Boston Hemophilia Center

Contact the Boston Hemophilia Center 617-355-6101
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Contact the Boston Hemophilia Center 617-355-6101
International +1-617-355-5209

Facts About Vacs

by Aric Parnes, MD, Adult Hematologist, BHC

Our immune systems have memory. They remember what they’ve seen. So the next time, our immune system sees it…Bam! Edward Jenner is credited with the first vaccination in 1796, starting with smallpox. He actually used a similar virus to smallpox — cowpox — after noticing farm workers, who contracted cowpox, never contracted smallpox. By injecting cowpox into people, he prevented the spread of smallpox, essentially tricking the immune system to fight a virus it had never seen.

The concept today is similar. We take small amounts of weakened virus or bacteria, or their parts, and inject it into people to educate immune systems, so defenses are ready for a counter-attack should the walls ever be breached again by something similar. And, oh boy, does it work! Regarding safety and effectiveness, fewer aspects of medicine and science come with more data and experience than vaccinations (literally 225 years of proof!). Besides an enormous volume of scientific study, the real proof is in the track record. Check it out: tetanus, pertussis (whooping cough), diphtheria, polio, measles, mumps, rubella, chicken pox, hepatitis A, hepatitis B, yellow fever, cholera, tuberculosis, Yersinia (the Plague). This long list of villains is no longer free to terrorize us (at least in our country). Thank you, vaccines. Other vaccines that protect us include pneumococcus (pneumonia), influenza (the flu), Haemophilus influenza B (HiB), rotavirus, human papilloma virus (HPV), zoster (shingles), and rabies. Jonas Salk developed the polio vaccine in 1955. Before that, polio killed 2000 to 3000 people in the U.S. each year and left thousands more paralyzed. At the time, it was considered the number one health concern in the country. Fast forward 65 years, polio is gone, but a new nemesis has emerged: COVID-19, and in just one year, it has killed 500,000 Americans and counting.

Some vaccines work better than others. The polio vaccine is 99% effective. Similarly, COVID-19 vaccines from Moderna and Pfizer are 95% effective (see table on page 6). The new vaccine from Johnson & Johnson is 70% effective, which does not sound as impressive, but if we were all vaccinated with Johnson & Johnson’s vaccine, we would reach herd immunity, and life as we remember it would be restored. These effective rates measure how often people catch the infection despite vaccination. The effectiveness for all three COVID-19 vaccines is even better when measuring prevention of hospitalization or death. Mortality (death) from COVID-19 plummets to nearly zero for those who are vaccinated.

The influenza vaccine is 40% effective at preventing influenza infection. Influenza is tricky because every year it changes. New strains that our immune systems no longer recognize appear. Fortunately, the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC) track the circulating strains day after day, so that each flu season, we can update our immunity and stay safer by re-vaccinating against the latest strains. Admittedly, flu vaccine could be better and new mRNA technology, similar to what is used in the COVID-19 vaccines, may be the key to making it better.

In cells, our genes are coded as DNA, and that DNA is copied into a mirror image called RNA. RNA is used to convert the genetic code into protein and protein then does all the work, transporting nutrients, providing cellular and organ function and structure, managing metabolism, and more. Vaccine science has evolved into locating the most immunogenic component of the invading organism. In other words, the part that our immune systems can most successfully attack. For SARSCoV- 2 (better known as COVID-19), these key parts are the spikes on its surface, the projections that make it look like a crown (thus its name Coronavirus).

Johnson & Johnson’s vaccine uses a piece of DNA that codes for these COVID spike proteins. That DNA segment is packaged into a weak virus called adenovirus 26 and injected into people. From there, the DNA enters our cells and our cellular machinery converts the DNA to RNA and then into protein — the COVID-19 spike protein. These spike proteins without the COVID-19 virus are harmless, but our immune system sees them and, knowing they should not be present in our bodies, forms antibodies to attack it. Those antibodies will protect us should the real COVID-19 virus enter through the lungs.

The Moderna and Pfizer vaccines work in a similar way, but skip the first/DNA step. Instead, they jump straight to the RNA, specifically messenger RNA (mRNA), which is RNA ready to be translated into protein, and then (this may sound familiar), our bodies make the COVID-19 spike proteins and our immune systems make antibodies against the spike proteins and those antibodies protect us. All vaccine pathways end at the same place: antibodies that protect us. By using only the mRNA or only the DNA that codes the spike proteins, we receive the smallest piece of the virus possible, while still providing maximum immunity. Many people express concerns about receiving genetic material, such as DNA or RNA from vaccines. These questions are logical. Will this vaccine change my DNA? Can it affect who I am or my future children? Can it cause cancer? The answer to these questions is an absolute, NO.

