The authorized coronavirus vaccines are exceptionally effective but not 100% so. No vaccine provides one hundred percent protection to all people. As a result, breakthrough infections are to be expected. Are you at risk?
The concept of breakthrough is when a fully vaccinated person later gets an infection. It is important to remember that not everyone responds to vaccines equally. The flu vaccine is a good example. Older people, for example, usually do not develop as great an immunity as do younger people. That is why in recent years the flu vaccine is given in a higher dose to those over 65. Still, the boosted vaccine does not prevent all flu infections. My wife and I learned from experience. A few years ago, a couple of months after getting the flu vaccine, we were at our favorite sushi restaurant and sitting at the sushi bar. The owner came by and said to us that they had a lot of their chefs developing what seemed to be the flu and she had sent them home. But there we were sitting directly across from where the chefs were working. A few days later we both woke up and knew exactly what we had.
The influenza vaccine, in a good year, tends to be about sixty percent effective. Meaning that about forty percent of people can still get infected if exposed even though they have been vaccinated. Fortunately, those who do get infected usually develop a less serious infection. That is still good. And even though the vaccine not 100% effective, it is still considered very valuable. It not only prevents infection in at last half of exposed persons but it also limits the spread so that many fewer get exposed.
In considering breakthrough infections, remember that the person who has been vaccinated almost certainly has some level of immunity. Therefore, the breakthrough infection is likely to be mild or even asymptomatic.
The COVID-19 vaccines are very effective. They prevent most people from getting a mild or moderate infection and they almost always prevent the development of an infection severe enough to lead to hospitalization and death. Many experts would say that these vaccines are way more effective than what was hoped for or even dreamed of nine months ago as the start of the large phase III trials.
To date, almost eighty million Americans have been fully vaccinated and less than ten thousand breakthroughs have been detected. Of course, that is so far. More will occur. If we look back to the original clinical trials that were presented to the Food and Drug Administration, the Pfizer-BioNTech vaccine had a ninety-five percent efficacy rate, the Moderna ninety-four percent, and the Johnson & Johnson sixty-six percent. AstraZeneca and Novavax will probably be presenting their data in the near future. Those vaccines will likely have very good efficacy rates as well.
Pfizer has now updated its information at six months. Remember, the data presented to the FDA in December had at least two months of information but now, at six months, the Pfizer vaccine is still doing well at ninety-one percent. To look back at the specifics, at two months the Pfizer large phase III clinical trials of some 44,000 volunteers found that, beginning two weeks after the second shot, in the placebo group there were 162 coronavirus infections whereas in the vaccinated group there were eight. Now at six months, the numbers are 697 in the placebo volunteers and fifty in the vaccinated group. So, there were some vaccinated individuals who developed infection, called a breakthrough infection, during those clinical trials.
What is your risk of a breakthrough? Low but real.
It is important to understand risk calculations. A 95% vaccine efficacy does not mean that five of every 100 vaccinated people will become infected. Remember that those Phase 3 clinical trials enrolled many thousands of individuals. In the Pfizer trial, for example, some 22,000 got the placebo and an equal number got the vaccine. At two months, 8 of the vaccinated volunteers developed symptomatic infection and by six months 50 have become infected, none with a need for hospitalization and no one died.
The first question to ask is, in this group, what was the risk of becoming infected? For the placebo patients in the Pfizer trial, it was about 0.8%. In other words, not all that many volunteers were exposed and hence were liable to become infected. Maybe, since they were volunteering in a study, they were also very careful to follow the guidelines for avoiding infection like masking and social distancing. But for those who were exposed. The vaccinated individuals had a very much lower (0.04%) but not zero risk of infection than did the placebo volunteers, hence the observed breakthrough infections.
The second question is to assess your own risk. Your risk would likely be higher if you are taking a medication that inhibits your immune response. Your risk might be somewhat higher if you frequent crowded bars, areas where the air exchange is limited or if you and others around you do not wear a mask or social distance. You might be living in an area where the infection is rampant versus someone living in an area where relatively few people are becoming infected. The risk is obviously going to be higher in the former than in the latter.
