Coronavirus: Can a vaccinated person still spread COVID?

After nearly two months, Israeli data begins to confirm what Pfizer already knew: their coronavirus vaccine stops symptomatic and severe COVID-19.

Why then do Israelites still wear masks for Purim only?

If people become infected with coronavirus in silence, they can pass it on, and it can make people who are not immune sick.

A model developed in January by researchers at the Centers for Disease Control and Prevention showed that asymptomatic people transmit more than half of all cases of the new coronavirus.

But there is growing evidence that people who are vaccinated do not spread the virus much, if at all.

The ideal vaccine is one that produces the so-called sterilizing immunity, which means that your immune system is able to prevent a pathogen, including viruses, from repeating inside your body. Not all vaccines reach this standard. The vaccines against measles and rubella, for example, provide it. The hepatitis B vaccine does not.

Although it is scientifically intuitive that a reduction in infection and transmission is accompanied by vaccination, and preliminary signs suggest that the vaccine does at least some of both, according to Cyrille Cohen, head of the immunotherapy laboratory at Bar-Ilan University, “we need evidence” and that these are extremely difficult studies to do.

The answer would have “obvious” and “major consequences” for people’s daily lives, said Eran Segal, a computer biologist at the Weizmann Institute of Science. This is because the vaccine must prevent transmission to bring about herd immunity.

The more the virus circulates, he explained, the more likely it is to mutate in a way that improves the ability to spread, such as the British variant, to make people sick or become vaccinated.

“If there are people from abroad who know that the chances are small that they will transmit the virus, we can let them go and they do not have to go into quarantine,” Segal explained. “But if you know that there is an insignificant chance that they can still transmit the virus, you need to pay attention to the variants.”

He said it was also related to the general opening of society, such as the ability to hold large concerts without concern. Or to hold the concerts without social distance and masks.

“Everyone must still be careful,” said prof. Gili Regev-Yochay, director of the Infectious Diseases Epidemiology Unit at Sheba Medical Center, said Tel Hashomer. ‘Things are getting more complicated now because people think they’ve been vaccinated and everything’s fine. It is therefore more difficult to keep the mask on. But it is necessary because we do know that some people become infected and will be asymptomatic. And those people might spread the disease.

“The problem is that if not everyone is vaccinated or people are immunosuppressed, even if they are vaccinated, the vaccine is less effective, they can contract the disease,” she continued.

REGEV-YOCHAY said several Israeli research teams are now investigating the demand for coronavirus vaccine transmission and “the results look very promising.”

Modern has shown early positive results that infected people are less likely to transmit the disease in the original report, which was submitted to the U.S. Food and Drug Administration in December when it obtained approval for emergency use.

During the phase III clinical trial, Moderna researchers challenged participants to see if they had the virus when they went for their second shot, and then compared the results of those who received the vaccine with the placebo.

They saw a two-thirds decrease in the number of asymptomatic infections among people who received the first shot compared to those who received the placebo.

In a supplement provided to the FDA, it showed that 14 of the 14,134 vaccines at the time had asymptomatic cases of coronavirus, compared to 38 of the 14,073 in the control group.

However, this was not the primary endpoint of Modern research. They only tested people twice – at the beginning and before the second shot, which put the shows apart by about a month – so they missed out on contagion.

The University of Oxford also selected participants on the virus in its clinical trial for AstraZeneca. Various reports from the university showed a 49% and 67% decrease in positive tests among the vaccinated compared to those who were not vaccinated.

Earlier this week, a Public Health England SIREN (SARS-COV2 Immunity and Re-Infection Evaluation) report was pre-printed by peer-reviewed medical journal Lancet, which assessed staff in UK public hospitals.

The study measured the impact of a single dose of Pfizer vaccine over an eight-week period and found strong evidence that vaccination of working-age adults would significantly reduce asymptomatic and symptomatic SARS-CoV-2 infection and the transmission of infection in the population. ”

Specifically, the report showed that there were 977 new infections during 710,587 person-days follow-up in the unvaccinated group, an incidence density of 14 infections per 10,000 person-days. In the vaccinated group, there were 71 new infections 21 days after the first dose, an incidence rate of eight per 10,000 people follow-up and nine new infections seven days after the second dose, an incidence rate of four per 10,000 person days of follow-up. Person time, as described by the North Carolina Institute for Public Health, is an estimate of the actual risk time that all participants contributed to a study.

“After checking for other risk factors, the efficacy of the vaccine against infection 21 days after the first dose of Pfizer vaccine was 70% in the study population and increased to 85% seven days after the second dose.”

