Why the Covid-19 vaccines do not stop the virus from circulating

Covid-19 vaccines prevent hospitalizations and death from the disease in more than 90% of cases, but they do not stop the transmission of the virus. That’s why cases among the vaccinated are to be expected: a person who has been fully immunized can still contract SARS-CoV-2 and spread it to others, even if they too are vaccinated.

In Spain, contagions have been rising despite the fact that 79% of the population is fully vaccinated against Covid-19. According to the latest Health Ministry report, released Thursday evening, the 14-day incidence rate has jumped to 104 cases per 100,000 inhabitants, up eight points since Wednesday. This is the first time the data point has risen above 100 cases in two months.

Meanwhile, in the regions of Navarre and the Basque Country the incidence rate is more than double the national average, coming in at 278 cases and 221 cases per 100,000 inhabitants, respectively. The Health Ministry reported 6,315 new infections on Wednesday and added 29 deaths to the official toll, which now stands at 87,804.

Pressure on hospitals is also rising. According to the latest figures, 2,308 Covid-19 patients are in hospital, equating to an occupancy rate of 1.86%, up from 1.82% on Wednesday. In intensive care units (ICUs), 5% of beds are occupied by Covid-19 patients, who number 457. According to the Health Ministry’s proposed traffic light system, a situation can be considered under control if the occupancy rate for hospital wards and ICUs is below 2% and 5%, respectively.

With infections rising, EL PAÍS looks at the role of Covid-19 vaccines in preventing contagion and serious cases of the disease.

Do vaccines help prevent infection?

Yes, although it is not known to what degree. Initial clinical trials on the effectiveness of the vaccines were not able to investigate this issue in depth given the conditions of the studies. To properly assess whether the vaccines prevent infection, researchers had to wait until vaccines were rolled out in the real world.

A study carried out in April on this subject, which looked at vaccine effectiveness among 4,000 healthcare personnel and essential workers in the United States, found that the Pfizer-BioNTech and Moderna vaccines prevented 90% of coronavirus cases. Another study, which was carried out when the more-contagious delta variant had become dominant, found that the vaccines’ effectiveness at preventing infections had dropped significantly – to 51% in the case of Pfizer and 73% for Moderna.

In Spain, vaccines are between 70 and 90% effective at stopping contagions, according to the latest Health Ministry report on the issue, which was published October 3. “High global effectiveness is maintained even after several months have passed since vaccination and after the arrival and expansion of the delta variant at the end of June,” the study states.

Can you contract a serious case of Covid-19 if you are vaccinated?

The vaccines approved for use in Spain – Pfizer-BioNTech, Moderna, Oxford-AstraZeneca and Janssen – are not 100% effective, meaning it is possible for vaccinated people to develop a serious case of Covid-19. But the large majority of serious cases are being recorded among the unvaccinated. According to data from the regions, six in 10 coronavirus patients in intensive care in Spain are unvaccinated. People who are immunized have 10 times more protection against developing serious illness.

What percentage of the vaccinated develop serious cases of Covid-19?

This is very difficult to determine and depends on the situation in each country. In all cases, however, the figure is extremely low. In the US, the infection rate among the vaccinated is between 0.01% and 0.54%, according to a study by the Kaiser Family Foundation, published at the end of June. The rate of hospitalization and death is also very low: 0.06% and 0.01%, respectively. A similar incidence for Covid-19 deaths was recorded in Israel.

What is happening in Spain?

The Spanish Health Ministry does not provide data on the vaccination status of new coronavirus infections nor of the Covid-19 patients in ICUs, despite repeated requests from this newspaper. What is known is that most of the patients with serious cases of Covid-19 are unvaccinated. The vaccines are 90% effective at preventing hospitalizations among the under-80s, and 87% effective for those over the age of 80, according to the Health Ministry report from October 3. This study also found that although vaccine effectiveness falls slightly after five or more months, for the over-80 population the shots remain “considerably” effective at preventing infection and hospitalization.

Will everyone need a vaccine booster shot?

There is so far no data that supports giving a booster shot to healthy people under the age of 80, says Marcos López-Hoyos, the president of the Spanish Immunology Society. The expert indicates that the serious Covid-19 cases among the vaccinated are only being recorded among patients with existing health conditions and those over the age of 80. It is not clear why, but part of the explanation may be due to the impact of age on the immune system and because the over-80 population tends to have the most additional health conditions. “This is the collective that must receive a third dose. Right now, there is no reliable data that indicates it is needed for anyone else,” says López-Hoyos.

Can vaccines stop the virus from spreading?

The available vaccines alone cannot stop the spread of the virus. But vaccination, combined with basic preventive measures such as proper hygiene, face masks and social distancing where needed, lowers transmission significantly. Simply wearing a face mask reduces the incidence of the coronavirus by more than 50%, according to a study based on data from 200 countries and published in the medical journal BMJ. For López-Hoyos, this is clearly the reason why countries such as Austria and Germany are seeing such a sharp rise in infections. “In these countries, fewer people are vaccinated, and despite this, they relaxed basic protection measures earlier. This should make us think that we need to maintain the use of face masks and the rest of the basic hygiene measures, because right now, it is the only way we have to curb the transmission of the virus,” he says.

What will happen with the coronavirus?

In January of this year, a group of experts in viral evolution predicted that Covid-19 will become an asymptomatic infection, or at worst, a minor cold, between one and 10 years. But SARS-CoV-2 will never disappear, they said. Right now, this is the most plausible scenario for countries with high vaccination rates such as Spain, says López-Hoyos. Like many other infections, including the flu, there will be the odd serious case among vulnerable people and some deaths will be inevitable. But in general, the population will be protected by the vaccine and preventive measures.

Could a more lethal variant of the coronavirus emerge?

It’s possible, but unlikely. So far, the variants that are more resistant the body’s immune system, and therefore, can lead to more serious illness – the gamma first detected in Brazil and the beta first identified in South Africa – have not become dominant. Instead, it is the strains of the coronavirus that are more transmissible – the delta first detected in India and the alpha first detected in England – that account for most cases.