What are the numbers?
So far in the United States, most of the breakthrough infections have been mild but there have been a serious ones. In Washington state, as of March 30, after vaccinating 1.2 million individuals, there were 102 breakthrough infections or a risk of developing a breakthrough infection of 0.01%. Certainly, a small number. Of those 102, most were mild but eight people were hospitalized and two died. It is a message that says even with the vaccine, it is possible to become infected and it is possible, although remotely, to have a very severe infection.
In South Carolina, as of April 12, the Health Department has reported 155 breakthrough infections out of about 950,000 fully vaccinated residents or a rate of about 0.02%. In Oregon, as of April 8th, breakthrough infections occurred with three deaths among 700,000 fully vaccinated individuals for a rate of 0.024%.
In the Los Angeles area, two large health care providers, UCLA and USC, started doing weekly nasal swab tests on a proportion of their healthcare workers. Then, after some 15,000 staff at the two institutions were fifteen days post their second dose of either the Pfizer or Moderna vaccine, and with 4,167 of these tested weekly, there were seven individuals who tested positive for a rate of 0.05%. Some were asymptomatic and some symptomatic; none were serious.
The Centers for Disease Control, in a report dated on April 15th and which will be updated regularly, notes that with more than seventy-seven million Americans two weeks after full vaccination, 5,814 breakthrough infections have been reported across the country for a rate of 0.008%. The CDC points out that it is probable not all breakthroughs have been reported, certainly not all asymptomatic infections and probably not all mild infections. Still the risk rate is very low. It is worth noting however that most people have only been vaccinated for a few months at best. So, it is possible and in fact likely that, over more time, more of these breakthrough infections are be expected. Among the 5800 individuals, 396 were admitted to the hospital and 74 died although nine died for reasons other than from Covid-19.
Why do breakthroughs occur? The reasons are murky at best.
Certainly, older individuals and immunocompromised individuals may have a reduced immune response to the vaccine. The big clinical trials excluded those with a known suppressed immune condition so their responsiveness to the vaccines was not evaluated. But vaccines in general are known to be less effective in older individuals with lessened immunity, those on immune suppressing drugs and those with diseases or conditions that limit a strong immune response to a vaccine. An early study of kidney transplant patients showed that there was a very limited antibody response to the first dose of the Pfizer or the Moderna vaccine with most having no measurable response at all.
Some people may come in contact with a person exhaling a very high viral load which would be especially dangerous in a confined space. This might occur in a setting such as an elevator where someone who is infected is transmitting the virus in large numbers and this overwhelms the recipient’s immune response.
It is also possible that some of the variants such as the ones from the United Kingdom, South Africa or from Brazil are more transmissible and more dangerous in causing disease among vaccinated individuals. The authorized vaccines have been generally effective against the variants but not quite as good. Still, it is possible that breakthroughs may turn out to be more common with some of the variants. Only time will tell. The Centers for Disease Control is trying to determine for each person who has a breakthrough whether or not it is due to a variant or to the original strain.
For many, especially younger individuals with no underlying risk factors, the reasons why a breakthrough occurred are just not clear. As of now, many if not most people, cannot determine where they might have “caught it.” This means they are surprised and often stressed when they develop infection. As one person said, “I was supposed to be safe.”
Meanwhile, the CDC has posted recommendations on what fully vaccinated people should consider with regard to breakthroughs.
Should you worry? No.
But you should be proactive. Case counts are not down enough to be complacent; unfortunately, they are rising in many areas of the United States. This is just another reminder why it is still important to wear a mask, do social distancing, avoid crowded settings, avoid areas where there are limited air exchanges (like that elevator) and do wash your hands frequently. And if you are immunosuppressed from disease, frailty, medications, or advanced age, be extra careful. For all of us, it is important to remember that you are following these precautions for your own sake for sure but you are also doing it for the sake of others, especially the most vulnerable. We all need to be good neighbors.