Recent public messaging harps on the idea that people can still become infected and transmit COVID-19 after they get vaccinated. While that is a risk, it’s an extremely low risk, and not worth the negative consequence: it’s stopping people from getting vaccinated.
People are using the idea that others can spread the virus after being vaccinated to claim that the vaccine does not work and therefore should not be taken. I have spoken with people who have done just that.
Vaccine trials measure how many people get infected after vaccination. Take for example the Moderna vaccine trial, published in the New England Journal of Medicine beginning in November with follow-up publications extending through February. In that trial they randomized 15,210 people to the vaccine and 15,210 people to placebo. Of those who got the placebo, 185 developed COVID-19. Therefore, 1.2% got COVID-19. Thirty of those became very ill. Of those who got the vaccine, 11 developed COVID-19. None of them got very ill. Therefore, 0.07% got COVID-19. So, the vaccine was effective: it prevented illness and it prevented serious illness.
The efficacy of the vaccine is quoted as 94%. That figure is arrived at by dividing 0.07 by 1.2, which equals 6%. Subtracting that from 100% equals 94%. This math can be worked in different ways but the bottom line is that 11 of 15,210 became mildly ill with COVID-19 after the vaccine. Those 11 could spread the illness. But 11 out of 15,210 is a very low number. But that is 22 out of about 30,000 and 44 out of about 60,000. So it is true that some might spread COVID-19 after the vaccination but it is also true that the risk of that is very low.
We also know that the spread of COVID-19 is greater when patients are sicker, when they are sneezing and coughing, and have evidence of a stronger infection. Those with mild or asymptomatic disease are less likely to spread the illness. Therefore, by reducing symptoms, that vaccine reduces viral spread, though perhaps not completely.
The COVID-19 vaccine trials did not directly evaluate the possibility of spread after vaccination. That is difficult to do. Do you follow those 11 to see if they come in contact with anyone and spread it? If they don’t do you conclude that it can’t be spread or do you conclude that they didn’t come in contact with vulnerable people under vulnerable conditions? Determining the risk of spread probably can’t be done in a realistic manner.
In the Moderna trial, about 100 patients had positive viral RNA swabs at the beginning of the trial. They were not symptomatic. Therefore, they were asymptomatic carriers. After the first dose of the vaccine, these participants were tested for viral RNA at the time of the second vaccine dose. Of the group that got the vaccine, 15 still had positive swabs. Therefore, after the first vaccine the asymptomatic carrier rate went down. Though the trial did not directly test for prevention of asymptomatic infection, it offers evidence along those lines. The asymptomatic carrier rate went down and it does not appear that new asymptomatic carriers were identified. However, the study was not designed to definitively answer this question about prevention of asymptomatic carriers.
Another way to approach this issue of whether the vaccine prevents spread is to consider what happens with other vaccines. When we give the flu vaccine do we find that those who get the vaccine contract the flu and pass it on to others at a clinically significant rate? The answer is no. Can it happen? The answer is yes. The flu vaccine, like the COVID-19 vaccine, is not perfect. But it is highly effective. The same holds for the smallpox vaccine (smallpox is now obliterated from the planet by vaccination), the polio vaccine, and others. Even when vaccines are not perfect they can be highly effective. Therefore, to harp on the rare possibility of spreading COVID-19 after vaccination is to focus on what is unlikely to happen rather than to focus on what is likely to happen — that it will work very well.
This messaging is in part driven by the fact that we live in a media age that needs talking points. To say that the vaccine is effective is not a dramatic talking point. But as soon as you suggest that it may not work for spread of the illness, people prick up their ears.
Experts fall prey to the same psychology. Such talking points allow them to go on television and pontificate. Some experts even like to make things more complicated than they need to be, and some have great fears about being seen as wrong. One way to avoid that is to equivocate, to harp on what we don’t know because to be too definitive is to run the risk of someone finding one example of spread and then say, “Look, he was wrong.” Which then escalates into, “He doesn’t know what he is talking about.” Which escalates into, “He is an idiot.” Which escalates into “experts don’t know what they are talking about.” This happened with Dr. Fauci: he made a few minor mistakes and that prompted some to go after him in this manner. That underhanded approach was also used in politics over the last four years.
A lot of things might happen. But it is not smart to focus on what might be the case rather than on what is likely to be the case. When you drive your car, you might get into an accident. But no reasonable person uses that possibility to not drive. But when it comes to the practice of medicine, some seem to believe that even the slightest risk needs to be emphasized. This approach can lead to harmful consequences.
Instead, we need to be more explicit about the data and use messaging that encourages people to get vaccinated.
It is very unlikely that two weeks after a person receives the second COVID-19 vaccine that he or she will spread the virus. Nevertheless, it is a rare possibility. There were those 11 people out of 15,210 who developed COVID-19. Therefore, wearing masks after getting the vaccine is justified. But what is not justified is spreading the word that spread of the virus after vaccination is a serious threat. What is not justified is giving people a talking point which is used to say that the vaccine does not work.
It does. It is effective. It is our only best hope for ending the pandemic.
W. Robert Graham, MD, completed medical school and residency at UTHSC-Dallas (Parkland Hospital) and served as chief resident. He received a National Institutes of Health fellowship at the Salk Institute for oncogene research in 1985, and was a professor of medicine at Baylor College of Medicine from 1998 through 2016. In retirement, he enjoys writing and ranching.
Last Updated February 22, 2021