Nearly one in four people on the planet has received at least one dose of the coronavirus vaccine, and nearly one in two people in wealthy countries in Europe and North America. As the number of people vaccinated with Covid-19 increases around the world, there is growing talk of imminent victory over the epidemic, reopening borders, restoring transportation links and returning to pre-pandemic life.
But even in wealthy countries where vaccination is in full swing, the WHO advises not only not to remove masks, but also to be cautious about lifting other restrictive measures. How effective is the vaccine in preventing transmission of the virus – and when will it be possible to take off the masks?
A month ago, when a 37-year-old patient at a mental health facility in Singapore was found to have COVID-19, the facility’s management did not panic. Due to the nature of the facility, all staff and most of the fragile residents have been vaccinated against Covid-19 since February-March, as they are considered at risk. However, as a precautionary measure, the facility has been quarantined and all staff, patients and others who have had recent contact with the infected woman or her caregiver have been placed in quarantine and are undergoing regular testing. Over the next week, the virus was detected in three dozen people, including a 30-year-old caregiver from the Philippines, four other boarding school employees, and 26 permanent residents. The majority of those infected were fully vaccinated against Covid-19 (meaning they received both vaccine shots) and had no symptoms at the time of diagnosis.
Blue circle in center – a 37-year-old female patient; green circles – her vaccinated contacts who tested positive for the virus; gray circles – unvaccinated contacts. Vaccination does not provide complete, 100% protection against the virus, as confirmed by the WHO. Even if you receive both doses of the vaccine and allow the necessary time for the immune response to reach its maximum level, there is still a chance of contracting Covid-19, especially for those who neglect other protective measures. In addition, the response to the vaccine is largely individual. The body’s protective response may be significantly weaker in the elderly, people with chronic illnesses or those taking immunosuppressive drugs. This means that their risk of infection is higher even after vaccination.
However, as several studies have shown, even if a vaccinated person does contract Covid-19, the infection is often asymptomatic or, less commonly, relatively mild. “Vaccination saves lives, but vaccination alone will not solve the problem,” says the WHO. “It is necessary to continue to fight the spread of the virus by all possible means – especially when the majority of people are not vaccinated and Covid-19 is so widespread.”
Each drug was tested on an average of 30,000 to 40,000 volunteers, and many of them may have been infected with Covid-19 without even knowing it. We explain quickly, simply, and clearly what happened, why it matters, and what will happen next. The number of offers should remain: episodes. End of story: Podcast Advertising. The developers did not track other volunteers. If one of them became ill from Covid-19 but carried the infection asymptomatically, that case was not included in the infection statistics. Given that asymptomatic patients account for up to 86% of all infections, according to various estimates, for every confirmed diagnosis there are several unrecorded infections. And it is unknown how many volunteers (and each drug was tested on an average of 30-40 thousand people) have experienced similar illnesses.
The thing is, it is incredibly difficult to track such cases of transmission. In fact, in order to do so, it is necessary to regularly test everyone for the presence of the virus, including healthy individuals who have not yet encountered the virus, those who have already recovered, and those who have been vaccinated. Such attempts have been made repeatedly, but only within limited social groups. For example, in one experiment, volunteers, including American doctors, social workers, and other “frontline pandemic fighters,” were tested for coronavirus weekly for three months, regardless of symptoms or vaccination status. It was found that two doses of the vaccine reduced the likelihood of infection in the body by about 25 times.
Similar studies are being conducted by vaccine developers themselves, and early results look promising. The Johnson & Johnson drug, for example, was found to reduce the risk of asymptomatic infection by nearly three-quarters. Data from the mass vaccination in Israel show that people vaccinated with the Pfizer-BioNTech vaccine have a viral load (i.e., virus concentration in the blood) that is four and a half times lower in the event of infection than those who are not vaccinated. And a study conducted by Public Health England concluded that people who had received at least one dose of the vaccine (Pfizer or AstraZeneca) were half as likely to infect their household. Another similar study showed very similar results.
Overall, therefore, the situation looks quite optimistic, according to the experts. The problem is that all these studies are based on several logical, but not yet experimentally confirmed, assumptions. For example, it is known that both children and adults with symptoms have higher viral loads than asymptomatic patients. Based on this, scientists hypothesize that people with lower viral loads are less likely to cough and sneeze – and therefore less likely to infect others.
Infection is especially effective in closed spaces where people sit, eat, and talk close together. “The data available to date allow us to state with confidence that in the event of Covid-19 infection, the viral load in vaccinated individuals will be lower than in unvaccinated individuals,” said Professor Barbara Richardson of the Department of Global Health at Washington University. “In this case, the likelihood of a vaccinated person infecting an unvaccinated person will also be lower (although we cannot completely rule out the possibility of infection transmission in this way).”
To clear up the confusion and understand how the virus spreads differently in vaccinated and unvaccinated individuals, more extensive studies are needed, with careful monitoring of all social contacts. One such experiment is currently taking place in the state of Washington: initially, volunteers were to be recruited from local college students, but then any resident of the state between the ages of 18 and 30 was allowed to participate in the study. Volunteers who agreed to receive their dose of the vaccine with a four-month delay (or who refused vaccination altogether) will essentially become the control group for vaccinated individuals of the same age. Volunteers in both groups will be tested daily for coronavirus, while their close contacts will be tested twice a week. Scientists will study the differences in how the virus is transmitted within and between the two groups.
However, Professor Michael Lin, head of the bioengineering laboratory at Stanford University, says that some conclusions can be drawn from the observations already made. Vaccines definitely reduce the risk of further transmission of the virus [from a vaccinated person to others], reducing the risk of infection by 79-88%,” Professor Lin continues. – However, the [Singapore] clusters vividly demonstrate that if a vaccinated person is still infected, he or she can still transmit the infection to someone else. And under certain conditions (such as when people eat and talk in closed spaces), such transmission can be very effective.
Another cluster in Singapore. The green circles with more than one line from them are fully vaccinated individuals who were infected themselves and transmitted the infection to someone else. “Vaccinated individuals often have asymptomatic cases, but many of them are carriers of the virus,” summarizes the professor. The danger, he says, is that even in the bodies of asymptomatic vaccinated patients, the virus continues to multiply – and therefore can mutate. And it can be passed on – already in a modified form.
However, the BBC’s WHO correspondent reassured that there is nothing to worry about – at least for now: “Studies on how much the new variants of the virus can pose a threat in terms of the effectiveness of vaccines, diagnostic tests, etc. are ongoing, but – judging by the information at the moment – the vaccines continue to be effective.” If the vaccination campaign goes according to plan (and is not disrupted by a mutant strain against which existing vaccines will be ineffective), the coronavirus pandemic will gradually fade until Covid-19 becomes a common seasonal infection along with the common cold, flu, and other respiratory infections. Experts predict that this could happen as early as next summer.