally, the best vaccine induces a stronger immune response than an actual infection. So far, the evidence is that the available vaccines against COVID-19 actually do a better job at inducing immunity than an actual infection.
But it should be clear that while the vaccines are quite good at producing an immune response, some people who have had a full vaccine course, if exposed to the virus, might still get a COVID-19 infection. The vaccination will still prevent you from getting very sick and pretty much prevent you from dying of the infection — a sound argument for getting vaccinated. In addition, for those who got vaccinated but still got infected, they are also far less likely to spread the infection, and so are less likely to be “carriers” of infection. However, you still don’t want to take too many chances that might have you pass the infection along to somebody you care about, so you should still wear a mask. Since up to half the people with infections have no symptoms at all, it is best to be cautious.

How vulnerable are unvaccinated people who have to be near or live with the vaccinated? 

Some people for one reason or another might not be able to get vaccinated; it could be due to an allergy to the vaccine, or they have an immune deficiency that prevents them from responding to the vaccine, or some other reason. Some of these folks might even have a greater risk of having severe disease or death if they do end up getting infected. What can they do? It is, of course, a great idea to have others close to you get vaccinated, to reduce risk of getting the disease from them. We know vaccination helps protect the vaccinated, and they are far less able to spread disease if they do get infected.

We don’t yet know whether the risk is completely eliminated, and many people who are infected might have no symptoms at all. So if you have not been vaccinated, and you do not want to risk getting infected, it might be safe for you to still take some care even near people who have been vaccinated. With basic steps such as wearing masks, hand washing, and distancing measures, we can all reduce the chance of spread.

How long should a person wait to get the vaccine if they already had COVID-19?

The recommendation is that you should still get vaccinated even if you have had the COVID-19 infection. There are some cases where people have been reinfected because the immune response was not enough to prevent reinfection. The immunity generated by vaccination is better than immunity from an actual infection because it is designed to induce a stronger and longer-lasting immunity. So it is a good idea to get the vaccine even if you have been infected. There is no reason to wait a long time after infection before getting vaccinated if it is available.

Richard M. Carpiano, professor, School of Public Policy and Department of Sociology:

How could people who refuse a COVID-19 vaccine undermine efforts to establish herd immunity to the coronavirus?

When it comes to being vaccinated from the COVID-19 vaccine, we now have three vaccine options. Each of these have been found in clinical trials to greatly reduce one’s risk of getting COVID-19, but like any vaccine, none of these can provide 100% protection. That’s why it is so important for as many people as possible to get vaccinated — even if they have already had COVID-19. More people vaccinated means fewer opportunities for the coronavirus to spread. This protects not only those who cannot be vaccinated but gives those who are vaccinated even further protection. This is called herd immunity, but given how it helps us protect each other, it is sometimes referred to as “community immunity.” The specific percentage of vaccination coverage in a population needed for herd immunity differs by disease. For COVID-19, it is still unknown, but experts estimate it being somewhere in the range between 70%-90% coverage. 

The three COVID-19 vaccines authorized for use in the U.S. were found in their respective clinical trials to be incredibly safe. Furthermore, close monitoring of the millions of doses of the Moderna and Pfizer vaccines already distributed across the country provide even greater evidence of their high level of safety. Nevertheless, there will always be people who refuse a vaccine — for COVID-19 or other diseases. When it comes to protection from infectious diseases, we are all dependent upon each other for protection. 

It is a common misconception among people who refuse other vaccines that they can simply rely on the protection provided by everyone else getting vaccinated. But any “I’m just one person, what harm would it cause?” rationale still impacts the larger group because individuals often do not think about the consequences of other people making the very same decision as them. As such, this personal misconception becomes a collective problem and hampers our ability to reach the threshold needed for herd immunity in the local communities where we spend our daily routines.  

More concerning though are people who refuse to get vaccinated — often based on claims of personal freedom — but then engage in efforts to spread disinformation or conspiracy theories about the vaccines and/or the risk of the disease the vaccine aims to prevent. COVID-19 has been no exception to this phenomenon. Already we have seen false information about adverse events from COVID-19 vaccines. Such dangerous activities stoke fear and confusion and impact people’s decision-making process for protecting themselves, their loved ones, and their communities. In short, it puts people at risk and ultimately prolongs this pandemic.

As the COVID-19 vaccination rollout progresses in the coming months, it is important to keep in mind that state and national vaccination statistics only tell part of the herd immunity story. Since COVID-19 is a disease that people spread to others with whom they come into contact through everyday situations, having a high percentage of people in your local community vaccinated is key. Thus, even if county-, state-, and national-level vaccination statistics look promising, they can mask pockets of low vaccination coverage in local areas — counties, towns, neighborhoods — where people conduct most of their activities. 

Adam Godzik, professor of biomedical sciences, School of Medicine:

Can the coronavirus strain now dominant in California swap mutations with other threatening strains?

There are two major mechanisms of how viruses evolve — spontaneous mutations/genetic changes and recombination. Both contribute to the evolution/spread of the variants; we just don’t know to what extent. For instance, the “California” variant recently acquired the D69-70 mutation found previously in the South African strain; and the “U.K.” variant acquired the E484K mutation that is identical to a mutation in the South African and Brazilian strains; but it is unclear how these occurred. RNA viruses, such as influenza, often undergo recombination. The bottom line is that we may not know how, but the variants are evolving and acquiring new, potentially dangerous, features. The big question is: How would the virus behave in a partially vaccinated population or a population with a borderline herd immunity? It is possible it could evolve to escape the immune response of the vaccinated people. On the other hand, we could, hopefully, be able to squash the epidemic before the variants take hold. We are in a sort of a race: Will we manage to achieve herd immunity before the new variants expand or not?

Brandon J. Brown, associate professor and epidemiologist, School of Medicine:

When after vaccination can we stop wearing masks?

After you are vaccinated, you have to continue wearing a face covering and engage in physical distancing until everyone else has had the chance to get the vaccine. You may be able to spread the virus to others even after you are vaccinated and even if you don’t get sick. We need to get as many people vaccinated as possible, especially with the emergence of variants.

Karine G. Le Roch, director, Center for Infectious Disease and Vector Control:

Can antibodies be passed from mother to child during breastfeeding?

A recent study reported that milk samples collected from 18 women following COVID-19 diagnosis did not contain SARS-CoV-2 RNA. Most importantly, the team of researchers were able to detect in those milk samples neutralizing antibodies against SARS-CoV-2. While these results will need to be further validated in larger cohorts, they are highly encouraging and support breastfeeding during mild-to-moderate maternal COVID-19 illness. This study provides new clarity on guidance for breastfeeding as milk will most likely offer protection to infants.  Another major question that still remains to be answered is the impact of the COVID-19 vaccine on breast milk. Presently, we don’t have enough data to confirm that antibodies generated after vaccination will provide the same type of protection.

Dr. Brenda Ross-Shelton, assistant clinical professor, School of Medicine:

Is the vaccine recommended for women who want to get pregnant? Should women wait a certain amount of time to get pregnant after receiving the vaccine?

Complications among COVID-19-infected pregnant patients can be severe. Consequently, the COVID-19 vaccine is recommended and can be safely administered at all trimesters of pregnancy. There have been no studies to demonstrate an associated increased risk of fetal anomalies or poor pregnancy outcome. For patients who are considering pregnancy, vaccination prior to conception is reasonable. There is no prescribed waiting period for attempting conception post vaccination.

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