Will a vaccine stop the pandemic?

In order to stop transmission, a vaccine would need to provide sterilizing immunity. This means that the vaccine would completely prevent infection by the virus. Isn’t that what vaccines are supposed to do? Ideally, yes, but in the real world, this isn’t always the case.

Location matters! All of the vaccines that are currently being tested in people are delivered by injection. A shot in the arm triggers an immune response in the blood and lymph system, but not necessarily in the nose and throat where the virus initially replicates. This type of response will protect against severe infection in the lungs, but may still permit virus replication and spread from the nose and throat. This is similar to the flu shot: you might still get cold-like symptoms from an influenza virus infection after getting the vaccine, but the vaccine protects your lungs from getting severe influenza. Researchers are currently developing nasal vaccines that might provide sterilizing immunity, but these won’t likely be the first vaccines available.

If infection doesn’t induce sterilizing immunity, it is unlikely that the vaccine will! We know that infection by seasonal coronaviruses, those that cause common colds, does not result in long-lived protective immunity. Human volunteers that were given these mild coronaviruses were susceptible to re-infection by the same virus after 1 year. This is also true for other respiratory viral infections. We repeatedly get infected by respiratory syncytial virus (RSV) through-out life. The first infection with RSV is the most severe, but we continue to have mild RSV infections that resemble the common cold. In this case, re-infection isn’t due to the virus changing, it is actually genetically stable. Our immune system just doesn’t induce long-term protective immunity against the virus in the nose and throat. There have been reported cases of people being re-infected by SARS-CoV-2 (the virus that causes COVID-19). This suggests that sterilizing immunity may not be induced by natural infection, at least in some people.

Not everyone will get the vaccine at the same time! Even if a vaccine that stops transmission becomes available, it won’t be given to everyone immediately. The National Academy of Medicine has proposed a phased approach to vaccine allocation, that starts with health workers and people with significantly higher risk for severe disease. Over the summer, the age demographics of COVID-19 shifted to younger adults, when the incidence of infection was highest in the 20-29 year age group. The increase in positive cases in the younger adults was followed by an increase in cases in older adults, suggesting that cases in the younger age group contributes to transmission within the community. Despite their contribution to viral transmission, young adults would not be vaccinated until phase 3 of the plan, which is the second-to-last phase. Vaccine testing also has not started in pediatric populations and would need to be completed before children could receive the vaccine.

Not everyone will get the vaccine at all! With the speed of vaccine development and testing and the involvement of politics in the process, many people are concerned that a vaccine will be licensed before it is deemed safe and/or effective. Based on recent polls, public trust in a COVID-19 vaccine has declined. Based on the infectiousness of the virus, a significant proportion of the population would need to be vaccinated to stop viral transmission. No matter how effective the vaccine is, if people refuse vaccination the virus will continue to spread.

How does this knowledge inform my decisions about vaccination? As long as the government pressure to approve a vaccine does not interfere with the roles of regulatory groups such as the Federal Drug Administration and the Data and Safety Monitoring Board, I will get in line for my COVID shot. However, unless it has been proven to effectively stop viral transmission, I will continue to wear my mask and social distance after I have received my vaccine.

To view a recent colloquium on this topic: https://www.youtube.com/watch?v=YzQaDPLsshM&feature=emb_logo