As about 2 million people a day across the United States receive a dose of one of three COVID-19 vaccines, cases of the disease are declining again thanks in part to increased immunity. But while COVID-19 cases are declining, researchers are examining those that appear in a certain group of people: those who are completely vaccinated.
These cases, called advanced infections, are not unexpected. This is because vaccines are not 100 percent effective.
“When people hear about innovative infections, they automatically think‘ oh, these vaccines don’t work ’or‘ they’re not effective, ’” says Richard Teran, an epidemiologist with the U.S. Centers for Disease Control and Prevention’s Epidemic Intelligence Service. "That's just not true … most people who get the vaccine are protected against COVID infection and also from serious diseases."
The three jabs currently authorized for use in the United States – Pfizer, Moderna, and Johnson & Johnson – have been shown to be effective in preventing COVID-19 symptoms in clinical trials. And evidence is building that Pfizer and Moderna stings, both mRNA vaccines, frustrate infection in immunized people as well (SN: 30/03/21). People are considered completely vaccinated two weeks after receiving all doses of a vaccine.
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But when advances in coronavirus occur, there are several important questions that experts should keep in mind, says Francesca Torriani, an infectious disease physician and hospital epidemiologist at the University of California, San Diego.
Do advanced infections cause serious illness? Or do vaccinated people often have milder symptoms? Another question is whether the immunized people who are still infected transmit the virus to other people. Finally, did an immunized person catch the infection because his or her immune system did not start after receiving the shot? Or was it that the vaccine elicited an immune response that didn’t offer much protection against, perhaps, a variant of the coronavirus?
There has been some progress in answering these questions since COVID-19 vaccines began to become weapons in late 2020. Here is what researchers have learned so far.
Of the more than 95 million people in the United States who have been completely vaccinated, only 9,245 (or 0.01 percent) have been infected with the coronavirus as of April 26, according to the CDC. Just over a quarter of those people never had symptoms; 132 people died, or 1 percent of advanced infections. Twenty of these deaths occurred in asymptomatic individuals or were probably unrelated to COVID-19.
Studies analyzing vaccinated people in the real world show that not only are advanced cases of COVID-19 rare (at least based on mRNA vaccine analyzes; there has been less time to study J&J firing), but they are also declining the chances of serious illness. Moreover, there are indications that vaccinated people are less likely to transmit the virus to others (SN: 2/12/21).
In Chicago, for example, vaccines have helped stop the spread of coronavirus in skilled nursing facilities, which have been hit hard in the pandemic due to high risk of exposure and residents at risk of becoming seriously ill. Among 14,765 residents and staff members completely vaccinated, only 22 people contracted the virus more than two weeks after their second dose of Moderna jab, Teran and colleagues reported in the April 30 Weekly Morbidity and Mortality Report.
Most of those 22 people were asymptomatic or had mild symptoms, but two were hospitalized for COVID-19. One person, who had several underlying conditions, died. But there have been no additional cases dating back to advanced infections, suggesting that the risk of transmission of infected vaccinated people is low.
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More work needs to be done to improve the risk of transmission of vaccinated people and whether older people with underlying conditions may be more likely to have an advanced infection. But “I think (the study) really shows that vaccines are working,” Teran says. And the shootings are "our most important tool to stop the transmission of COVID and finally slow down this pandemic here in the United States."
The key to finding innovative infections is to do a lot of testing, says Torriani, who co-authored a March 23 letter from the New England Journal of Medicine describing the success of mRNA vaccines in protecting Southern California health care workers. It is possible that an infected person has no symptoms or only mild ones, which means that cases can easily fly under the radar or be confused with things like the common cold. Therefore, the current CDC counts are likely to be underestimated.
Vaccines and variants
One aspect of the ongoing pandemic that experts are meticulously observing is the emergence of coronavirus variants. Some mutations in the coronavirus could help it bypass immune responses in vaccinated people, which may require a booster shot to provide better protection.
Researchers reported on April 9 in a preliminary study published on medRxiv.org in Israel, for example, people vaccinated with Pfizer shot are more likely to become infected with a variant first identified in the UK or South Africa compared to people not vaccinated. . Unvaccinated people, on the other hand, are vulnerable to all versions of the coronavirus.
But cases in vaccinated people appeared to occur in a particular period of time, says Adi Stern, an evolutionary virologist at Tel Aviv University. People who caught the version of the virus that emerged in the UK were more likely to receive just one dose of vaccine, perhaps because they did not yet have full protection. Those who received two doses were more likely to become infected with the South African version, but only up to two weeks after the shot.
After that two-week period, Stern and colleagues saw no advanced cases of the South African variant. Although this variant is not very common in Israel, which could mean that such cases are simply difficult to find. “What we think is happening is that immunity hasn’t reached its peak, which is on track to reach it,” Stern says. “That’s when we think there’s an advantage” to the variant.
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In some rare cases, infections can occur even in the face of a strong immune response from a vaccine. A patient in New York, for example, developed symptoms of COVID-19 19 days after receiving a second dose of Moderna jab, despite having high levels of protective antibodies, the researchers reported April 21 online in New England Journal of Medicine. The virus responsible for the infection had a mutation designed to help the coronavirus bypass the immune system. The researchers point out that it is possible for the patient to become infected before the second shot took effect.
Still, it’s important for experts to be aware of these cases and use them to gather more information, says Ezgi Hacisuleyman, an RNA biochemist at Rockefeller University in New York City and co-author of the study. Thus, if there is an increase in cases in immunized individuals, researchers can quickly identify them and determine if this is a case of a variant of coronavirus that surrounds a strong immune response.
For now, there are not enough advanced variants-linked infections to deserve the use of updated shots. “There will be (advanced infections) no matter what,” Stern says. "We need to be on the lookout for variants, but I still think we also have to rely on the vaccine itself because we have evidence: it works."