A successful fourth shot could serve as a model for other countries this year, although some health experts doubt whether a fourth shot is needed at this point in the pandemic in fighting COVID-19.
The latest nation to provide a second booster was Chile, a country of 19 million that has already vaccinated more than 45 million, making its vaccination campaign one of the most successful in the world. According to the Chilean government, more than half of those shots were from China’s Sinovac Biotech Ltd, with about 12 million Chileans receiving the first two doses from that vaccine-maker. Officials vaccinated about 46% of Chileans from Pfizer and AstraZeneca plc.
On Monday, health officials gave the Pfizer vaccine to people with weakened immune systems who were thought to be particularly vulnerable to the virus.
Ana Perez, 57, who has stage 4 bone cancer, said moments before receiving the booster under a giant tent on the north-eastern edge of the capital, Santiago, “I came right away when I was scheduled.”
Like many Chileans, she was fully vaccinated with a vaccine made by Sinovac, which has been used in most of Latin America. It now has two Pfizer boosters, which Chilean officials say are necessary as the effectiveness of Chinese-made vaccines decreases and more infectious forms appear.
“I was so scared of getting Covid,” said Ms. Perez. “I hope everyone in my position will come [to get the booster],
Chile joined Israel and Brazil in delivering the second booster.
In Brazil, the states of So Paulo and Rio de Janeiro have been providing a second booster to people with challenging health conditions such as cancer and HIV/AIDS since late December. Halfway around the world, Israeli health officials began giving immunocompromised people a fourth dose in late December before starting to provide a second booster to people age 60 and older.
Israeli officials based their decision to give a fourth shot on the hope that the Omicron version would propel through the country, and due to research showing that the protection provided from the initial booster would fade within three to four months.
The head of the Israel Association of Public Health Physicians and a member of the Israeli government advisory panel, Prof. “We’ve started to see weaker immunity in terms of antibodies, and we see success with the Omicron version as well,” Nadav Davydovich said. He said the priority is to provide the fourth dose to high-risk people and healthcare workers.
Israel’s Prime Minister Naftali Bennett last week announced preliminary results from a trial at the Sheba Medical Center in central Israel that showed a five-fold increase in antibodies in people a week after they received Pfizer’s fourth shot of the vaccine. The vaccine was given to 154 medical workers of various ages four months after their third dose.
Securing booster shots has been a priority for officials in some developing countries that relied on Chinese vaccines that have proven less effective than Western-made shots.
Akiko Iwasaki, a professor of immunobiology at Yale, said a study published on the MedRxiv website before peer review in late December found that people in the Dominican Republic who received two doses of the Sinovac vaccine had no neutralizing antibodies to Omicron. There was no detectable level. University that co-authored the study.
“I see benefit in giving a second booster,” Dr. Iwasaki said.
Not all scientists agree. Some say the fourth shot is premature and question whether another booster is really needed to prevent people from being hospitalized or worse.
Dr. Paul Offit, an infectious disease expert and a member of the US Food and Drug Administration’s advisory panel on vaccines, said the data suggests that the two doses provide strong protection against serious illness from COVID-19. He said it was expected that the vaccine’s protection against infection would decline after a few months.
“If the goal of a vaccine is to try to prevent mild disease, I don’t see that as a reasonable goal, nor do I see it as a sustainable public health strategy,” he said. “The real problem in this pandemic is not the people who have got two doses or three doses. The real problem is people who haven’t received any supplements.
Dr Gili Regev-Yochay, director of Israel’s Infectious Disease Epidemiology Unit of Sheba, said he is still not sure about the fourth shot because it is not yet clear how long the increased antibodies will last.
“Regarding the fourth dose, I’m not at all sure,” said Dr. Regev-Yoche. “I think that’s why it should be done in clinical trials.”
In the UK, the body advising the government on vaccinations said last week a second booster shot was not a priority. The first booster was still providing good protection against critical illness and the second shot would provide only limited additional protection against critical disease “at this time”.
The UK group said protection against mild infections would probably require a booster vaccination every three months, which was not a sustainable strategy. It said alternative vaccines may be available in 2022 that may be better able to provide long-term protection against Omron or other new variants.
Still, officials in countries like Chile are running ahead.
With the outbreak of Omicron, Chile is seeing a surge of new infections, reaching nearly 4,000 cases on Monday, and the government says daily cases could rise to 10,000 next week. The positivity rate now stands at 7.24%, the highest since June 2021.
Nevertheless, the seven-day average for death has not risen above 20 a day since the beginning of the year, reflecting clinical data and laboratory results that suggest Omron is higher than other types. It is lighter when transmitted more.
In February, Chile will begin giving a fourth dose to the general public, starting with people age 55 and older, regardless of their health condition. And the government of outgoing President Sebastian Pinera says it is securing supplies for a fifth dose, or third booster, for the new administration that took power in March.
“We will move at maximum speed,” Mr Pinera said on Monday from a vaccination site at the Chilean Air Force Hospital in Santiago.
Chilean antibodies need a second booster to strengthen immunity, said Claudia Cortés, an infectious disease specialist at the University of Chile, adding that it is not clear when the best moment for the general population would be to get a fourth shot. . “There is no information from a scientific publication that says what is the best moment to give a second booster, if it is now, or a few months later,” she said.
For now, 78% of Chileans approve of the government’s handling of the pandemic, according to a new survey by Cadem.
Bernadita Puga, a 57-year-old schoolteacher undergoing treatment for breast cancer, was excited about her fourth shot, which she received on Monday.
“I feel so happy and calm,” she told a vaccination tent in the Santiago neighborhood of Lo Barnachia. “Now, I feel more secure.”
—Luciana Magalhees in So Paulo contributed to this article.
Write Ryan Dube at [email protected]