There have been some scary headlines lately when it comes to vaccinating Covid-19:
The thing is, none of these headlines should be surprising, or so scary.
According to clinical trial data, the Pfizer / BioNtech vaccine is 95 percent effective in preventing Covid-19 disease. The Modern vaccine is 94 percent. The Johnson & Johnson single-dose vaccine is between 66 and 72 percent effective (and higher for preventing serious illness). What you will notice in all the figures: None is 100 percent effective in preventing the disease.
This should be clear from the clinical trial data, but it is surprising: it is possible to become ill with Covid-19 – or possibly carry the virus asymptomatically – after being completely vaccinated with any of these vaccines. These are called breakthrough infections. “This is what we expect to see: some cases among vaccinated people,” says Natalie Dean, a biostatistician at the University of Florida.
It is also not surprising to see some (extremely rare) cases of hospitalizations and serious illnesses among people who have been vaccinated. This may seem even more bizarre, as tens of thousands of people’s clinical trials reported that these vaccines were 100 percent effective in preventing hospitalizations.
But “nothing is 100 percent,” Dean says. “If you start vaccinating millions of people, even things that are relatively rare will come up.” The real culprit behind the breakthrough infections is not the vaccines – it’s the fact that this pandemic is still raging in many communities.
But why would a vaccinated person ever get sick?
So far, I have talked about the effectiveness of the vaccine in terms of disease prevention. There is also the demand for the vaccines that prevent infection. It is slightly different: disease shows symptoms; infection is merely positive for the virus (perhaps asymptomatic). On this, it seems so far that the vaccines are also good for preventing infection. A recent study by the Centers for Disease Control and Prevention of 3,950 health workers found that the mRNA vaccines (Moderna and Pfizer / BioNtech) were 90 percent effective in preventing any infection.
There is less actual data on the Johnson & Johnson vaccine, but the CDC writes that early evidence suggests that it ‘may provide protection against asymptomatic infection’.
That is, most vaccines will prevent Covid-19 infection from taking hold in the body. This is amazing! And that’s why these vaccines are our best chance to end the pandemic. But some of the time, it will not prevent infection, nor symptoms.
Why? Think of the immunity that the vaccine provides as a dam, says Erin Bromage, an immunologist at UMass Dartmouth.
“No dam, for example, is 100 percent effective,” he says. ‘They are designed to handle storms of 20 years and 50 years. But they are overwhelmed when a storm of 100 years comes. ”
But there are circumstances in which infection can overwhelm this immunological dam.
The exact reasons are not exactly known. Some circumstances that lead to a breakthrough can be predicted, but others just may not be, Bromage says. “You do not know who it will be.”
Just as humans have different immune responses, and the severity of diseases varies when they contract the virus, humans have different (but less so) immune responses to vaccines. (It’s also like some people get a lot of side effects from the vaccine, and others do not. Everyone’s body reacts just a little differently.)
So, based on what we know so far, a large portion of those who will experience breakthrough infections are just hard to predict.
But there are also some things that scientists suspect could make it more likely.
This could be the amount of virus someone is exposed to. Like how a dam will be broken when a major flood rushes in, immune protection against vaccines can be overwhelmed if someone is exposed to a lot of viral particles (perhaps by working with someone who is sick with Covid-19, or by working in ‘ a healthcare facility that handles Covid-19 patents.
Other times, ‘the foundation on which the dam was built is not strong enough’, says Bromage, who caused the dam to break. A person with an immune system may be at risk for a breakthrough infection. “We know, for example, that people with HIV have lower levels of protection,” says Dean. “It could reflect something about the immune response.”
Age can also play a role. There is evidence from Israel that the Pfizer / BioNTech vaccine may be at least slightly less effective for people over 80. Although Dean says about this question about efficacy and age, ‘We do not have much data. ”
And then there are more common things in our lives that can temporarily make us more susceptible to infection. Sleep quality can play a role in the strength of the immune system. Tension can too.
