With hundreds of millions of people vaccinated against COVID-19, the outbreak should begin to die down in places where a large chunk of the population has been inoculated, but that is not happening everywhere.
Instead, two paths are emerging: In countries such as Israel, new COVID-19 cases are declining as vaccinations spread, while in other places such as the Seychelles — which has fully inoculated more of its population than any other nation — infections continue to increase or even reach new highs.
One reason for that might be the different types of vaccine being used. Evidence derived from the expanding global inoculation rollout indicates that the messenger RNA (mRNA) shots developed by Moderna or Pfizer and BioNTech are better at stopping people from becoming contagious.
Illustration: Yusha
This helps reduce onward transmission — an unexpected benefit as the first wave of COVID-19 vaccines were mostly intended to prevent people from becoming extremely ill.
Other vaccines, while effective in preventing acute illness or death from COVID-19, appear not to have this extra perk to the same degree.
“This will be an increasing trend as countries start to realize that some vaccines are better than others,” said Nikolai Petrovsky, a professor at the College of Medicine and Public Health at Flinders University in South Australia.
While the use of any vaccine “is still better than nothing,” some doses “may have little benefit in preventing spread, even if they reduce the risk of death or severe disease,” he said.
Studies of millions of people in Israel who were vaccinated with the Pfizer-BioNTech shot show the mRNA doses prevented more than 90 percent of asymptomatic infections — those who contract the virus but show no symptoms.
That is important, said Raina MacIntyre, an epidemiologist at the University of New South Wales in Sydney, because a vaccine’s ability to stop asymptomatic infection “is the determinant of whether or not herd immunity is possible.”
Herd immunity is typically achieved when the virus can no longer find any vulnerable hosts in order to keep spreading.
Which vaccines a country can secure could therefore affect everything from policy about mask wearing and social distancing to lifting border restrictions and reviving economies, given the influence that daily case counts have on government decisions.
For individuals, it might determine how soon they regain pre-pandemic freedoms.
The differences in effectiveness are already leading to preferred brands in countries where more than one vaccine is available. In the Philippines, immunization centers have been instructed not to announce which shots are being given after a crowd turned up at one location hoping to get access to the Pfizer shot.
In the US, nearly 40 percent of the population has been fully vaccinated, mostly with mRNA shots, and the number of new cases each day has dropped by more than 85 percent in the past four months. The CDC this month said those who are fully vaccinated can gather without masks or social distancing.
“If you are fully vaccinated, you can start doing things you have stopped doing because of the pandemic,” CDC Director Rochelle Walensky said. “We have all longed for this moment, when we can get back to some sense of normalcy.”
A similar trajectory is evident in Israel, which fully vaccinated nearly 60 percent of its population with the Pfizer-BioNTech shot and has gradually lifted restrictions as new cases declined to fewer than 50 a day, from more than 8,000 at the beginning of this year.
Qatar and Malta are also witnessing a decline in new cases after giving about 30 percent of their populations two doses of mostly mRNA vaccines.
LIMITED ACCESS
The results provide further evidence of the surprise efficacy of the new mRNA shots, given that the COVID-19 pandemic is the first time this vaccine technology has been widely used. They work by utilizing genetic codes that instruct the human body to make virus proteins that stimulate an immune response.
The existing mRNA shots require extremely cold storage, limiting their accessibility to countries with poor transport and storage infrastructure.
That is one reason why most countries are relying predominantly on non-mRNA shots, ranging from AstraZeneca’s adenovirus vector vaccine to those from Chinese developers Sinopharm and Sinovac Biotech, which use an inactivated form of the virus.
These traditional vaccine types have shown efficacy rates of between 50 to 80 percent in preventing symptomatic COVID-19 in clinical trials, compared with more than 90 percent for mRNA ones. There is little data regarding their ability to prevent onward transmission, but signs are emerging that it might be much lower.
“Real-world evidence is difficult to compare, as it is captured at different times, in different populations, in different places that might have different levels of COVID-19 infection and with different variants of the virus in circulation,” an AstraZeneca statement said.
Two doses of the AstraZeneca vaccine are about 85 to 90 percent effective against symptomatic disease, Public Health England last week said.
This is higher than the 66.7 percent efficacy rate found in clinical trials, although statistics are not yet available on the vaccine’s ability to prevent asymptomatic infection within the general public, outside of trials.
Sinopharm did not immediately respond to queries for this story.
The Seychelles, an archipelago in the Indian Ocean, has fully vaccinated about 65 percent of its population with AstraZeneca and Sinopharm shots, yet weekly new infections increased rapidly this month, with 37 percent of those patients having already received their two doses.
The surge led authorities to close schools, cancel sporting events and ban household gatherings. Among fully inoculated people, about 60 percent received the vaccine from Sinopharm and the rest received AstraZeneca’s shot.
In Chile, the steady increase in vaccinations using mostly Sinovac’s shot did not prevent the number of new daily cases from almost doubling between March and last month, despite administering enough doses to cover 30 percent of the population. Authorities had to reintroduce a lockdown across the country in late March.
In the Seychelles and Chile, the types of vaccines available seems to be only one of many factors affecting the spread of the disease. Policy failures in places that reacted too slowly to impose restrictions, or lifted them prematurely, have been a major contributor, as has speed of diagnosis and access to medical facilities. Different transmission rates of virus variants have also played a part.
Seychellois President Wavel Ramkalawan said transmission increased in his country after the nation’s world-beating vaccine rollout caused people to become less guarded.
Sinovac chief executive officer Yin Weidong (尹衛東) attributed Chile’s increase in infections to the health authorities prioritizing elderly people in their initial vaccination efforts.
“It’s normal that the country sees a resurgence of infections as social activities increase among the younger people who are mainly not inoculated,” he said.
VARIANT THREAT
What seems clear is that all the approved doses reduce the incidence of people becoming severely ill or dying from the disease — the primary goal of a vaccine. That takes pressure off hospitals and medical resources. Most new COVID-19 patients in the Seychelles, for example, are only experiencing mild symptoms, Ramkalawan said.
This is a crucial first step for countries without access to mRNA vaccines, University of Auckland vaccinologist Helen Petousis-Harris said. After using available vaccines to crush the number of severe cases, countries can stamp out remaining infections with shots that curb transmission once they become available.
Another possibility is that vaccination along with the spread of mild cases could also end up building herd immunity, said Ben Cowling, head of the University of Hong Kong’s department of epidemiology and biological statistics.
“The places with less immunity against infection, but more immunity against severe disease, will see circulation of the virus causing mainly mild infections, boosting immunity to a higher level,” Cowling said.
Experts say much remains unknown, and so-called breakthrough infections — where people who received shots still get COVID-19 — do occur, even with mRNA vaccines. It is also not yet fully known how well the different kinds of shots perform against the different variants of the virus.
A study conducted in Qatar among 260,000 people who completed two doses of Pfizer-BioNTech’s vaccine showed the mRNA shot’s effectiveness against the South African variant dipping to 75 percent.
The improvements in the US and Israel came before those places were affected by concerning new strains, which include variants that have emerged in Brazil and India.
“I would be careful about over-interpreting the data,” said Petrovsky, who points out that no studies have been performed to directly identify the best vaccines.
For the mRNA shots, “data on their effects on transmission is very limited,” he said.
The development of new, modified versions of the vaccines will be required to win the war against COVID-19, Petousis-Harris said. Some vaccine developers are working on nasal spray inoculations, which can prevent the virus from taking hold in the respiratory track, thus cutting off infection at its entry point.
“We’ve got some super vaccines that are beyond expectation,” she said. “We’ve learned a lot, so imagine what the next one is going to look like.”
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