1. What happened with the blood clots?
Reports that some vaccine recipients developed blood clots prompted several countries, mainly in Europe, to suspend use either of all AstraZeneca Plc’s Covid vaccine or doses from a particular batch, or to restrict its use in younger people. The European Medicines Agency concluded April 7 that unusual blood clots with low blood platelets should be listed as a very rare side effect of the vaccine; the same day, officials of the U.K.’s medicines regulator said evidence of the connection was firming up. Among 86 cases the EMA examined up to March 22, there were 18 deaths. U.K. regulators put the overall risk of the clots at about 4 in a million people who receive the vaccine. Most reported cases occurred within two weeks of vaccination, according to the EMA. Symptoms include shortness of breath, chest pain, leg swelling, persistent belly pain, severe headaches, blurred vision and tiny blood spots under the skin beyond the vaccine injection site. European regulators stressed that the overall benefits of the AstraZeneca vaccine outweigh the risks of side effects. U.K. health authorities noted that preliminary evidence suggests the clots occur more often in young people and recommended that those younger than 30 be offered an alternative vaccine, if available.
2. What’s causing the clots?
U.K. health officials described the clotting syndrome as similar to a rare side effect of treatment with heparin, an anticoagulant, in which the body forms antibodies against blood platelets. How or why the vaccine might be involved in such a process is still under investigation.
3. Have clots been seen with other Covid vaccines?
Four serious cases of unusual clots accompanied by low blood platelets, one of which was fatal, have occurred after vaccination with the Covid vaccine from Johnson & Johnson, the EMA said April 9, announcing an investigation. One of the cases happened during a clinical trial. At the time, the company said it had found no evidence the vaccine was at fault. Three others occurred in the U.S. Both the J&J and AstraZeneca shots use a harmless version of an adenovirus — the cause of some common colds — to deliver a gene that instructs our cells to make the spike protein that gives the coronavirus that causes Covid its crown-like appearance. This, in turn, stimulates the body to mount immune responses to the virus, so that it is primed for a fight if it ever encounters the real thing.
4. What about the serious allergic reactions? What accounts for them?
The body fights foreign invaders through a variety of mechanisms that include making protective proteins called antibodies, releasing toxins that kill microbes, and marshaling guardian cells to battle the infection. As in any conflict, sometimes the effort to repel an infection can itself be damaging. In rare cases, it can produce runaway inflammation and swelling of tissues in a serious allergic reaction called anaphylaxis. As much as 5% of the U.S. population has had such a reaction to various substances. It can be fatal if, for example, the person’s airway swells shut, though deaths are rare. Allergies to insect stings and foods can provoke it, though drug reactions are the most common cause of anaphylaxis fatalities in the U.S. and U.K. As of April 5 in the U.S., no deaths had been connected to Covid vaccines, from anaphylaxis or any other reaction.
5. How often have Covid vaccines triggered cases?
In the U.S., according to the CDC, it occurs in just 2 to 5 people for every million receiving a Covid vaccine. The risk of contracting Covid outweighs that posed by the vaccines, officials and clinicians say. Anaphylaxis is a known risk of vaccination. Such reactions occur about 1.3 times per million doses of flu vaccine administered. With other vaccines they have been seen at rates of 12 to 25 per million doses, though the studies were small. When anaphylaxis occurs, it is almost always within half an hour of administering the vaccine, according to the CDC.
6. What’s being done to manage the risk?
The U.K. and U.S. have advised people who have allergies to any component of a Covid vaccine not to receive it. Anaphylaxis can be quickly countered with antihistamines in tandem with adrenaline injectors like Mylan NV’s Epi-Pen that slow or halt immune reactions, and health workers giving the vaccine are keeping such items at the ready. These treatments don’t cancel out the beneficial effects of vaccines. In the U.S., health workers are observing everyone who receives the vaccine for at least 15 minutes post-injection to watch for signs of a reaction; those with a worrying history of allergic reaction are monitored for twice as long. People who have had reactions to a first dose of vaccine shouldn’t receive a second, according to the CDC.
7. Do we know what in the shots is causing anaphylaxic reactions?
That isn’t clear. Two leading candidates are polyethylene glycol — a chemical found in many foods, cosmetics and medications — and lipid nanoparticles that encapsulate the messenger RNA, a genetic component in the Moderna and Pfizer-BioNTech vaccines, according to Eric Topol, a clinical trials expert and director of the Scripps Research Translational Institute. Polyethylene glycol has been previously linked to a handful of anaphylaxis cases. Once a cause has been narrowed down, it may be possible to make Covid vaccines even safer than they are now, Topol said.
8. What about the cases of Bell’s palsy?
In studies testing the Moderna and Pfizer-BioNTech inoculations, more people developed Bell’s palsy, which typically affects just one side of the face, after receiving vaccine doses than placebo shots. The imbalance turned out not to be substantiated, however, based on the massive safety database the CDC has collected on millions of people vaccinated since the drugs were authorized for the general public. Also, the drugs regulator in the U.K., where the Pfizer-BioNTech formulation is one of two in use, noted that as of March 28, the number of reports of Bell’s palsy among those vaccinated does not suggest an increased risk.
9. What’s known about deaths after vaccinations?
• Norwegian officials were the first to report people dying after being inoculated, saying in mid-January that 33 people age 75 and older had died a short time after receiving the Covid vaccine developed by Pfizer Inc. and BioNTech SE. After a review, a committee of the World Health Organization said that the fatalities were “in line with the expected, all-cause mortality rates and causes of death in the sub-population of frail, elderly individuals.” The committee concluded that the risk-benefit balance of the vaccine “remains favorable in the elderly.”
• The U.K.’s Medicines and Healthcare Products Regulatory Agency reported that, through March 28, there were 302 deaths shortly after injections with the Pfizer-BioNTech vaccine, 472 after the AstraZeneca shot and 12 where the brand was unspecified. The deaths were mainly in elderly people or those with underlying illness, and the evidence does not suggest the vaccines played a role, it said. However, the agency’s April analysis of blood clots after vaccinations reported 19 deaths among 79 cases and officials said further study was needed.
• Germany’s medical regulatory body, the Paul Ehrlich Institute, said after an investigation that the deaths of seven elderly people shortly after receiving the Pfizer-BioNTech vaccine were probably due to the patients’ underlying diseases.
• In the U.S., which is using vaccines from Pfizer-BioNTech, Moderna Inc. and Johnson & Johnson, the Centers for Disease Control and Prevention said that as of April 5, there were 2,794 reported deaths among inoculated people, a rate of 0.002%, and no evidence suggests a link.
• Authorities in Hong Kong, which has mostly deployed a vaccine from China’s Sinovac Biotech Ltd., have reported six deaths among more than 150,000 people inoculated. None have been connected to vaccines.
(Updates with new section 3 on blood clots after J&J vaccines.)