This post will attempt to answer the following question:
- What is known about the Moderna and Pfizer vaccines?
- Can you still get COVID-19 and be contagious after you are vaccinated?
- How can we find out if the vaccine prevents viral transmission?
It’s a normal part of human nature to adapt to whatever situation we find ourselves in. We get used to both the good and the bad if given enough time. It’s just how we’re designed and is essential for our well being. During this pandemic, however, it has become a sign of how bad things have become. In the United States, where case numbers are astronomically higher than just about anywhere else in the world (USA! USA!), we’ve been hovering near 200,000 new cases with a few thousand deaths every day for a couple of months now. We have become so numb to these numbers that we don’t flinch when we hear them. When the case rates drop to 150,000 we feel as if things are going really. Remember when 30,000 was a lot? Neither does anyone else.The adaptation and subsequent lack of shock at the numbers combined with pandemic fatigue, anger, and even denial fuels the desperation for an end. For better or worse, that end only comes when enough of us are protected through vaccination. Until that happens, there will be a transition period. It will be a period where a lot of people are vaccinated but not quite enough to prevent devastating surges like many parts of the country have seen over the past 2 months. How long this period will last and what it will look like remain to be seen. There is no negotiating with this virus.
Many are justifiably excited to get their vaccine, dreaming of mask-free social gatherings and carefree hugs but, as with everything else in this pandemic, people are getting a bit ahead of themselves. It’s very important to understand what is known and what is not known about the Moderna and Pfizer vaccines before we throw away our masks and have a party..
All that is known about these vaccines is that, when they are given to a large population of people, far fewer people get symptomatic COVID-19 infection. That’s it.
The trials were conducted in a way where >20,000 individuals were either given the vaccine or a placebo and watched to see how many people developed a symptomatic infection. To round up for easy math, in the Pfizer study there were about 200 people in the placebo group and 10 in the vaccine group who had a symptomatic infection. We make the assumption that the excess 190 people in the vaccine group would have contracted a symptomatic infection if they were not vaccinated.
Notice that this study did not measure how many actual infections there were. To do that, they would have had to test all 40,000 individuals at regular intervals which was not feasible. This means it is possible that those 190 people who did not get a symptomatic infection got an asymptomatic infection rendering them still contagious.
It is not a crazy thought to think that the COVID vaccine might prevent severe infection but still allow for people to be contagious. The vaccine for hepatitis B, rotavirus, pertussis, and one of the pneumonia vaccines decrease, but do not prevent, transmission. This would not be an unprecedented occurrence.
There are many reasons why this could be the case. It could be that the vaccine drops viral levels enough to prevent severe infections but doesn’t knock it down enough to prevent mild but still contagious ones. It could also be that the vaccine only stimulates production of the antibody IgG which circulates inside the body. The main antibody that protects from invasion into mucosal surfaces like the respiratory and GI tract is IgA. A Many respiratory viruses can develop a strong enough immune response through an injection (e.g. measles) to stimulate IgA production but not all. Blocking IgA is especially important for respiratory viruses.
As you can imagine, if the vaccine doesn’t prevent transmission, this could create a very dangerous situation. Imagine you have a population of several million vaccinated individuals who think they are protected completely and take no precautions to prevent spread. Many of them could get an asymptomatic infection and spread the the virus widely. This could be a disaster for all the people who are not yet vaccinated.
So what now?
One way to get the answer on transmission is to do human challenge trials. These are studies where people are given the vaccine. They then have the virus squirted into their nose and get covid testing at regular intervals for a couple weeks. This form of research could answer the questions quickly without great expense since it would require fewer test subjects for statistical reasons. The problem with the vaccine trials is the relatively low case rates (e.g. 200 per 20,000). This means you have to study tens of thousands to get enough cases to be sure your findings aren’t due to chance. If you can guarantee that every subject is exposed you need far fewer test subjects. Volunteering to be exposed to the coronavirus sounds crazy, but sacrificing your own well being to benefit others is not a new idea; firefighters, police officers, and hospital workers do it every day. They would also only study young and low risk people so the chances of severe infection are very very low. Thousands have already volunteered.
A second way is to follow a large group of college students or perhaps soldiers who share living quarters in large numbers. Dorms and barracks are an environment perfect for spreading all manner of infectious disease. You would give half the students the vaccine and half a placebo. The virus would spread as it naturally does in these communities, but the participants would undergo regular and frequent viral testing. You could compare transmission in the two groups. This would require more subjects and take longer because you can’t control the numbers of infections.
If we cannot get answers on transmission through the above methods we will be stuck with epidemiology. What will need to be done is to track the case numbers, hospitalizations, and deaths along with vaccination numbers. If these numbers rapidly go down in concert with rising vaccination rates it will be a good sign that we can ease restrictions, at least for those who are vaccinated.
Simulations have been run to estimate what it would take to end the pandemic completely have found that if a vaccine protects 80% of those immunized and 75% of the population is vaccinated, it could largely end an epidemic without other measures such as social distancing. If the vaccine only prevents severe disease but not transmission additional public health measures may still be necessary.
In other words we still need to wear masks until enough people are vaccinated and we know if disease transmission is prevented. This will likely not be a switch that turns the pandemic off. The most likely scenario is that restrictions will be eased incrementally as more people are vaccinated and the numbers come down. If research clearly shows the vaccine prevents transmission in the interim the restrictions will come off faster.
For now, I’ve got to go help a woman say goodbye to her mother who is dying from COVID. She has to sit outside the room and look through the glass for their last moments together. It has been such a long year but, sadly, like the rest of us, I have adapted and these moments are no longer strange to me.