Staff were PCR tested regardless of the symptoms to detect asymptomatic infection.

In Israel, where nearly 4.6 million people have been stabbed at least once, data is also beginning to emerge.

A pre-published study by the Ministry of Health and Pfizer, released by the media, showed that the vaccine infection, including asymptomatic infection, decreased by 89.4% in people who received two doses of vaccine compared to non-vaccinated .

However, as noted, the full report has not yet been released, and some scientists have said that the method of the report may have led to an overestimation of the vaccine’s effect.

Separately, a report by Sheba released in the Lancet earlier this month found that among more than 7,000 health workers who received their first dose of Pfizer vaccine in January, there was a 75% reduction in coronavirus cases within 15 to 28 days. wash.

According to the hospital’s Regev-Yochay, only 170 people became infected during the two-week period. Of those who contracted the virus, 99 showed symptoms. Eighty-nine of the patients were not vaccinated.

There is also another consideration regarding virus transmission, and that is viral load: how much virus can be measured in a patient, which will determine how much virus you spread in the air when you breathe or cough. The less virus you spread, the fewer people are likely to catch the virus from you.

The effect of vaccination on virus burden in coronavirus infections is still unknown, but some studies are also beginning to appear on this.

In a paper published earlier this month on Medrxiv, a non-peer-reviewed health science website, by researchers from the Technion-Israel Institute of Technology and Maccabi Health Services, it was reported that the average viral load was significantly 12 days after vaccination. decreased.

Analyze positive SARS-CoV-2 test results after vaccination with the BNT162b2 mRNA vaccine [the Pfizer vaccine], we find that the virus load is quadrupled for infections that occur 12-28 days after the first dose of vaccine, ”the report reads. “This reduced virus burden indicates a reduction in infectivity, which further contributes to the impact of the vaccine on the spread of viruses.”

The report was based on an observational study, not on a randomized, clinical trial. As such, it had several limitations.

One of the country’s largest test laboratories, MyHeritage, also published a study this month comparing the virus load of approximately 16,000 positive test results between 1 December and 30 January. The study hoped to evaluate whether there were any differences between the amount of virus present in people over 60 – the first people in the country to be vaccinated – and those between the ages of 40 and 59 who started vaccinating later.

The laboratory, along with researchers from some of the top universities in Israel, considered four two-week windows, the first three before most of the older population was vaccinated.

Israel began its vaccination campaign on December 20 with medical workers and the elderly, and by the end of the test period, about 80% of people over 60 in Israel received at least one vaccine, compared to about 30% or 40% of those ages 40 to 59. years old.

According to the study, those over 60 have reduced a virus load by 50% to 95% in the past two weeks.

But here, too, there were limitations, such as that the researchers did not know if the people being tested for coronavirus had been vaccinated at all, let alone with one or two shots.

Bar-Ilan’s Cohen said anecdotal evidence had also surfaced in the country as more people were vaccinated.

“We know, for example, that there was an anecdote that two vaccinated vaccines became infected by the virus, but no one in their immediate area at home or work got the virus from these people,” Cohen said.

“Somehow the vaccine was protective,” he continued. ‘But it’s just an anecdote. In science, we need real evidence, and it is very difficult to do such studies. ”

As noted, the original Pfizer, Moderna, or AstraZeneca trials were not set up to answer this question. Rather, they were intended to determine the safety and effectiveness of their vaccination candidates.

Volunteers in these types of clinical trials are usually divided into two groups – one receiving the vaccine candidate and the other one placebo. Once the number reaches a critical, predetermined test mass, the researchers compare the two groups to see if those who received the authentic jab performed better.

Pfizer and Moderna reported more than 90% efficacy, and the side effects were considered minor and minor.

THE REASON that transfer studies are not done in the first phase is that it takes a long time and is difficult to perform properly. Experts estimate that the evidence of reduced transmission is at least a few weeks, if not years.

“It’s no coincidence that Moderna and Pfizer did not set transmission prevention as one of their primary or secondary objectives in clinical trials on the vaccine, because it really takes time,” Cohen said. “You need to follow people who have been vaccinated for a long time and determine if they have infected other people.”

He said, for example, that you may take a family to which one person is vaccinated, and then you should test that person and his or her family members regularly to determine if someone has been infected by the vaccine. But Cohen said it was not infallible either, as family members could also be infected by an external source.

Segal said another way to do this is to track down a large group of tens of thousands of people from the point where they are vaccinated, and test them every week to see if they are really infected.

“It’s going to be over before it’s over,” Regev-Yochay said of the pandemic. “We’re still not there.”