The DNA and RNA sit in the cells ready to code for the spike protein and then eventually degrade. That’s it. They do not incorporate into our DNA. They do not change our DNA. Another way to think about it is this: Did you know that the same genetic material was in all previous vaccines? Yes, it’s true. Because previous vaccines contained the whole virus or bacteria, only in a weakened form, they also contained the genetic material of those organisms. So what you get with DNA/RNA vaccines is not only less of the virus than before, but also the most important part — the code to the spike protein, which is the protein that binds to our lungs. A major advantage of the new DNA/RNA vaccine technology is that catching COVID-19 infection directly from the vaccine is impossible, because the whole virus itself is not in the vaccine. However, it is still possible to catch COVID-19 infection from the community after getting the vaccine, because the vaccines are not 100% effective. Therefore, we need to keep wearing our masks after vaccination.


Depending on the year, between 10,000 and 60,000 people die each year from influenza in the U.S. (according to the CDC), and up to 810,000 people are hospitalized with it (see CDC Figure). Despite the low effectiveness rates of the influenza vaccine, it still manages to save lives — and lots of them. The CDC estimates flu vaccines already prevent 3,000 to 12,000 deaths a year (in the U.S.) and up to 105,000 hospital stays and up to 7.5 million symptomatic infections each year. These numbers are staggering when you also consider saved school/work days and saved health and quality of life. Remember, these numbers reflect the benefits of a vaccine with only 40% effectiveness and when only 45% of all people in the U.S. bother to get it. Just imagine the illness prevented and the lives saved if we all got the flu shot each year (added benefit with herd immunity) or better yet, if we all got the flu shot and it had the same effectiveness COVID-19 vaccines have.

Table: Vaccines against COVID-19

 Data courtesy of the CDC 

Herd immunity means enough people in the community are immune to prevent the disease from spreading. Herd immunity for COVID-19 is expected to be achieved when 70-75% of all people are immune, whether through vaccination or past infection. Becoming immune through vaccination is much better than through infection, since a significant number of people will not survive the infection. Also, the real benefits of vaccination are not isolated to the individual but for the entire community, since the virus can no longer spread once herd (that is, community) immunity is reached.

Is there a down-side to getting the COVID-19 vaccine?

Symptoms are common. Allergic reactions can occur, rarely severe. The key allergen inside the two mRNA vaccines is polyethylene glycol (PEG). People with a known allergy to PEG can still get the Johnson & Johnson vaccine, since it does not contain PEG.

Worldwide, 228 million doses of COVID-19 vaccine have been administered, with 68 million in the U.S. This exciting news parallels the plummeting trends we have all watched on the daily tracker of new cases, evidence proving we can all contribute in this fight. Soreness at the injection site will occur in 75% of people. About 25% of people report a fever after the second dose (according to the CDC v-safe smartphone tracking app) and 40% feel achy. That is a lot, yet preferable to dying from COVID-19 and preferable to sequestering in our homes for yet another year, not able to go to a restaurant or the movies, or see our loved ones. As one of my patients said, regarding the one or two days of post-vaccine symptoms, “That’s a small price to pay.”

My personal journey: I received the first dose the week of Christmas as I was pulled in for urgent back-up in the hospital, making rounds on a number of patients with COVID-19 that week. After receiving dose #2, I had fever, chills, and muscle aches, and I could barely get out of bed the next day. Yet, I felt relieved, relieved that once the sideeffects wore off, I could go to work, continue to care for my patients who have or don’t have COVID-19, and know my protection went far beyond the mask and gown I continue to wear. I also felt happy, knowing that getting vaccinated will protect my family and anyone else in my circle.

The World Federation of Hemophilia (WFH) recently released its vaccination guidelines for people with bleeding disorders. First and foremost, the WFH notes that vaccines are safe, and it encourage all people with bleeding disorders to get vaccinated. Second, patients with mild bleeding disorders can proceed with the COVID-19 vaccination. Patients with moderate or severe bleeding disorders should discuss with their hematologists what the safest approach would be. Many will need to infuse factor or take some other medication for prevention of bleeding prior to receiving the vaccine.

Unfortunately, the clinical trials for all three COVID-19 vaccines did not include children, and therefore no vaccination is available for people under the age of 18 outside of a clinical trial. This important work is in progress. Fortunately, younger people are less at risk for symptomatic infection from COVID-19.

In summary, vaccines are safe, even for people with bleeding disorders. Vaccines save lives. They are highly effective for preventing COVID-19 infection and profoundly diminish the chance of dying from it. The vaccines take advantage of a new DNA/RNA technology that allows a more targeted approach to stopping infection. This genetic approach will also transform vaccines for other diseases and allow rapid development of targeted prevention. Production and logistical challenges have slowed the roll out, but once we have enough vaccine available for everyone (and that will be soon), we must all chip in to reach herd immunity and protect the community. So let’s roll up our sleeves and get to work.


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