It is also the case that the vaccines only take a while to reach full effectiveness. “The prudence is to be protected for a maximum of 14 days or a period after the second dose,” says Dean. Thus, you are more likely to see a breakthrough infection early after being vaccinated, or when you have only received one dose of two-dose vaccine.
Breakthrough infections are less serious, and possibly less transmissible – even with new variants
This is the good news: there are many reasons to believe that when these breakthrough infections occur, they are not as bad as when the person was not vaccinated. First, we know this from the clinical trial data of tens of thousands of people: Of all three approved vaccines, there was 100 percent efficacy in preventing deaths and hospitalizations. (Again, as Dean says, nothing is 100 percent. But it’s pretty damn good.)
Data collected after the trials, in actual circumstances, also contribute to this. Recently, a 5,000-patient study from Israel compared cases of breakthrough infections (after vaccination) with infections that occurred among unvaccinated people. Simply put, the study found that those who had breakthrough infections also had smaller amounts of viruses. This particular study does not contain information on the severity of the symptoms. But lower virus burden was correlated with a lower severity of the disease; it also lowers the risk of transmission to other people.
The Israeli study only evaluated people who took the Pfizer / BioNtech vaccine (it is virtually the only vaccine offered in Israel). But it is obvious to expect a similar pattern of the Moderna vaccine and perhaps the Johnson & Johnson vaccine. The results of the study ‘should encourage people to be vaccinated’, says Idan Yelin, a biology researcher at the Technion-Israel Institute of Technology, who co-authored the analysis. ‘When you get vaccinated, you’re doing something good for yourself, but also doing good for people around you. That should be the message. ”
But what about variants? Another study yet to be published, also from Israel, asked this question. After one dose of Pfizer / BioNtech vaccine, humans were found to be slightly more susceptible to infection with the B.1.1.7 variant (first discovered in the UK and now the dominant strain in the US) and the B .1351 variant (first discovered in South Africa) as the original SARS-CoV-2 virus. After the full two doses, the vaccines seemed to protect people almost completely against B.1.1.7, but they were slightly less – but still quite – effective against B.1351.
Interestingly, the authors of the study note that, although they see that the B.1351 variant is slightly more likely to break through, there is just not much B.1351 distributed in Israel. ‘We think that this reduced efficiency will only occur in a short time, and that the SA variant [B.1351] does not spread efficiently, ”tweeted Adi Stern, the senior writer at the newspaper.
The fact that there is not much spread of B.1351 in Israel indicates ‘that these breakthrough infections are a dead end’, said virologist Angela Rasmussen. explained on Twitter. Although it may be more difficult to spread in Israel compared to other countries: to date, Israel has vaccinated more than 60 percent of its population.
Other vaccines may be less protective against various breakthroughs, especially those produced by AstraZeneca: they are perhaps only 70 percent effective against the B.1.1.7 variant and only 10 percent effective against B.1351.
But the core is still the same: the best protection against infections, against variants or not, is completely vaccinated.
The number of breakthrough infections depends on the amount of virus circulating
If a vaccine is 95 percent effective, it means that a person who has been vaccinated is 95 percent less likely to get sick than another person if he or she is exposed to the virus. The most important part of the last sentence: when exposed to the virus.
Breakthrough infections occur in a small proportion of those who are vaccinated, but the number of breakthrough infections that accumulate depends on how many viruses are spreading in the community.
“The risk of these breakthroughs actually reflects how much transmission there is in the community,” Dean says. Vaccinations against measles are also not completely effective (it is about 97 percent effective). But we do not see many cases of measles under the vaccine, because it is very rarely exposed to the measles.
Simply put, the more cases there are, the more breakthrough infections there will be. The answer to the problem of breakthrough infections is therefore only to vaccinate more people (to further reduce the transmission), to continue to wear masks and to maintain distance between groups of people with mixed vaccination status. (Read the CDC’s complete vaccination guidelines here.)
“Until we experience these daily occurrences, we are going to look at these rare events,” Bromage says.